UST CORP
S-4, 1996-11-05
STATE COMMERCIAL BANKS
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<PAGE>   1
 
    AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON NOVEMBER 5, 1996
                                                     REGISTRATION NO.
- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------
 
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                            ------------------------
 
                                    FORM S-4
            REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933
 
                                   UST CORP.
             (Exact name of registrant as specified in its charter)
 
                            ------------------------
 
<TABLE>
<S>                                            <C>
                MASSACHUSETTS                                   04-2436093
       (State or other jurisdiction of                       (I.R.S. Employer
       incorporation or organization)                       Identification No.)
</TABLE>
 
                                      6712
            (Primary Standard Industrial Classification Code Number)
 
                            ------------------------
 
          40 COURT STREET, BOSTON, MASSACHUSETTS 02108, (617) 726-7000
  (Address, including ZIP code, and telephone number, including area code, of
                   registrant's principal executive offices)
 
                            ------------------------
 
<TABLE>
<S>                                            <C>
                JAMES K. HUNT                              ERIC R. FISCHER, ESQ.
          Executive Vice President,                      Executive Vice President,
    Chief Financial Officer and Treasurer                General Counsel and Clerk
                  UST CORP.                                      UST CORP.
               40 Court Street                                40 Court Street
         Boston, Massachusetts 02108                    Boston, Massachusetts 02108
               (617) 726-7055                                 (617) 726-7377
</TABLE>
 
 (Names, addresses, including ZIP codes, and telephone numbers, including area
                         codes, of agents for service)
 
     Approximate date of commencement of proposed sale of the securities to the
public: As soon as practicable after the effective date of this Registration
Statement and all other conditions to the merger of a subsidiary of the
Registrant with and into Walden Bancorp, Inc. have been satisfied or waived as
described in the enclosed Joint Proxy Statement -- Prospectus.
 
                            ------------------------
 
     If the securities being registered on this Form are to be offered in
connection with the formation of a holding company and there is compliance with
General Instruction G, check the following box [ ].
 
                            ------------------------
 
                        CALCULATION OF REGISTRATION FEE
- --------------------------------------------------------------------------------
 
<TABLE>
<S>                          <C>              <C>              <C>              <C>
- --------------------------------------------------------------------------------
                                                               PROPOSED MAXIMUM
TITLE OF EACH CLASS               AMOUNT      PROPOSED MAXIMUM     AGGREGATE        AMOUNT OF
OF SECURITIES TO BE                TO BE       OFFERING PRICE      OFFERING       REGISTRATION
REGISTERED                     REGISTERED(1)    PER SHARE(2)       PRICE(3)          FEE(4)
- -------------------------------------------------------------------------------------------------
Common Stock, par value
  $0.625 per share(5)........    10,611,549          --         $181,010,692.66    $54,851.73
</TABLE>
 
- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------
 
(1) This Registration Statement covers the proposed maximum number of the
    Registrant's securities to be issued in the transaction described herein.
(2) Not applicable.
(3) Computed pursuant to Rule 457(f)(1), based upon the market value of the
    securities to be canceled in the merger, consisting of approximately
    5,585,026 shares of Walden common stock (including shares issuable upon the
    exercise of options to acquire Walden Common Stock).
(4) In accordance with Rule 457(b), the registration fee required to be paid
    herewith has been reduced by $35,857.25, which is the amount of the fee
    previously paid in connection with the Registrant's preliminary proxy
    statement filed with the Commission on Schedule 14A on October 15, 1996.
(5) Includes preferred stock purchase rights. Prior to the occurrence of certain
    events, the Rights will not be exercisable or evidenced separately from the
    Common Stock.
 
     THE REGISTRANT HEREBY AMENDS THIS REGISTRATION STATEMENT ON SUCH DATE OR
DATES AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANT SHALL
FILE A FURTHER AMENDMENT WHICH SPECIFICALLY STATES THAT THIS REGISTRATION
STATEMENT SHALL THEREAFTER BECOME EFFECTIVE IN ACCORDANCE WITH SECTION 8(A) OF
THE SECURITIES ACT OF 1933 OR UNTIL THE REGISTRATION STATEMENT SHALL BECOME
EFFECTIVE ON SUCH DATE AS THE COMMISSION, ACTING PURSUANT TO SAID SECTION 8(A),
MAY DETERMINE.
- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------
<PAGE>   2
 
                                   [UST LOGO]
 
                                                                November 5, 1996
 
To the Common Stockholders of UST CORP.:
 
     We are pleased to invite you to attend a Special Meeting of Stockholders
(the "UST Meeting") of UST Corp. ("UST"), which will be held on Tuesday,
December 17, 1996, at 10:00 a.m. in the Auditorium located on the 12th Floor of
UST's principal offices at 40 Court Street, Boston, Massachusetts 02108.
 
     At the UST Meeting, you will be asked to consider and vote upon a proposal
to approve and adopt an Affiliation Agreement and Plan of Reorganization (the
"Affiliation Agreement"), dated as of August 30, 1996, between UST and Walden
Bancorp, Inc. ("Walden"), and the corresponding Agreement and Plan of Merger,
dated as of August 30, 1996, among UST, its wholly-owned subsidiary, Mosaic
Corp. (the "Merger Subsidiary"), and Walden (the "Plan of Merger"), as well as
the transactions contemplated thereby, including specifically the issuance of
UST common stock to persons who were stockholders of Walden immediately prior to
the merger, pursuant to which the Merger Subsidiary will be merged (the
"Affiliation") with and into Walden. As a result of the Affiliation, Walden will
become a wholly-owned subsidiary of UST. As described in the accompanying Joint
Proxy Statement -- Prospectus, from and after the effective time of the
Affiliation, the Board of Directors of UST (the "UST Board") will be expanded by
three members and David E. Bradbury, the Chairman of the Board, President and
Chief Executive Officer of Walden, and two persons chosen by Walden and approved
of by UST prior to the effective time of the Affiliation, will be elected as
directors of UST by the UST Board. A copy of each of the Affiliation Agreement
and the Plan of Merger is attached to the accompanying Joint Proxy Statement -
Prospectus as Appendix A and Appendix B, respectively.
 
     At the effective time of the Affiliation, each share of Walden common
stock, par value $1.00 per share ("Walden Common Stock"), will be entitled to
receive 1.9 shares of UST common stock, par value $0.625 per share ("UST Common
Stock"). Fox-Pitt, Kelton Inc., UST's financial advisor, has advised the UST
Board, that in its opinion the conversion number of 1.9 is fair, from a
financial point of view, to UST.
 
     Enclosed are a Notice of Special Meeting of Stockholders and a Joint Proxy
Statement - Prospectus which describes the Affiliation and the background
thereof. You are urged to read all of these materials carefully. The UST Board
has fixed the close of business on November 4, 1996 as the record date for the
UST Meeting. Accordingly, only common stockholders of record on that date will
be entitled to notice of, and to vote at, the UST Meeting. The affirmative vote
of the holders of a majority of the shares of UST Common Stock present in
person, or represented by proxy, and entitled to vote and voting is necessary to
approve and adopt the Affiliation Agreement, the Plan of Merger and the
transactions contemplated thereby.
 
     THE BOARD OF DIRECTORS OF UST HAS UNANIMOUSLY APPROVED THE AFFILIATION
AGREEMENT, PLAN OF MERGER AND THE TRANSACTIONS CONTEMPLATED THEREBY, INCLUDING
THE AFFILIATION, AND UNANIMOUSLY RECOMMENDS THAT STOCKHOLDERS VOTE IN FAVOR OF
APPROVING AND ADOPTING THE AFFILIATION AGREEMENT, THE PLAN OF MERGER AND THE
CONSUMMATION OF THE TRANSACTIONS CONTEMPLATED THEREBY, INCLUDING THE
AFFILIATION.
 
     At the UST Meeting, you will also be asked to consider and vote upon
proposals to amend UST's Restated Articles of Organization (the "UST Articles")
to increase the number of authorized shares of UST Common Stock from 30,000,000
to 45,000,000.
 
     The UST Board recommends that stockholders vote FOR the proposed amendments
to the UST Articles. Stockholder approval of the amendment to the UST Articles
to increase the number of authorized shares requires the affirmative vote of the
holders of at least a majority of the outstanding shares of UST Common Stock.
<PAGE>   3
 
     If you plan to attend the meeting, please bring a form of personal
identification with you and, if you are acting as proxy for another, please
bring written confirmation from the record owner that you are acting as proxy.
Whether or not you expect to attend the meeting, please sign and date the
enclosed form of proxy and return it promptly in the accompanying envelope to
ensure that your shares will be represented. If you attend the meeting, you may
withdraw any proxy previously given and vote your shares in person.
 
     As President and Chief Executive Officer of UST my foremost responsibility
is to manage the company to maximize shareholder value. I strongly support the
Affiliation as an important contribution to that objective, and ask for your
support as well.
 
                                            Cordially,
 
                                            /s/ Neal F. Finnegan
 
                                            NEAL F. FINNEGAN
                                            President and Chief Executive
                                            Officer
 
                                        2
<PAGE>   4
 
                                   [UST LOGO]
 
                   NOTICE OF SPECIAL MEETING OF STOCKHOLDERS
                               DECEMBER 17, 1996
 
To the Common Stockholders of UST CORP.:
 
     NOTICE IS HEREBY GIVEN that a Special Meeting of Stockholders of UST Corp.
("UST") will be held in the Auditorium located on the 12th Floor of UST's
principal offices at 40 Court Street, Boston, Massachusetts 02108, on Tuesday,
December 17, 1996, at 10:00 a.m. (the "UST Meeting"), for the purpose of
considering and voting upon the following matters:
 
          1.  A proposal to approve and adopt the Affiliation Agreement and Plan
     of Reorganization, dated as of August 30, 1996 (the "Affiliation
     Agreement"), by and between UST Corp. ("UST") and Walden Bancorp, Inc.
     ("Walden"), including the Agreement and Plan of Merger, dated as of August
     30, 1996 (the "Plan of Merger"), by and among UST, Walden and Mosaic Corp.
     (the "Merger Subsidiary"), a wholly-owned subsidiary of UST organized under
     the laws of Massachusetts, and the transactions contemplated thereby,
     including the merger of Merger Subsidiary with and into Walden and the
     issuance of UST Common Stock to persons who were stockholders of Walden
     immediately prior to the merger, upon the terms and subject to the
     conditions set forth therein, as more fully described in the accompanying
     Joint Proxy Statement - Prospectus. A copy of each of the Affiliation
     Agreement and the Plan of Merger are attached as Appendix A and B,
     respectively, to the Joint Proxy Statement - Prospectus.
 
          2.  To authorize an amendment of UST's Restated Articles of
     Organization to increase the number of authorized shares of UST's common
     stock ("UST Common Stock") from 30,000,000 shares, par value $0.625 per
     share, to 45,000,000 shares, par value $0.625 per share.
 
          3.  Such other business as may properly be brought before the meeting
     or any adjournment or postponement thereof.
 
     Stockholder approval of the Affiliation Agreement, Plan of Merger and the
transactions contemplated thereby requires the affirmative vote of the holders
of at least a majority of the shares of UST Common Stock present, in person or
by proxy, entitled to vote, and voting at the UST Meeting. Stockholder approval
of the increase in the number of authorized shares requires the affirmative vote
of the holders of at least a majority of the outstanding shares of UST Common
Stock.
 
     In the event there are not sufficient votes to approve any one or more of
the foregoing proposals at the time of the UST Meeting, the meeting may be
adjourned by a majority of the votes present in order to permit further
solicitation of proxies.
 
     Only common stockholders of record at the close of business on November 4,
1996 are entitled to notice of, and to vote at, the UST Meeting and any and all
adjournments or postponements thereof.
<PAGE>   5
 
     It is important that your shares be represented at the UST Meeting
regardless of the number of shares you may hold. Please complete, sign and date
the enclosed form of proxy and return it promptly in the enclosed envelope which
requires no postage if mailed within the United States.
 
                                            By Order of the Board of Directors
 
                                            /s/ Eric R. Fischer
                                            ERIC R. FISCHER, Clerk
 
                                            Boston, Massachusetts
                                            November 5, 1996
 
                                        2
<PAGE>   6
 
                                     [LOGO]
 
                                                                November 5, 1996
 
To the Stockholders of Walden Bancorp, Inc.:
 
     We invite you to attend a Special Meeting of Stockholders of Walden
Bancorp, Inc. to be held at the Westford Regency Inn and Conference Center, 219
Littleton Road, Westford, Massachusetts, on Tuesday, December 17, 1996, at 11:00
a.m.
 
     At the special stockholder meeting, Walden stockholders will be asked to
approve an Affiliation Agreement and Plan of Reorganization between Walden and
UST Corp. pursuant to which Walden will become a wholly-owned subsidiary of UST
and each outstanding share of Walden Common Stock will be converted into 1.9
shares of UST Common Stock. Based on the last sale price of UST Common Stock on
November 4, 1996, the value of 1.9 shares of UST Common Stock as of that date
would have been approximately $33.61. The actual value of the UST Common Stock
to be received by Walden stockholders will depend on the market price of UST
Common Stock when the affiliation is consummated. Terms and conditions of the
affiliation are described in the accompanying Joint Proxy Statement -
Prospectus, which we urge you to read carefully.
 
     The consideration to be received by Walden stockholders in the affiliation
was negotiated under the direction of your Board of Directors in light of
various factors, including Walden's recent operating results, current financial
condition and future prospects. PaineWebber Incorporated, Walden's financial
advisor, has advised your Board of Directors that in its opinion the
consideration to be received by Walden stockholders in the affiliation is fair
to such stockholders from a financial point of view.
 
     YOUR BOARD OF DIRECTORS BELIEVES THAT THE PROPOSED AFFILIATION IS IN THE
BEST INTERESTS OF WALDEN STOCKHOLDERS. ACCORDINGLY, THE BOARD UNANIMOUSLY
RECOMMENDS THAT YOU VOTE TO APPROVE THE AFFILIATION.
 
     A proxy card is enclosed. Please sign, date and mail the proxy card
promptly in the return envelope provided. Because stockholder approval of the
affiliation requires the affirmative vote of the holders of at least two-thirds
of the outstanding shares of Walden Common Stock, it is important that you
return the proxy card, whether or not you plan to attend our special stockholder
meeting, so that your shares of Walden Common Stock can be voted.
 
                                            Sincerely,
 
                                            /s/ David E. Bradbury
 
                                            DAVID E. BRADBURY
                                            Chairman of the Board, President and
                                            Chief Executive Officer
<PAGE>   7
 
                                     [LOGO]
 
                   NOTICE OF SPECIAL MEETING OF STOCKHOLDERS
                               DECEMBER 17, 1996
 
     A Special Meeting of Stockholders of Walden Bancorp, Inc. ("Walden") will
be held at the Westford Regency Inn and Conference Center, 219 Littleton Road,
Westford, Massachusetts, on Tuesday, December 17, 1996, at 11:00 a.m.
 
     A Proxy Card and a Joint Proxy Statement - Prospectus are enclosed. The
purpose of our meeting is to consider and act upon:
 
          1.  A proposal to approve and adopt the Affiliation Agreement and Plan
     of Reorganization dated as of August 30, 1996 (the "Affiliation
     Agreement"), between Walden and UST Corp. ("UST"), including the Agreement
     and Plan of Merger among UST, a newly formed corporate subsidiary of UST,
     and Walden dated as of August 30, 1996 (the "Plan of Merger"), and the
     transactions contemplated thereby, pursuant to which the UST subsidiary
     will merge with and into Walden, and each outstanding share of Walden
     Common Stock will be converted into 1.9 shares of UST Common Stock, upon
     the terms and subject to the conditions set forth therein, as described in
     the accompanying Joint Proxy Statement - Prospectus. A copy of each of the
     Affiliation Agreement and Plan of Merger is attached as Appendix A and B,
     respectively, to the accompanying Joint Proxy Statement - Prospectus; and
 
          2.  Such other matters as may properly come before the meeting or any
     adjournments thereof.
 
     The Board of Directors is not aware of any other business to come before
the meeting.
 
     Stockholder approval of the Affiliation Agreement and the transactions
contemplated thereby requires the affirmative vote of the holders of at least
two-thirds of the outstanding shares of Walden Common Stock. In the event there
are not sufficient votes to approve the foregoing proposal at the time of the
meeting, the meeting may be adjourned by a majority of the votes present in
order to permit further solicitation of proxies by Walden.
 
     Any action may be taken on any matter properly brought before the meeting
on the date specified above, or on any date or dates less than 30 days later to
which, by original or later adjournment, the meeting may be adjourned.
Stockholders of record at the close of business on November 4, 1996 are the
stockholders entitled to vote at the meeting and any such adjournments thereto.
 
     You are requested to fill in and sign the enclosed Proxy Card that is
solicited by the Board of Directors and to mail it promptly in the enclosed
envelope. If you attend the meeting, you may revoke your proxy and vote at the
meeting in person.
                                            /s/ Josiah S. Cushing, II
 
                                            JOSIAH S. CUSHING, II
                                            Clerk
Acton, Massachusetts
November 5, 1996
 
                           NOTICE OF APPRAISAL RIGHTS
 
     If the Affiliation Agreement and Plan of Merger is approved by the
stockholders at the Walden Meeting and the Affiliation is consummated, any
stockholder (1) who files with Walden before the taking of the vote on the
approval of the Affiliation Agreement and Plan of Merger written objection to
the proposed Affiliation stating that he or she intends to demand payment for
his or her shares if the Affiliation is consummated and (2) whose shares are not
voted in favor of such action has or may have the right to demand in writing
from Walden (as it exists after the Affiliation), within twenty days after the
date of mailing to him or her of notice in writing that the Affiliation has been
consummated, payment for his or her shares and an appraisal of the value
thereof. Walden and any such stockholder shall in such cases have the rights and
duties and shall follow the procedure set forth in sections 85 to 98, inclusive,
of Chapter 156B of the General Laws of Massachusetts, copies of which are
attached as Appendix F to the accompanying Joint Proxy Statement - Prospectus.
See "THE AFFILIATION -- Rights of Dissenting Stockholders" in the Joint Proxy
Statement - Prospectus for more information.
<PAGE>   8
 
<TABLE>
<S>                             <C>
UST Corp.                       Walden Bancorp, Inc.
40 Court Street                 125 Nagog Park
Boston, Massachusetts 02108     Acton, Massachusetts 01720
</TABLE>
 
                       JOINT PROXY STATEMENT - PROSPECTUS
                            ------------------------
 
                                   [UST LOGO]
 
                        SPECIAL MEETING OF STOCKHOLDERS
                                   UST CORP.
 
                             [WALDEN BANCORP LOGO]
 
                        SPECIAL MEETING OF STOCKHOLDERS
                              WALDEN BANCORP, INC.
                            ------------------------
 
                               DECEMBER 17, 1996
 
     This Joint Proxy Statement - Prospectus is being furnished to stockholders
of UST Corp. ("UST") in connection with the solicitation of proxies by the Board
of Directors of UST (the "UST Board") to be used at the Special Meeting of
Stockholders of UST to be held on Tuesday, December 17, 1996, at 10:00 a.m. in
the Auditorium located on the 12th Floor of UST's principal offices at 40 Court
Street, Boston, Massachusetts 02108, and at any adjournments or postponements
thereof (the "UST Meeting"). At the UST Meeting, the holders of the common stock
of UST, par value $0.625 per share (the "UST Common Stock"), will consider and
vote upon a proposal to approve and adopt an Affiliation Agreement and Plan of
Reorganization dated as of August 30, 1996 (the "Affiliation Agreement") by and
between UST and Walden Bancorp, Inc. ("Walden"), and the related Agreement and
Plan of Merger, dated as of August 30, 1996 (the "Plan of Merger"), by and among
UST, Walden and Mosaic Corp. (the "Merger Subsidiary"), a Massachusetts
corporation and wholly-owned subsidiary of UST, and the transactions
contemplated thereby, pursuant to which the Merger Subsidiary will be merged
with and into Walden, with Walden being the surviving corporation and becoming a
wholly-owned subsidiary of UST (the "Affiliation"). See "THE UST MEETING --
Date, Time and Place" and " -- Purposes of the Meeting."
 
     This Joint Proxy Statement - Prospectus is being furnished to stockholders
of Walden in connection with the solicitation of proxies by the Board of
Directors of Walden (the "Walden Board") to be used at the Special Meeting to be
held on Tuesday, December 17, 1996, at 11:00 a.m., at the Westford Regency Inn
and Conference Center, 219 Littleton Road, Westford, Massachusetts, and at any
adjournments or postponements thereof (the "Walden Meeting"). At the Walden
Meeting, the holders of the common stock, par value $1.00 per share (the "Walden
Common Stock"), will consider and vote upon a proposal to approve and adopt the
Affiliation Agreement and the Plan of Merger and the transactions contemplated
thereby. See "THE WALDEN MEETING -- Date, Time and Place" and " -- Purposes of
the Meeting."
 
     The Affiliation Agreement and the Plan of Merger are attached hereto as
APPENDIX A and B, respectively, and are incorporated herein by reference.
 
     This Joint Proxy Statement - Prospectus is also being furnished to holders
of UST Common Stock to approve a proposal to amend UST's Restated Articles of
Organization (the "UST Articles") to increase the number of authorized shares of
UST Common Stock from 30,000,000 to 45,000,000. Information with respect to this
proposal and additional matters to be considered at the UST Meeting is being
furnished separately to
<PAGE>   9
 
the stockholders of UST in this Joint Proxy Statement - Prospectus. See "THE UST
MEETING -- Purposes of the Meeting," and "THE UST MEETING -- ADDITIONAL
MATTERS."
 
     Upon consummation of the Affiliation, each share of Walden Common Stock
issued and outstanding immediately prior to the effective time of the
Affiliation (other than certain shares held in Walden's treasury or held by UST,
except in a fiduciary capacity, or Walden or any subsidiary thereof and shares
held by dissenting stockholders who have duly perfected their rights of
appraisal (the "Dissenting Shares")), will be converted into 1.9 shares of UST
Common Stock. See "THE AFFILIATION -- Conversion of Shares." The transaction is
subject to various conditions, including approval by the respective stockholders
of UST and Walden, and approval by applicable regulatory authorities. See "THE
AFFILIATION -- Regulatory Approvals Required for the Affiliation" and " --
Conditions to the Consummation of the Affiliation."
 
     UST Common Stock is quoted on, and transactions in UST Common Stock are
effected through, the National Association of Securities Dealers Automated
Quotation system ("NASDAQ") National Market. The last reported sale price of UST
Common Stock on November 4, 1996, was $17.6875.
 
     This Joint Proxy Statement - Prospectus does not cover any resales of UST
Common Stock received by stockholders of Walden upon consummation of the
Affiliation, and no person is authorized to make use of this Joint Proxy
Statement - Prospectus in connection with any such resale. See "THE AFFILIATION
- -- Resales of UST Common Stock."
 
     All information concerning UST contained in this Joint Proxy Statement -
Prospectus has been furnished by UST, and all information concerning Walden has
been furnished by Walden. UST has represented and warranted to Walden, and
Walden has represented and warranted to UST, that the particular information so
furnished does not contain any untrue statement of a material fact or omit to
state a material fact necessary to make such information not misleading. See
"EXPERTS" with respect to the financial statements of UST and Walden. For a more
complete description of the terms of the Affiliation and the Affiliation
Agreement, see generally "THE AFFILIATION."
 
     UST has filed a Registration Statement on Form S-4 (together with its
exhibits, the "Registration Statement") under the Securities Act of 1933, as
amended (the "Securities Act"), with the Securities and Exchange Commission (the
"Commission") covering a maximum of 10,611,549 shares of UST Common Stock,
representing shares to be issued in connection with the Affiliation. This Joint
Proxy Statement - Prospectus also constitutes the Prospectus of UST filed as a
part of such Registration Statement.
 
     This Joint Proxy Statement - Prospectus and the form of proxy are first
being mailed to stockholders of UST and Walden on or about November 12, 1996.
 
     The Above Matters Are Discussed In Detail In This Joint Proxy Statement -
Prospectus. The Proposed Affiliation Is A Complex Transaction. Stockholders Are
Strongly Urged To Carefully Read And Consider This Joint Proxy Statement -
Prospectus In Its Entirety.
                            ------------------------
 
     THE SHARES OF UST COMMON STOCK AND THE SHARES OF WALDEN COMMON STOCK ARE
NOT SAVINGS ACCOUNTS, DEPOSITS OR OTHER OBLIGATIONS OF ANY BANK OR NON-BANK
SUBSIDIARY OF UST OR WALDEN AND ARE NOT INSURED BY THE FEDERAL DEPOSIT INSURANCE
CORPORATION, THE BANK INSURANCE FUND OR ANY OTHER FEDERAL OR STATE GOVERNMENT
AGENCY.
 
     THE SECURITIES OFFERED HEREBY HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE
SECURITIES AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION NOR HAS
THE SECURITIES AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION PASSED
UPON THE ACCURACY OR ADEQUACY OF THIS JOINT PROXY STATEMENT - PROSPECTUS. ANY
REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.
                            ------------------------
 
    THE DATE OF THIS JOINT PROXY STATEMENT - PROSPECTUS IS NOVEMBER 5, 1996.
 
                                        2
<PAGE>   10
 
                               TABLE OF CONTENTS
 
<TABLE>
<CAPTION>
                                                                                        PAGE
                                                                                        ----
<S>                                                                                     <C>
AVAILABLE INFORMATION.................................................................    1
CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS.............................    1
INCORPORATION OF CERTAIN INFORMATION BY REFERENCE.....................................    2
SUMMARY
     The Companies....................................................................    3
          UST.........................................................................    3
          Walden......................................................................    3
     The Affiliation..................................................................    3
     Certain Terms of the Option Agreement............................................    4
     Date, Time and Place of the UST Meeting and the Walden Meeting...................    4
     Purposes of the UST Meeting and the Walden Meeting...............................    5
          UST.........................................................................    5
          Walden......................................................................    5
     Vote Required at the UST Meeting and the Walden Meeting..........................    5
          UST.........................................................................    5
          Walden......................................................................    5
     Recommendations of the Boards and Reason for the Affiliation.....................    6
     Opinions of Financial Advisors...................................................    6
     Regulatory Approvals Required for the Affiliation................................    6
     Certain Federal Income Tax Consequences..........................................    7
     Accounting Treatment.............................................................    7
     Employee Matters.................................................................    7
     Interests of Certain Persons in the Affiliation; Indemnification and Insurance...    8
     Rights of Dissenting Stockholders................................................    8
     Comparative Rights of Stockholders...............................................    8
     Conditions to Consummation of the Affiliation....................................    8
     Conduct of Business Pending the Affiliation......................................    9
     Waiver and Amendment.............................................................    9
     Management and Operations after the Affiliation..................................    9
     Termination of the Affiliation Agreement.........................................   10
     Market and Market Prices.........................................................   10
     UST Corp. and Subsidiaries Selected Financial Data...............................   11
     Walden Bancorp, Inc. and Subsidiaries Selected Financial Data....................   12
     UST Corp. and Subsidiaries and Walden Bancorp, Inc. and Subsidiaries Pro Forma
      Combined Selected Financial Data................................................   13
     UST Capitalization...............................................................   14
     Comparative Per Share Data (Unaudited)...........................................   15
THE UST MEETING
     Date, Time and Place.............................................................   16
     Purposes of Meeting..............................................................   16
     Record Date......................................................................   16
     Proxies; Voting and Revocation...................................................   16
     Votes Required to Approve the Affiliation and Other Matters; Abstentions and
      Non-votes.......................................................................   17
     Ownership of UST Common Stock by UST Officers and Directors......................   17
THE WALDEN MEETING
     Date, Time and Place.............................................................   18
     Purposes of Meeting..............................................................   18
     Record Date......................................................................   18
     Proxies; Voting and Revocation...................................................   18
     Votes Required to Approve the Affiliation and Other Matters; Abstentions and
      Non-votes.......................................................................   18
     Ownership of Walden Common Stock by Walden Officers and Directors................   19
INFORMATION ABOUT UST.................................................................   19
     Recent Developments..............................................................   20
INFORMATION ABOUT WALDEN..............................................................   21
     Recent Developments..............................................................   21
</TABLE>
 
                                        i
<PAGE>   11
 
<TABLE>
<CAPTION>
                                                                                        PAGE
                                                                                        ----
<S>                                                                                     <C>
THE AFFILIATION
     General..........................................................................   22
     Background of the Affiliation....................................................   22
     Recommendation of the UST Board; Reasons for the Affiliation.....................   25
     Recommendation of the Walden Board; Reasons for the Affiliation..................   25
     Opinion of Financial Advisor to UST..............................................   26
     Opinion of Financial Advisor to Walden...........................................   29
     Effective Time of the Affiliation; Closing Date..................................   34
     Terms of the Affiliation.........................................................   34
     Regulatory Approvals Required for the Affiliation................................   35
          Federal Reserve.............................................................   35
          Massachusetts Approval......................................................   36
     Certain Federal Income Tax Consequences..........................................   37
          General.....................................................................   37
          Effect of the Affiliation...................................................   37
          Backup Withholding..........................................................   38
     Accounting Treatment.............................................................   38
     Employee Matters.................................................................   39
     Interests of Certain Persons in the Affiliation..................................   39
     Indemnification and Insurance....................................................   40
     Rights of Dissenting Stockholders................................................   40
     NASDAQ Listing...................................................................   41
     Resales by Affiliates............................................................   41
     Conversion of Shares; Exchange of Certificates...................................   42
     Conditions to the Consummation of the Affiliation................................   44
     Conduct of Business Pending the Affiliation......................................   46
     Waiver and Amendment.............................................................   49
     Expenses.........................................................................   49
     Management and Operations after the Affiliation..................................   49
          UST.........................................................................   49
          Walden......................................................................   49
          Walden Subsidiaries.........................................................   50
     Termination of the Affiliation Agreement.........................................   50
CERTAIN TERMS OF THE STOCK OPTION AGREEMENT
     General..........................................................................   51
     Grant of Option..................................................................   51
     Triggering Events; Exercise of Option............................................   51
     Repurchase of Option.............................................................   52
     Conversion of Option.............................................................   53
     Registration Rights..............................................................   53
     Assignment of Option.............................................................   53
     Additional Provisions............................................................   54
UNAUDITED PRO FORMA CONDENSED FINANCIAL INFORMATION
     Unaudited Pro Forma Condensed Combining Balance Sheet............................   55
     Unaudited Pro Forma Condensed Combining Statements of Income.....................   57
     Notes to Unaudited Pro Forma Condensed Financial Information.....................   63
CERTAIN REGULATORY CONSIDERATIONS.....................................................   68
     General..........................................................................   68
     Dividends........................................................................   68
     Legislation and Related Matters..................................................   69
     Other Proposals..................................................................   72
DESCRIPTION OF UST CAPITAL STOCK
     General..........................................................................   73
     Common Stock.....................................................................   73
          Dividend Rights.............................................................   73
          Voting Rights...............................................................   73
          Preemptive Rights...........................................................   73
          Liquidation Rights..........................................................   73
</TABLE>
 
                                       ii
<PAGE>   12
 
                           [ALTERNATE UST PAGE ONLY]
 
<TABLE>
<S>                                                                                     <C>
          Assessments.................................................................   73
          Transfer Agent and Registrar................................................   73
          Stockholder Rights Agreement................................................   73
     Preferred Stock..................................................................   74
          General.....................................................................   74
          Dividend and Liquidation Rights.............................................   74
          Determinations to be Made by the UST Board..................................   74
          Series A Junior Participating Preferred Stock...............................   75
COMPARATIVE RIGHTS OF STOCKHOLDERS
     General..........................................................................   76
     Size and Classification of the Board of Directors................................   76
     Removal of Directors.............................................................   76
     Stockholder Nominations..........................................................   76
          UST.........................................................................   76
          Walden......................................................................   76
     Interested Transactions..........................................................   76
          UST.........................................................................   76
          Walden......................................................................   76
     Meetings of Stockholders.........................................................   77
          UST.........................................................................   77
          Walden......................................................................   77
     Stockholder Action Without A Meeting.............................................   77
          UST.........................................................................   77
          Walden......................................................................   77
     Amendment of By-laws.............................................................   77
          UST.........................................................................   77
          Walden......................................................................   77
     Required Vote for Certain Business Combinations..................................   77
          UST.........................................................................   77
          Walden......................................................................   78
     Stockholder Rights Plan..........................................................   78
          UST.........................................................................   78
          Walden......................................................................   78
     State Anti-takeover Statutes.....................................................   79
MARKET PRICES AND DIVIDENDS...........................................................   79
EXPERTS...............................................................................   79
LEGAL OPINIONS........................................................................   80
MANAGEMENT AND ADDITIONAL INFORMATION.................................................   80
SOLICITATION OF PROXIES...............................................................   80
THE UST MEETING -- ADDITIONAL MATTERS.................................................   82
     Increase In Number of Authorized Shares of UST Common Stock......................   82
STOCKHOLDER PROPOSALS.................................................................   83
APPENDIX A -- AFFILIATION AGREEMENT AND PLAN OF REORGANIZATION
APPENDIX B -- AGREEMENT AND PLAN OF MERGER
APPENDIX C -- STOCK OPTION AGREEMENT
APPENDIX D -- OPINION OF FINANCIAL ADVISOR TO UST
APPENDIX E -- OPINION OF FINANCIAL ADVISOR TO WALDEN
APPENDIX F -- INTENTIONALLY OMITTED. THIS APPENDIX APPLIES ONLY TO DISSENTING
  STOCKHOLDERS, IF ANY, OF WALDEN.
</TABLE>
 
                                       iii
<PAGE>   13
 
                          [ALTERNATE WALDEN PAGE ONLY]
 
<TABLE>
<S>                                                                                     <C>
          Assessments.................................................................   73
          Transfer Agent and Registrar................................................   73
          Stockholder Rights Agreement................................................   73
     Preferred Stock..................................................................   74
          General.....................................................................   74
          Dividend and Liquidation Rights.............................................   74
          Determinations to be Made by the UST Board..................................   74
          Series A Junior Participating Preferred Stock...............................   75
COMPARATIVE RIGHTS OF STOCKHOLDERS
     General..........................................................................   76
     Size and Classification of the Board of Directors................................   76
     Removal of Directors.............................................................   76
     Stockholder Nominations..........................................................   76
          UST.........................................................................   76
          Walden......................................................................   76
     Interested Transactions..........................................................   76
          UST.........................................................................   76
          Walden......................................................................   76
     Meetings of Stockholders.........................................................   77
          UST.........................................................................   77
          Walden......................................................................   77
     Stockholder Action Without A Meeting.............................................   77
          UST.........................................................................   77
          Walden......................................................................   77
     Amendment of By-laws.............................................................   77
          UST.........................................................................   77
          Walden......................................................................   77
     Required Vote for Certain Business Combinations..................................   77
          UST.........................................................................   77
          Walden......................................................................   78
     Stockholder Rights Plan..........................................................   78
          UST.........................................................................   78
          Walden......................................................................   78
     State Anti-takeover Statutes.....................................................   79
MARKET PRICES AND DIVIDENDS...........................................................   79
EXPERTS...............................................................................   79
LEGAL OPINIONS........................................................................   80
MANAGEMENT AND ADDITIONAL INFORMATION.................................................   80
SOLICITATION OF PROXIES...............................................................   80
STOCKHOLDER PROPOSALS.................................................................   81
APPENDIX A -- AFFILIATION AGREEMENT AND PLAN OF REORGANIZATION
APPENDIX B -- AGREEMENT AND PLAN OF MERGER
APPENDIX C -- STOCK OPTION AGREEMENT
APPENDIX D -- OPINION OF FINANCIAL ADVISOR TO UST
APPENDIX E -- OPINION OF FINANCIAL ADVISOR TO WALDEN
APPENDIX F -- TEXT OF SECTIONS 85 TO 98 OF THE MASSACHUSETTS BUSINESS CORPORATION LAW
</TABLE>
 
                                       iii
<PAGE>   14
 
                             AVAILABLE INFORMATION
 
     UST and Walden are subject to the informational requirements of the
Securities Exchange Act of 1934, as amended (the "Exchange Act"), and in
accordance therewith file reports, proxy statements and other information with
the Securities and Exchange Commission (the "Commission"). Such reports, proxy
statements and other information filed by UST and Walden can be inspected and
copied at the public reference facilities maintained by the Commission at 450
Fifth Street, Room 1024 N.W., Washington, D.C. 20549 and at the Commission's
regional offices at Northwestern Atrium Center, 500 West Madison Street, Suite
1400, Chicago, Illinois 60661, and 7 World Trade Center, Suite 1300, New York,
New York 10048. Copies of such material can be obtained from the Public
Reference Section of the Commission, 450 Fifth Street, Room 1024, N.W.,
Washington, D.C. 20549 at prescribed rates.
 
     This Joint Proxy Statement -- Prospectus does not contain all of the
information set forth in the Registration Statement on Form S-4 (the
"Registration Statement") (and exhibits thereto) which UST has filed with the
Commission under the Securities Act of 1933, as amended (the "Securities Act"),
and to which reference is hereby made. The Registration Statement (and exhibits
thereto) may be inspected at the public reference facilities of the Commission
at 450 Fifth Street, Room 1024, N.W., Washington, D.C. 20549, and copies thereof
may be obtained from the Commission at prescribed rates.
 
     The Commission also maintains an internet site (http://www.sec.gov) that
contains information regarding UST and Walden's electronic filings with the
Commission. Before December 1995, The Co-operative Bank of Concord ("Concord")
and The Braintree Savings Bank (known as The Bank of Braintree and herein
referred to as such or "Braintree") were subject to the informational
requirements of the Exchange Act and, in accordance therewith, filed reports,
proxy statements and other information with the Federal Deposit Insurance
Corporation ("FDIC"). Such information can be inspected at the public reference
facilities maintained by the FDIC at the Registration and Disclosure Section,
Federal Deposit Insurance Corporation, 1776 F Street, N.W., 6th Floor,
Washington, D.C. 20006 (telephone requests for such information or copies of
documents may be directed to (202) 898-8920).
 
           CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING INFORMATION
 
     This Proxy Statement -- Prospectus contains or reflects certain
forward-looking information, including without limitation certain statements
under "THE AFFILIATION -- Opinion of Financial Advisor to UST," "-- Opinion of
Financial Advisor to Walden," "UNAUDITED PRO FORMA CONDENSED FINANCIAL
INFORMATION" and "NOTES TO UNAUDITED PRO FORMA CONDENSED FINANCIAL INFORMATION"
regarding future performance and "INFORMATION ABOUT UST -- Recent Developments"
and "CERTAIN REGULATORY CONSIDERATIONS -- Dividends" regarding the possible
effect of capital requirements on the payment of dividends by UST in connection
with regulatory approval of the acquisition by UST's lead banking subsidiary,
USTrust, of twenty branches from The First National Bank of Boston. Moreover,
UST and/or Walden may from time to time, in both written reports and oral
statements by UST and Walden's senior management, express its expectations
regarding future performance of UST and Walden. All forward-looking information
is inherently uncertain, and shareholders of UST and Walden must recognize that
actual results may differ materially from the assumptions, estimates or
expectations reflected or contained in the forward-looking information. Future
performance of UST and Walden and their respective subsidiaries is influenced by
a number of factors substantially beyond the control of UST and/or Walden,
including, but not limited to: (i) changes in asset quality and resulting credit
risk-related expenses, (ii) general foreign and domestic economic conditions,
and adverse changes in the economy and/or the real estate market of the New
England region, (iii) the monetary and fiscal policies of the United States
government and federal agencies, (iv) fluctuations in market rates and pricing,
(v) changes in federal and state regulatory requirements and (vi) increased
competition in the Massachusetts and Northeast banking markets.
<PAGE>   15
 
               INCORPORATION OF CERTAIN INFORMATION BY REFERENCE
 
     There are hereby incorporated by reference in this Joint Proxy Statement -
Prospectus the following documents and information heretofore filed with the
Commission, which documents are not presented herein or delivered herewith:
 
     UST's:
 
        1.  Annual Report on Form 10-K filed for its fiscal year ended December
            31, 1995;
 
        2.  Quarterly Reports on Form 10-Q filed since December 31, 1995;
 
        3.  Current Reports on Form 8-K filed since December 31, 1995; and
 
        4.  Description of its Common Stock contained in its registration
            statement filed under Section 12 of the Exchange Act, including any
            amendment or report filed for the purpose of updating such
            description.
 
     Walden's:
 
        1.  Annual Report on Form 10-K for the fiscal year ended December 31,
            1995;
 
        2.  Quarterly Reports on Form 10-Q filed since December 31, 1995; and
 
        3.  Current Reports on Form 8-K filed since December 31, 1995.
 
     All documents subsequently filed by UST or Walden pursuant to Sections
13(a), 13(c), 14 or 15(d) of the Exchange Act prior to the date of the UST
Meeting and the Walden Meeting shall be deemed to be incorporated by reference
into this Joint Proxy Statement - Prospectus and to be a part hereof from the
date of filing of such documents. Any statement contained in a document
incorporated or deemed to be incorporated by reference herein shall be deemed to
be modified or superseded for purposes of this Joint Proxy Statement -
Prospectus to the extent that a statement contained herein, or in any
subsequently filed document which also is or is deemed to be incorporated by
reference herein, modifies or supersedes such statement. Any statement so
modified or superseded shall not be deemed, except as so modified or superseded,
to constitute a part of this Joint Proxy Statement - Prospectus.
 
     UST AND WALDEN WILL PROVIDE UPON REQUEST AND WITHOUT CHARGE TO EACH PERSON
TO WHOM THIS PROXY STATEMENT - PROSPECTUS IS DELIVERED, A COPY OF ANY OR ALL OF
THE FOREGOING DOCUMENTS INCORPORATED HEREIN BY REFERENCE (OTHER THAN EXHIBITS TO
SUCH DOCUMENTS WHICH ARE NOT SPECIFICALLY INCORPORATED THEREIN BY REFERENCE).
WRITTEN REQUESTS FOR DOCUMENTS RELATING TO UST SHOULD BE DIRECTED TO ERIC R.
FISCHER, EXECUTIVE VICE PRESIDENT, GENERAL COUNSEL AND CLERK, UST CORP., 40
COURT STREET, BOSTON, MASSACHUSETTS 02108. TELEPHONE REQUESTS MAY BE DIRECTED TO
MR. FISCHER AT (617) 726-7377. WRITTEN REQUESTS FOR DOCUMENTS RELATING TO WALDEN
SHOULD BE DIRECTED TO LISA BERGEMANN, EXECUTIVE VICE PRESIDENT, WALDEN BANCORP,
INC., 125 NAGOG PARK, ACTON, MASSACHUSETTS 01720. TELEPHONE REQUESTS MAY BE
DIRECTED TO MS. BERGEMANN AT (508) 635-5000. IN ORDER TO ENSURE TIMELY DELIVERY
OF ANY OF THE DOCUMENTS, REQUESTS SHOULD BE MADE BY NOVEMBER 29, 1996.
 
     NO PERSON IS AUTHORIZED TO GIVE ANY INFORMATION OR TO MAKE ANY
REPRESENTATIONS NOT CONTAINED IN THIS JOINT PROXY STATEMENT - PROSPECTUS OR
INCORPORATED BY REFERENCE HEREIN, AND, IF GIVEN OR MADE, SUCH INFORMATION OR
REPRESENTATIONS MUST NOT BE RELIED UPON AS HAVING BEEN AUTHORIZED BY UST OR
WALDEN. THIS JOINT PROXY STATEMENT - PROSPECTUS DOES NOT CONSTITUTE AN OFFER TO
SELL OR A SOLICITATION OF AN OFFER TO PURCHASE THE UST COMMON STOCK OFFERED BY
THIS JOINT PROXY STATEMENT - PROSPECTUS, NOR DOES IT CONSTITUTE THE SOLICITATION
OF A PROXY, WITHIN ANY JURISDICTION TO OR FROM ANY PERSON TO OR FROM WHOM IT IS
UNLAWFUL TO MAKE SUCH OFFER OR SOLICITATION OF AN OFFER, OR PROXY SOLICITATION,
WITHIN SUCH JURISDICTION. NEITHER THE DELIVERY OF THIS JOINT PROXY STATEMENT -
PROSPECTUS NOR THE DISTRIBUTION OF SECURITIES HEREUNDER SHALL, UNDER ANY
CIRCUMSTANCES, CREATE AN IMPLICATION THAT THERE HAS BEEN NO CHANGE IN THE
AFFAIRS OF UST OR WALDEN SINCE THE DATE HEREOF OR THAT THE INFORMATION HEREIN OR
IN THE DOCUMENTS INCORPORATED HEREIN BY REFERENCE IS CORRECT AS OF ANY TIME
SUBSEQUENT TO THE DATE HEREOF OR THE DATES THEREOF.
 
                                        2
<PAGE>   16
 
                                    SUMMARY
 
     The following summary is not intended to be complete and is qualified in
its entirety by reference to more detailed information contained elsewhere in
this Joint Proxy Statement - Prospectus or incorporated by reference in this
Joint Proxy Statement - Prospectus, or in the accompanying Appendices and the
documents referred to herein. Capitalized terms which are used and not defined
in this Joint Proxy Statement - Prospectus have the meaning set forth in the
Affiliation Agreement.
 
THE COMPANIES
     UST.  UST is a registered bank holding company, organized as a
Massachusetts business corporation in 1967, that, through its subsidiaries is
engaged in providing financial services to individuals and small- and
medium-sized companies as well as trust and money management services to
individuals, corporations and other organizations. As of the close of business
on September 30, 1996, UST's total assets were approximately $2.03 billion and
USTrust, the lead banking subsidiary of UST had over $1.92 billion or 94% of
UST's consolidated assets. See "INFORMATION ABOUT UST." For a discussion of
UST's recent developments including the pending acquisition of a total of twenty
new branches and the pending sale of one of its bank subsidiaries, see
"INFORMATION ABOUT UST -- Recent Developments."
 
     The executive office of UST is located at 40 Court Street, Boston,
Massachusetts 02108 (Telephone (617) 726-7000).
 
     Walden.  Walden, a registered bank holding company, is a full service
commercial banking company with assets of $1 billion, headquartered in Acton,
Massachusetts. Walden and its banking subsidiaries, The Co-operative Bank of
Concord and The Bank of Braintree, provide financial products and services to
businesses and individuals through a network of 17 banking offices throughout
Eastern Massachusetts. See "INFORMATION ABOUT WALDEN."
 
     The executive office of Walden is located at 125 Nagog Park, Acton,
Massachusetts 01720 (Telephone (508) 635-5000).
 
THE AFFILIATION
 
     The Affiliation Agreement and the Plan of Merger provide for the merger of
Merger Subsidiary with and into Walden, with Walden as the surviving corporation
and a wholly-owned subsidiary of UST. Except in the limited circumstance
described under "THE AFFILIATION -- Terms of the Affiliation," upon the
consummation of the Affiliation, each outstanding share of Walden Common Stock
will be converted into 1.9 shares of UST Common Stock (the "Conversion Number"),
together with a corresponding number of preferred stock purchase rights issued
pursuant to the UST Rights Agreement, dated as of September 19, 1995 (the "UST
Rights Agreement"), provided that the following types of shares shall not be
converted (i) shares of Walden Common Stock which are held directly or
indirectly by UST unless held by UST in a fiduciary capacity, (ii) shares of
Walden Common Stock held as treasury shares by Walden, and (iii) Dissenting
Shares. Where a holder of Walden Common Stock has shares of record represented
by two or more certificates, the certificates will be aggregated.
 
     The Conversion Number is the product of arms' length negotiations between
the respective managements of Walden and UST. In negotiating the Conversion
Number, management of UST had the benefit of advice from its financial advisor,
the investment banking firm of Fox-Pitt, Kelton Inc. ("Fox-Pitt, Kelton") and
the management of Walden had the benefit of advice from its financial advisor,
the investment banking firm of PaineWebber Incorporated ("PaineWebber"). See
"THE AFFILIATION -- Opinion of Financial Advisor to UST" and "-- Opinion of
Financial Advisor to Walden."
 
     As set forth in the Affiliation Agreement, if the average per share last
reported sale prices of UST Common Stock as reported on National Association of
Securities Dealers Automated Quotation System ("NASDAQ") National Market over
the 10 consecutive trading days immediately preceding the date of the receipt of
the last Requisite Regulatory Approval (as defined below) (the "Closing Price")
is less than $13.81 and the price of UST Common Stock has declined more than 15%
relative to a certain bank stock index, the
 
                                        3
<PAGE>   17
 
Walden Board may give written notice of its intention to terminate the
Affiliation Agreement. However, in the event that Walden notifies UST of its
intention to exercise its termination right pursuant to the foregoing sentence,
UST may choose, as provided in the Affiliation Agreement, to increase the
consideration to be paid to Walden stockholders by increasing the Conversion
Number pursuant to the formula set forth in the Affiliation Agreement, in which
case the Affiliation Agreement will remain in full force and effect. See "THE
AFFILIATION -- Termination of the Affiliation Agreement."
 
     No fractional shares of UST Common Stock will be issued in the Affiliation.
In lieu thereof, each holder of Walden Common Stock who otherwise would have
been entitled to a fractional share of UST Common Stock will receive cash in an
amount determined by multiplying such holder's fractional interest by the
Closing Price.
 
     The "Effective Time" of the Affiliation will be the date and time at which
the Articles of Merger of Walden and Merger Subsidiary become effective, as set
forth in the Articles of Merger to be filed with the Secretary of the
Commonwealth's office of The Commonwealth of Massachusetts. The "Closing Date"
of the Affiliation will occur on the first business day after the date on which
all conditions contained in Article VI of the Affiliation Agreement are
satisfied or waived, or on such other date as the parties may agree upon. The
Closing Date, however, shall in no event take place prior to January 10, 1997.
UST and Walden have targeted the first quarter of 1997 for completion of the
Affiliation. If the Affiliation is not consummated on or before June 30, 1997,
the Affiliation Agreement may be terminated by either UST or Walden.
 
     Assuming that the number of outstanding shares of Walden Common Stock
remains unchanged from November 4, 1996, and UST stock continues to trade at
$13.81 or above, UST would issue 9,868,748 shares of UST Common Stock to acquire
5,194,078 outstanding shares of Walden Common Stock (assuming no exercise of
outstanding Walden stock options). Under such circumstances, immediately after
the Effective Time, former Walden stockholders will hold approximately 35.5% of
the outstanding shares of UST Common Stock. Based on a $17.6875 last reported
sale price for UST Common Stock as of November 4, 1996, the Affiliation would be
valued at approximately $175 million.
 
CERTAIN TERMS OF THE STOCK OPTION AGREEMENT
 
     As a condition precedent to UST's entering into the Affiliation Agreement
and the Plan of Merger, and in consideration therefor (without other
consideration or monetary payment), UST and Walden entered into a Stock Option
Agreement on August 30, 1996 (the "Stock Option Agreement"). The Stock Option
Agreement is intended to protect UST's interest under the Affiliation Agreement
upon the occurrence of certain events which may create the potential for a third
party to acquire or obtain control of Walden. The Stock Option Agreement may
discourage competing offers to acquire Walden by third parties other than UST or
a subsidiary of UST and increase the likelihood that the Affiliation will be
consummated in accordance with the terms of the Affiliation Agreement. See
"CERTAIN TERMS OF THE STOCK OPTION AGREEMENT." A copy of the Stock Option
Agreement is attached hereto as Appendix C.
 
     Pursuant to the Stock Option Agreement, Walden granted UST an option (the
"Option") to purchase, under certain circumstances and subject to adjustment, up
to 19.9% of the issued and outstanding fully paid and nonassessable shares of
Walden Common Stock at a price of $20.50 per share. The Option is exercisable
upon the occurrence of certain events that create the potential for a third
party to acquire or obtain control of Walden. In lieu of exercising the Option,
UST or any permitted transferee of UST can require Walden to repurchase, for a
formula price, the Option or any shares of Walden Common Stock purchased upon
exercise of the Option. To the best knowledge of UST and Walden, no such event
which would permit exercise of the Option has occurred as of the date hereof.
See "CERTAIN TERMS OF THE STOCK OPTION AGREEMENT."
 
DATE, TIME AND PLACE OF THE UST MEETING AND THE WALDEN MEETING
 
     The UST Meeting will be held on Tuesday, December 17, 1996 at 10:00 a.m.,
in the Auditorium located on the 12th Floor of UST's principal offices at 40
Court Street, Boston, Massachusetts 02108. The Walden Meeting will be held on
Tuesday, December 17, 1996 at 11:00 a.m., at the Westford Regency Inn and
Conference Center, 219 Littleton Road, Westford, Massachusetts.
 
                                        4
<PAGE>   18
 
PURPOSE OF THE UST MEETING AND THE WALDEN MEETING
 
     The UST Meeting.  The UST Meeting will be held for the purposes of
considering and voting on (a) a proposal to approve and adopt the Affiliation
Agreement, the Plan of Merger and the transactions contemplated thereby, (b) a
proposal to amend the UST Articles to increase the number of authorized shares
of UST Common Stock from 30,000,000 to 45,000,000 and (c) to conduct any other
business that may properly come before such meetings or any adjournments or
postponements thereof. See "THE UST MEETING -- Purpose of the Meeting" and "UST
MEETING -- ADDITIONAL MATTERS."
 
     The Walden Meeting.  The Walden Meeting will be held for the purpose of
considering and voting upon a proposal to approve and adopt the Affiliation
Agreement, the Plan of Merger and the transactions contemplated thereby, and to
conduct any other business that may properly come before such meeting or any
adjournments or postponements thereof. See "THE WALDEN MEETING -- Purposes of
the Meeting."
 
VOTE REQUIRED AT THE UST MEETING AND THE WALDEN MEETING
 
     The UST Board and the Walden Board have fixed the close of business on
November 4, 1996 as the record date (the "Record Date") for the determination of
stockholders entitled to notice of, and to vote at, the UST Meeting and the
Walden Meeting, respectively. Only the holders of record of the outstanding
shares of UST Common Stock and Walden Common Stock on the Record Date will be
entitled to notice of, and to vote at, the UST Meeting and Walden Meeting,
respectively. The presence, in person or by proxy, of the holders of a majority
in interest of all UST Common Stock or Walden Common Stock, issued, outstanding
and entitled to vote on the Record Date, is necessary to constitute a quorum at
the UST Meeting and the Walden Meeting, respectively. See "THE UST MEETING --
Record Date" and "THE WALDEN MEETING -- Record Date."
 
     UST.  The affirmative vote of the holders of at least a majority of the
shares of UST Common Stock present in person, or represented by proxy, entitled
to vote and voting at the UST Meeting is required to approve and adopt the
Affiliation Agreement, the Plan of Merger and of the transactions contemplated
thereby, including the Affiliation. The affirmative vote of the holders of at
least a majority of the shares of UST Common Stock issued, outstanding and
entitled to vote at the UST Meeting is required to amend the UST Articles with
respect to the increase in the number of authorized shares of UST Common Stock.
 
     Approval of the Affiliation Agreement by the requisite vote of the holders
of UST Common Stock is a condition to, and required for, consummation of the
Affiliation. None of the other matters being considered at the UST Meeting must
be approved by holders of UST Common Stock in order for the Affiliation to be
consummated. See "THE UST MEETING -- Votes Required to Approve the Affiliation
and Other Matters; Abstentions and Non-Votes" and "-- Ownership of UST Common
Stock by Officers and Directors."
 
     As of the Record Date, 17,936,989 shares of UST Common Stock were
outstanding and entitled to vote, of which approximately 2,709,831 shares, or
approximately 15% were held by directors and executive officers of UST, its
subsidiaries and their respective affiliates. It is expected that each such
director, officer and affiliate thereof of UST will vote the UST Common Stock
beneficially owned by him or her for approval of the Affiliation Agreement, the
Plan of Merger and the consummation of the transactions contemplated thereby.
See "THE UST MEETING -- Ownership of UST Common Stock by Officers and
Directors."
 
     Walden.  The affirmative votes of the holders of at least two-thirds of the
outstanding shares of Walden Common Stock are required to approve and adopt the
Affiliation Agreement, Plan of Merger and the transactions contemplated thereby.
Approval of the Affiliation Agreement by the requisite vote of the holders of
Walden Common Stock is a condition to, and required for, the consummation for
the Affiliation. See "THE WALDEN MEETING -- Vote Required to Approve the
Affiliation; Abstentions and Non-Votes."
 
     As of the Record Date, 5,194,078 shares of Walden Common Stock were
outstanding and entitled to vote, of which approximately 272,057 shares, or
approximately 5.24% were held by directors and executive officers of Walden, its
subsidiaries and their respective affiliates. In connection with the execution
of the Affiliation Agreement, David E. Bradbury, President, Chief Executive
Officer and Chairman of the Board of Walden, agreed in a letter to UST dated
August 30, 1996, to vote or cause to be voted all of the shares of
 
                                        5
<PAGE>   19
 
Walden Common Stock that he beneficially owns as of the Record Date in favor of
the approval of the Affiliation Agreement and the Affiliation. It is expected
that each other director, executive officer or affiliate thereof of Walden will
vote the Walden Common Stock beneficially owned by him or her for approval of
the Affiliation Agreement, the Plan of Merger and the consummation of the
transactions contemplated thereby. See "THE WALDEN MEETING -- Ownership of
Walden Common Stock by Officers and Directors."
 
RECOMMENDATIONS OF THE BOARDS OF DIRECTORS AND REASONS FOR THE AFFILIATION
 
     The UST Board and the Walden Board believe that the terms of the
Affiliation Agreement and the Plan of Merger, including the Conversion Number,
and the transactions contemplated thereby are fair and in the best interests of
UST and its stockholders and Walden and its stockholders, respectively. The
terms of the Affiliation Agreement and the Plan of Merger, including the
Conversion Number, were the result of arms' length negotiations between UST and
Walden. The Affiliation will be consummated only if approved by the requisite
vote of the holders of UST Common Stock and Walden Common Stock. See "THE
AFFILIATION -- Recommendation of the UST Board; Reasons for the Affiliation" and
"-- Recommendation of Walden Board, Reasons for the Affiliation."
 
OPINIONS OF FINANCIAL ADVISORS
 
     Fox-Pitt, Kelton, UST's financial advisor, has rendered its written
opinion, as of August 29, 1996, and as of the date of this Joint Proxy Statement
- -Prospectus, to the UST Board that, as of such dates, the Conversion Number is
fair, from a financial point of view, to UST.
 
     PaineWebber, Walden's financial advisor, has rendered its written opinion,
as of August 29, 1996, and as of the date of this Joint Proxy Statement -
Prospectus, to the Walden Board that, as of such dates, the proposed
consideration to be received by the holders of Walden Common Stock is fair, from
a financial point of view, to such holders of Walden Common Stock.
 
     The opinions of Fox-Pitt, Kelton and PaineWebber, which are attached hereto
as Appendix D and E, respectively, describe assumptions made, matters considered
and limits of the reviews undertaken by Fox-Pitt, Kelton and PaineWebber in
rendering their respective opinions, and should be read in their entirety. For
further description of the opinions of Fox-Pitt, Kelton and PaineWebber, see
"THE AFFILIATION -- Background of the Affiliation," "-- Recommendation of the
UST Board; Reasons for the Affiliation," "-- Recommendation of the Walden Board;
Reasons for the Affiliation," "-- Opinion of Financial Advisor to UST," "--
Opinion of Financial Advisor to Walden," and Appendix D and E to this Joint
Proxy Statement - Prospectus.
 
REGULATORY APPROVALS
 
     Consummation of the Affiliation requires, and the obligations of UST and
Walden under the Affiliation Agreement are conditioned upon, the receipt of the
approval of the Board of Governors of the Federal Reserve System (the "Federal
Reserve Board"), the Board of Bank Incorporation of The Commonwealth of
Massachusetts (the "Massachusetts BBI") and such other regulatory authorities as
may be required under applicable law. The Affiliation may not be consummated
until thirty days after receipt of the Federal Reserve Board approval (or
fifteen days in certain circumstances described more fully under "THE
AFFILIATION -- Regulatory Approvals Required for the Affiliation"), during which
time the United States Department of Justice (the "DOJ") may challenge the
Affiliation on antitrust grounds.
 
     Applications requesting such approvals have been or will be filed with the
Federal Reserve Board and the Massachusetts BBI. The parties' objective is to
obtain the approvals of the Federal Reserve Board and the Massachusetts BBI
during the first quarter of 1997, although no assurance can be given that any of
such approvals will be granted, and if granted, no assurance can be given that
the receipt of such approvals will occur within this time frame if at all or
that such approvals would not be conditioned in a manner which would so
materially adversely impact the economic or business benefits of the Affiliation
as to render it inadvisable in the reasonable judgment of UST, to consummate the
Affiliation. After the Effective Time, UST expects that it will apply to the
applicable bank regulatory agencies to merge the Walden bank subsidiaries with a
UST
 
                                        6
<PAGE>   20
 
bank subsidiary. Regulatory approvals of such a bank level merger are not
required for the approval of the Affiliation. See "THE AFFILIATION -- Regulatory
Approvals Required for the Affiliation" and "-- Conditions to the Consummation
of the Affiliation."
 
CERTAIN FEDERAL INCOME TAX CONSEQUENCES
 
     Consummation of the Affiliation is conditioned upon the delivery of
opinions of counsel to UST and of a tax advisor to Walden substantially to the
effect that, among other things, if consummated in accordance with the
Affiliation Agreement, the Affiliation will constitute a reorganization within
the meaning of Section 368 of the Code. If the Affiliation constitutes such a
reorganization, for federal income tax purposes: (a) no gain or loss will be
recognized by UST or by Walden as a result of the Affiliation; (b) no gain or
loss will be recognized by the stockholders of Walden upon their receipt of UST
Common Stock on conversion of their Walden Common Stock, except in respect of
cash received in lieu of fractional shares; (c) the tax basis of the shares of
UST Common Stock received by the stockholders of Walden will be the same as the
tax basis of their converted Walden Common Stock, adjusted to reflect the
Conversion Number and decreased by the tax basis allocated to any such
fractional share interests; (d) the holding period of the UST Common Stock held
by Walden stockholders will generally include the holding period of their
converted Walden Common Stock; and (e) gain or loss will be recognized by the
stockholders of Walden who dissent from the Affiliation, on their receipt of
cash in redemption of their Walden Common Stock.
 
     BECAUSE CERTAIN TAX CONSEQUENCES MAY VARY DEPENDING UPON THE PARTICULAR
CIRCUMSTANCES OF EACH WALDEN STOCKHOLDER, EACH STOCKHOLDER SHOULD CONSULT HIS OR
HER PERSONAL TAX ADVISOR AS TO THE TAX CONSEQUENCES OF THE AFFILIATION TO HIM OR
HER UNDER FEDERAL, STATE, LOCAL OR OTHER APPLICABLE LAW. See "THE AFFILIATION --
Certain Federal Income Tax Consequences."
 
ACCOUNTING TREATMENT
 
     The Affiliation, if completed as proposed, will qualify as a pooling of
interests for accounting purposes. The Affiliation Agreement provides, as a
condition to UST's obligation to consummate the Affiliation, that both UST and
Walden shall have received a letter from Arthur Andersen LLP, dated the Closing
Date, to the effect that the Affiliation qualifies for pooling of interests
accounting treatment under generally accepted accounting principles. See "THE
AFFILIATION -- Accounting Treatment."
 
EMPLOYEE MATTERS
 
     The Affiliation Agreement further provides that in the event that any
employee of Walden or any of its affiliates is transferred to UST or to any of
UST's affiliates and becomes a participant in any UST employee benefit plan,
program or arrangement, UST will grant such employee credit for the length of
service of such employee with Walden or Walden's affiliates for purposes of
eligibility to participate, vesting and eligibility for special benefits under
such UST plan, program or arrangement, but not for purposes of benefit accrual.
UST also has agreed to provide transferred employees with (i) the types of
employee benefits maintained by UST for similarly situated employees and (ii)
for a period of one year, a severance plan that is at least as favorable in the
aggregate as the plan currently maintained by Walden. Employees of Walden not
transferred to UST or any of its subsidiaries will receive all of the severance
benefits provided for under the severance plan maintained for such employees by
Walden. See "THE AFFILIATION -- Interests of Certain Persons in the Affiliation"
and "-- Indemnification and Insurance."
 
     Officers and employees with stock options outstanding at the Effective Time
under Walden stock option plans will have their options converted into options
to purchase shares of UST Common Stock in accordance with the provisions of the
Plan of Merger. See "THE AFFILIATION -- Management and Operations after the
Affiliation," "-- Interests of Certain Persons in the Affiliation," and "--
Employee Matters."
 
INTERESTS OF CERTAIN PERSONS IN THE AFFILIATION; INDEMNIFICATION AND INSURANCE
 
     Certain members of UST's management and the UST Board and Walden's
management and the Walden Board may be deemed to have certain interests in the
Affiliation above and beyond their interests as stockholders. The officers and
directors of UST and certain officers and directors of Walden will be officers
or
 
                                        7
<PAGE>   21
 
directors of UST after the Affiliation. Other executive officers of Walden will
receive severance payments according to their existing severance agreements with
Walden. UST has agreed to honor, after the Effective Time, the indemnification
policies of Walden applicable to the officers and directors of Walden with
respect to acts or omissions taken prior to the Effective Time. See "THE
AFFILIATION -- Management and Operations after the Affiliation" and "--
Interests of Certain Persons in the Affiliation."
 
     UST has also agreed to maintain for six years after the Effective Time,
Walden's existing directors' and officers' liability insurance (or substitute
policies that are at least as favorable as those provided by Walden) covering
persons who are presently covered by Walden's corresponding insurance plan. See
"THE AFFILIATION -- Indemnification and Insurance."
 
RIGHTS OF DISSENTING STOCKHOLDERS
 
     Under the Massachusetts General Laws, including in particular the
Massachusetts Business Corporation Law ("MBCL"), any Walden stockholder (i) who
files with Walden an objection to the Affiliation in writing before the approval
of the Affiliation by the stockholders of Walden and who states in such
objection that such stockholder intends to demand payment for his or her shares
if the Affiliation is concluded and (ii) whose shares are not voted in favor of
the Affiliation, shall be entitled to demand payment for his or her shares of
Walden Common Stock and an appraisal of the value thereof, in accordance with
the provisions of Sections 86 through 98 of Chapter 156B of the MBCL. UST
stockholders are not entitled to appraisal rights under the MBCL in connection
with, or as a result of, the Affiliation. See "THE AFFILIATION -- Rights of
Dissenting Stockholders" and the relevant sections of the MBCL attached hereto
as APPENDIX F.
 
COMPARATIVE RIGHTS OF STOCKHOLDERS
 
     The rights of holders of shares of UST Common Stock and Walden Common Stock
currently are each governed by the Massachusetts General Laws, including in
particular the MBCL, the UST Articles and By-laws of UST and the Articles of
Organization ("Walden Articles") and By-laws of Walden, respectively. At the
Effective Time of the Affiliation, Walden stockholders who do not exercise and
perfect their statutory dissenters' rights will become UST stockholders, and
their rights will be governed by the MBCL, the UST Articles and the By-laws of
UST. See "COMPARATIVE RIGHTS OF STOCKHOLDERS," for a discussion of differences
in the rights of the holders of Walden Common Stock and UST Common Stock.
 
CONDITIONS TO THE CONSUMMATION OF THE AFFILIATION
 
     The respective obligations of UST and Walden to consummate the Affiliation
are subject to satisfaction of a number of conditions, including (a) the receipt
of the requisite vote of the holders of UST Common Stock and Walden Common Stock
in favor of the Affiliation Agreement, the Plan of Merger and the transactions
contemplated thereby, (b) the receipt of the approval of the Affiliation by
certain Federal and state regulatory authorities, (c) the receipt by UST of the
opinion of Bingham, Dana & Gould LLP, and the receipt by Walden of the opinion
of its tax advisor Arthur Andersen LLP or other tax advisor acceptable to Walden
and UST, each opinion substantially to the effect that, if consummated in
accordance with the Affiliation Agreement, the Affiliation will be treated for
Federal income tax purposes as a reorganization within the meaning of Section
368 of the Internal Revenue Code of 1986, as amended (the "Code"), and
addressing such other matters relating to Federal income tax effects as UST or
Walden, as the case may be, may reasonably require which are customary in such
transactions, (d) the absence of any change in the business, assets, financial
condition or results of operations of Walden or any of its subsidiaries or UST
or any of its subsidiaries which has had or is reasonably likely to have a
material adverse effect on the business, results of operation or prospects of
UST or Walden, as the case may be, and its subsidiaries taken as a whole and (e)
the receipt by each of UST and Walden of a letter from Arthur Andersen, LLP, to
the effect that for financial reporting purposes, the Affiliation qualifies for
pooling of interests accounting treatment under generally accepted accounting
principles if consummated in accordance with the Affiliation Agreement.
 
     In addition, UST's obligation to consummate the Affiliation is subject to,
among other conditions, the following: (a) the termination by Walden of its 1993
Employee Stock Purchase Plan and its Deferred Compensation Plan; (b) receipt of
the Seller Affiliates Agreements (as such term is defined in the Affiliation
 
                                        8
<PAGE>   22
 
Agreement) executed by affiliates of Walden; (c) the absence of any action
having been taken by any Federal or state governmental agency or authority which
would impose any condition or restriction upon UST, Walden or any of their
subsidiaries after the Affiliation (including, without limitation, requirements
relating to the disposition of assets or limitations on interest rates) which
would so materially adversely impact the economic or business benefits of the
transactions contemplated by the Affiliation Agreement as to render inadvisable,
in the reasonable judgment of UST, the consummation of the Affiliation.
 
     Walden's obligation to consummate the Affiliation is also subject to (a)
the authorization for listing on NASDAQ of the UST Common Stock issuable in
connection with the Affiliation and (b) receipt of the Buyer Affiliates
Agreements (as such term is defined in the Affiliation Agreement) executed by
affiliates of UST. See "THE AFFILIATION -- Conditions to the Consummation of the
Affiliation."
 
CONDUCT OF BUSINESS PENDING THE AFFILIATION
 
     UST and Walden have each agreed to, and will cause their respective
subsidiaries to, undertake or refrain from undertaking certain actions pending
the Affiliation. In addition, UST and Walden have agreed to cooperate or
coordinate with each other with respect to the taking of certain actions by
either or both of them pending the Affiliation. Walden has also agreed to
conduct its business in the ordinary and usual course of business consistent
with past practice and to use all reasonable efforts to preserve its goodwill
and its business relationships including its relationships with its depositors.
For a full discussion of the provisions of the Affiliation Agreement relating to
the conduct of business of UST and Walden pending the Affiliation, see "THE
AFFILIATION -- Conduct of Business Pending the Affiliation."
 
WAIVER AND AMENDMENT
 
     Prior to the Effective Time, any provision of the Affiliation Agreement may
be waived in writing, to the extent permitted by law, by the party entitled to
the benefits of such provision. In addition, to the extent permitted by the
Massachusetts General Laws, the Affiliation Agreement may be amended at any time
upon the written agreement of Walden and UST without the approval of their
stockholders, except that any amendment which reduces the amount of or changes
the form of consideration to be delivered to the stockholders of Walden may not
be made after the Walden Meeting without requisite Walden stockholder approval.
See "THE AFFILIATION -- Waiver and Amendment."
 
MANAGEMENT AND OPERATIONS AFTER THE AFFILIATION
 
     From and after the Effective Time the UST Board will be expanded by three
members. Mr. Bradbury, presently the Chairman of the Board, President and Chief
Executive Officer of Walden, and two other individuals selected by Walden, and
approved by UST, will be elected by the UST Board as directors of UST to fill
existing vacancies on the UST Board. So long as Mr. Bradbury is a director of
UST, he will be entitled to be a member of the UST Steering Committee.
 
     The officers and directors of the Merger Subsidiary immediately prior to
the Effective Time will serve as the officers and directors of Walden after the
Effective Time of the Affiliation. At the Effective Time, subject to UST's
rights as sole stockholder of Walden and unless such bank subsidiaries merge
with UST's bank subsidiaries as provided for below, the board of directors of
the bank subsidiaries of Walden will be those directors which UST has elected to
serve as directors of such bank subsidiaries and any additional persons
designated by UST prior to the Effective Time. At the written request of UST,
Walden has agreed to take or cause to be taken all necessary actions to
effectuate the eventual mergers of each of its bank subsidiaries with a UST
banking subsidiary as soon as practicable after the Effective Time. In the event
of such merger of the bank subsidiaries, Mr. Bradbury and the two other
individuals selected by Walden and elected to the UST Board will become
directors of the surviving subsidiary bank. See "THE AFFILIATION -- Management
and Operations after the Affiliation."
 
TERMINATION OF THE AFFILIATION AGREEMENT
 
     The Affiliation Agreement may be terminated and the Affiliation abandoned
at any time prior to the Effective Time, whether before or after the requisite
approval of Walden's stockholders, under the following
 
                                        9
<PAGE>   23
 
circumstances: (a) by mutual written consent of Walden and UST authorized by
their respective Boards of Directors; (b) by either Walden or UST (i) at any
time after June 30, 1997, (ii) if any application for regulatory approval has
been denied and such denial has become final and unappealable, or (iii) if the
stockholders of UST or Walden fail to approve the Affiliation at the UST Meeting
or the Walden Meeting, respectively, provided in any such case that the
terminating party is not then in material breach of the Affiliation Agreement or
the Stock Option Agreement; (c) by the Walden Board or the UST Board (i) in the
event of a material breach by the other party of any representation, warranty,
covenant or other agreement contained in the Affiliation Agreement or Stock
Option Agreement which is not cured within 45 days' written notice to the
breaching party, or (ii) in the event that any condition necessary for
consummation of the Affiliation cannot be satisfied by June 30, 1997 provided,
in either case, that the terminating party is not then in material breach of any
representation, warranty, covenant or other agreement contained in the
Affiliation Agreement or Stock Option Agreement; or (d) by the Walden Board if
the Closing Price (as defined in "THE AFFILIATION -- Termination of the
Affiliation Agreement") is less than $13.81 and the price of UST Common Stock
has declined more than 15% relative to a certain bank stock index. However, in
the event that Walden notifies UST of its intention to exercise its termination
right pursuant to the provisions of clause (d) above, UST may choose to increase
the consideration to be paid to Walden stockholders by increasing the Conversion
Number pursuant to the formula set forth in the Affiliation Agreement in which
case the Affiliation Agreement will remain in full force and effect.
 
MARKET AND MARKET PRICES
 
     Transactions with respect to UST Common Stock and Walden Common Stock are
quoted on NASDAQ. The Affiliation Agreement provides, as a condition to Walden's
obligations to consummate the Affiliation, that the shares of UST Common Stock
issuable in connection with the Affiliation shall have been authorized for
listing on NASDAQ upon official notice of issuance. See "THE AFFILIATION --
Conditions to the Consummation of the Affiliation." The information set forth in
the table below presents: (a) the last reported sale prices for UST Common Stock
and Walden Common Stock on NASDAQ on August 29, 1996, the business day
immediately preceding the public announcement of the Affiliation, and November
4, 1996; and (b) the Walden Common Stock equivalent per share price as of August
29, 1996, and November 4, 1996, the last practicable date prior to the mailing
of this Joint Proxy Statement - Prospectus, calculated by multiplying the last
reported sale price of UST Common Stock on NASDAQ on such dates by the
Conversion Number:
 
<TABLE>
<CAPTION>
                                                                             WALDEN
                                                  UST         WALDEN       EQUIVALENT
                                                 COMMON       COMMON       PER SHARE
                   PRICE PER SHARE AT            STOCK         STOCK         PRICE
          ------------------------------------  --------      -------      ----------
          <S>                                   <C>           <C>          <C>
          August 29, 1996.....................  $ 16.25       $20.50         $30.88
          November 4, 1996....................  $17.6875      $32.375        $33.61
</TABLE>
 
     No assurance can be given as to what the market price of UST Common Stock
will be if and when the Affiliation is consummated or when the shares of UST
Common Stock are actually issued in the Affiliation.
 
                                       10
<PAGE>   24
 
                           UST CORP. AND SUBSIDIARIES
                            SELECTED FINANCIAL DATA
 
     The following table sets forth certain selected condensed historical
consolidated financial data of UST. The table is based on and should be read in
conjunction with UST's historical financial statements and notes thereto
incorporated by reference in this Joint Proxy Statement - Prospectus. See
"INCORPORATION OF CERTAIN INFORMATION BY REFERENCE." Interim unaudited data for
the nine months ended September 30, 1996 and 1995, reflect, in the opinion of
management of UST, all adjustments necessary for a fair presentation of such
data. Results of operations for the interim periods are not necessarily
indicative of the results of operations for the full year or any other interim
period.
 
<TABLE>
<CAPTION>
                                             NINE MONTHS
                                                ENDED
                                            SEPTEMBER 30,                           YEAR ENDED DECEMBER 31,
                                       -----------------------   --------------------------------------------------------------
                                          1996         1995         1995         1994         1993         1992         1991
                                       ----------   ----------   ----------   ----------   ----------   ----------   ----------
                                                     (DOLLARS AND SHARES IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)
<S>                                    <C>          <C>          <C>          <C>          <C>          <C>          <C>
RESULTS OF OPERATIONS:
Interest Income......................  $  114,391   $  110,015   $  147,969   $  132,312   $  140,628   $  157,024   $  221,493
Interest Expense.....................      44,708       38,224       52,535       40,213       47,944       68,970      134,640
                                       ----------   ----------   ----------   ----------   ----------   ----------   ----------
Net interest income..................      69,683       71,791       95,434       92,099       92,684       88,054       86,853
Provision for possible loan losses...     (18,600)      11,290       13,090       24,281       68,427       42,245       53,712
                                       ----------   ----------   ----------   ----------   ----------   ----------   ----------
Net interest income after provision
  for possible loan losses...........      88,283       60,501       82,344       67,818       24,257       45,809       33,141
Noninterest income...................      23,095       22,800       29,970       30,334       36,723       42,359       43,636
Noninterest expense..................      67,828       66,568       88,187       91,355       93,341       95,820       89,322
                                       ----------   ----------   ----------   ----------   ----------   ----------   ----------
Income (loss) before income taxes....      43,550       16,733       24,127        6,797      (32,361)      (7,652)     (12,545)
Income tax provision (benefit).......      17,251        6,274        9,169        2,051      (11,511)      (2,931)      (4,598)
                                       ----------   ----------   ----------   ----------   ----------   ----------   ----------
Income (loss) before change in
  accounting method..................      26,299       10,459       14,958        4,746      (20,850)      (4,721)      (7,947)
Cumulative effect of change in
  accounting method (a)..............                                                             750
                                       ----------   ----------   ----------   ----------   ----------   ----------   ----------
Net income (loss)....................  $   26,299   $   10,459   $   14,958   $    4,746   $  (20,100)  $   (4,721)  $   (7,947)
                                       ==========   ==========   ==========   ==========   ==========   ==========   ==========
PER SHARE DATA:
Income (loss) before accounting
  change.............................       $1.45        $0.58        $0.83        $0.27       $(1.36)      $(0.34)      $(0.58)
Net income (loss)....................        1.45         0.58         0.83         0.27        (1.31)       (0.34)       (0.58)
Cash dividends declared..............        0.21                      0.05                                                0.15
Weighted average shares..............      18,179       18,030       18,068       17,780       15,362       13,984       13,794
END OF PERIOD BALANCES:
Total assets.........................  $2,031,648   $1,888,498   $1,969,088   $1,803,232   $2,044,266   $2,178,061   $2,365,193
Loans receivable, net................   1,317,590    1,202,642    1,272,077    1,276,683    1,348,923    1,504,806    1,684,772
Reserve for possible loan losses.....      41,411       61,846       56,029       64,088       64,465       50,478       50,100
Deposits.............................   1,496,812    1,491,822    1,512,737    1,490,806    1,640,798    1,791,931    1,998,462
Funds borrowed (b)...................     314,134      207,956      243,105      168,953      240,554      220,658      204,952
Stockholders' investment.............     190,101      165,306      173,668      132,634      152,819      143,880      146,494
Shares used in book value
  calculation........................      18,066       17,849       17,995       17,763       17,498       14,037       13,903
Book value per share.................  $    10.52   $     9.26   $     9.65   $     7.47   $     8.73   $    10.25   $    10.54
CONSOLIDATED RATIOS: (c)
Net income (loss) to average assets
  (d)................................        1.77%        0.77%        0.81%        0.25%       (0.98%)      (0.21%)      (0.30%)
Net income (loss) to average
  stockholders' investment (d).......       19.53%        8.65%        9.14%        3.12%      (14.04%)      (3.20%)      (5.29%)
Stockholders' investment to total
  assets.............................         9.4%         8.8%         8.8%         7.4%         7.5%         6.6%         6.2%
Reserve for possible loan losses to
  period end loans...................         3.0%         4.9%         4.4%         5.0%         4.8%         3.4%         3.0%
                                                                                                                             not
Dividend payout ratio (d)............        14.5%                      6.0%                                              meaningful
</TABLE>
 
- ---------------
 
(a) Reflects cumulative effect of change in method of accounting for income
    taxes.
(b) Includes federal funds purchased, repurchase agreements, short-term and
    other borrowings.
(c) Results for interim periods have been annualized.
(d) Based on income before cumulative changes in accounting principle.
 
                                       11
<PAGE>   25
 
                     WALDEN BANCORP, INC. AND SUBSIDIARIES
                            SELECTED FINANCIAL DATA
 
     The following table sets forth certain selected condensed historical
consolidated financial data of Walden. The table is based on and should be read
in conjunction with Walden's historical financial statements and notes thereto
incorporated by reference in this Joint Proxy Statement - Prospectus. See
"INCORPORATION OF CERTAIN INFORMATION BY REFERENCE." Interim unaudited data for
the nine months ended September 30, 1996 and 1995, reflect, in the opinion of
management of Walden, all adjustments necessary for a fair presentation of such
data. Results of operations for the interim periods are not necessarily
indicative of the results of operations for the full year or any other interim
period.
 
<TABLE>
<CAPTION>
                                                   NINE MONTHS
                                               ENDED SEPTEMBER 30,                    YEAR ENDED DECEMBER 31,
                                              ---------------------   -------------------------------------------------------
                                                 1996        1995        1995       1994(D)      1993       1992       1991
                                              ----------   --------   ----------    --------   --------   --------   --------
                                                        (DOLLARS AND SHARES IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)
<S>                                           <C>          <C>        <C>           <C>        <C>        <C>        <C>
RESULTS OF OPERATIONS:
Interest Income.............................  $   55,820   $ 52,903   $   70,953    $ 60,311   $ 56,822     60,856     68,365
Interest Expense............................      26,543     24,484       33,027      24,618     23,609     30,626     45,079
                                              ----------   --------   ----------    --------   --------   --------   --------
Net interest income.........................      29,277     28,419       37,926      35,693     33,213     30,230     23,286
Provision for possible loan losses..........         926        775        1,025       1,200      3,000      4,730      6,994
                                              ----------   --------   ----------    --------   --------   --------   --------
Net interest income after provision for
  possible loan losses......................      28,351     27,644       36,901      34,493     30,213     25,500     16,292
Noninterest income..........................       5,049      5,309        8,728       7,668      9,426      7,344         58
Noninterest expense.........................      19,339     20,937       30,633(e)   27,778     25,355     23,454     24,537
                                              ----------   --------   ----------    --------   --------   --------   --------
Income (loss) before income taxes...........      14,061     12,016       14,996      14,383     14,284      9,390     (8,187)
Income tax provision (benefit)..............       5,206      4,575        5,697       4,895      4,513      2,655       (786)
                                              ----------   --------   ----------    --------   --------   --------   --------
Income (loss) before change in accounting
  method....................................       8,855      7,441        9,299       9,488      9,771      6,735     (7,401)
Cumulative effect of change in accounting
  method (b)................................                                                      2,000
                                              ----------   --------   ----------    --------   --------   --------   --------
Net income (loss)...........................  $    8,855   $  7,441   $    9,299    $  9,488   $ 11,771   $  6,735   $(7,401)
                                              ==========   ========   ==========    ========   ========   ========   ========
PER SHARE DATA:
Income (loss) before accounting change......       $1.65      $1.40        $1.74       $1.79      $1.87      $1.36     $(1.48)
Net income (loss)...........................        1.65       1.40         1.74        1.79       2.26       1.36      (1.48)
Cash dividends declared.....................        0.46       0.32         0.45        0.29       0.06
Weighted average shares.....................       5,377      5,322        5,352       5,289      5,214      5,032      4,993
END OF PERIOD BALANCES:
Total assets................................  $1,049,393   $982,111   $1,024,731    $977,977   $847,687   $805,542   $780,814
Loans receivable, net.......................     621,847    634,452      648,265     626,656    517,878    496,555    500,819
Reserve for possible loan losses............      11,332     11,962       12,091      11,024     10,543     10,031     11,421
Deposits....................................     759,412    785,594      769,564     764,678    692,391    700,054    706,555
Funds borrowed (c)..........................     181,325     92,881      147,324     117,848     65,706     29,461      5,511
Stockholders' investment....................      95,049     91,081       93,389      81,530     76,314     63,418     56,429
Shares used in book value calculation.......       5,115      5,183        5,261       5,128      5,060      5,001      4,987
Book value per share........................  $    18.58   $  17.57   $    17.75    $  15.90   $  15.08   $  12.68   $  11.28
CONSOLIDATED RATIOS: (f)
Net income (loss) to average assets (a).....        1.15%      1.02%        0.95%       1.04%      1.18%      0.85%     (0.93%)
Net income (loss) to average stockholders'
  investment (a)............................       12.41%     11.37%       10.58%      11.73%     13.60%     11.29%    (12.48%)
Stockholders' investment to total assets....         9.1%       9.3%         9.1%        8.3%       9.0%       7.9%       7.2%
Reserve for possible loan losses to period
  end loans.................................         1.8%       1.9%         1.9%        1.8%       2.0%       2.0%       2.3%
Dividend payout ratio (a)...................        27.9%      22.9%        28.2%       16.2%       3.2%        --         --
</TABLE>
 
- ---------------
 
(a) Based on income before cumulative effect of change in accounting principle.
(b) Reflects cumulative effect of change in method of accounting for income
    taxes.
(c) Includes federal funds purchased, repurchase agreements, short-term and
    other borrowings and subordinated debenture.
(d) Includes the operating results of the former Depositors Trust Company from
    the June 4, 1994 acquisition date.
(e) Includes nonrecurring merger related costs of $2.4 million in 1995 in
    connection with the formation of Walden.
(f) Results for interim periods have been annualized.
 
                                       12
<PAGE>   26
 
                           UST CORP. AND SUBSIDIARIES
                     WALDEN BANCORP, INC. AND SUBSIDIARIES
                   PRO FORMA COMBINED SELECTED FINANCIAL DATA
 
     The following table sets forth certain unaudited combined condensed
financial information from the Unaudited Condensed Pro Forma Combined Statements
of Income for the nine months ended September 30, 1996 and 1995 and the three
years ended December 31, 1995, 1994 and 1993, and the Unaudited Pro Forma
Condensed Combining Balance Sheet at September 30, 1996. The UST and Walden
combined results of operations gives effect to UST's proposed acquisition of
Walden as a pooling of interests, as if such transaction had been completed as
of the beginning of each of the periods indicated. The summary unaudited
financial information should be read in conjunction with the Pro Forma Financial
Information and related notes thereto presented elsewhere in this Proxy
Statement - Prospectus and the consolidated financial statements and related
notes incorporated by reference. See "INCORPORATION OF CERTAIN INFORMATION BY
REFERENCE" and "UNAUDITED PRO FORMA CONDENSED FINANCIAL INFORMATION."
 
<TABLE>
<CAPTION>
                                                          NINE MONTHS
                                                      ENDED SEPTEMBER 30,                 YEAR ENDED DECEMBER 31,
                                                   -------------------------       --------------------------------------
                                                      1996            1995           1995           1994           1993
                                                   ----------       --------       --------       --------       --------
<S>                                                <C>              <C>            <C>            <C>            <C>
                                                              (DOLLARS AND SHARES IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)
RESULTS OF OPERATIONS:(b)(c)
Interest Income..................................  $  170,211       $162,918       $218,922       $192,623       $197,450
Interest Expense.................................      71,251         62,708         85,562         64,831         71,553
                                                   ----------       --------       --------       --------       --------
Net interest income..............................      98,960        100,210        133,360        127,792        125,897
Provision for possible loan losses...............     (17,674)        12,065         14,115         25,481         71,427
                                                   ----------       --------       --------       --------       --------
Net interest income after provision for possible
  loan losses....................................     116,634         88,145        119,245        102,311         54,470
Noninterest income...............................      28,144         28,016         38,698         38,002         46,149
Noninterest expense..............................      87,167         87,412        118,820        119,133        118,696
                                                   ----------       --------       --------       --------       --------
Income (loss) before income taxes................      57,611         28,749         39,123         21,180        (18,077)
Income tax provision (benefit)...................      22,457         10,849         14,866          6,946         (6,998)
                                                   ----------       --------       --------       --------       --------
Income (loss) before change in accounting
  method.........................................  $   35,154       $ 17,900       $ 24,257       $ 14,234       $(11,079)
                                                   ==========       ========       ========       ========       ========
PER SHARE DATA:
Income (loss) before accounting change...........  $     1.24       $   0.64       $   0.86       $   0.51       $  (0.44)
Cash dividends declared..........................        0.22           0.06           0.12           0.05           0.01
Weighted average shares..........................      28,396         28,142         28,237         27,829         25,269
SEPTEMBER 30, 1996 PRO FORMA BALANCES:
Total assets.....................................  $3,725,409
Loans receivable, net of unearned................   2,382,840
Reserve for possible loan losses.................      50,360
Deposits.........................................   3,018,207
Funds borrowed (a)...............................     389,753
Stockholders' investment.........................     277,607
Shares used in book value calculation............      27,785
Book value per share.............................  $     9.99
</TABLE>
 
- ---------------
 
(a) Includes federal funds purchased, repurchase agreements, short-term and
    other borrowings and subordinated debt.
(b) The effect of an estimated $13.5 million pre-tax charge to be taken in
    connection with the proposed acquisition has not been reflected in the above
    results of operation since it is nonrecurring, nor do the pro forma results
    of operation give effect to any anticipated cost savings to be realized in
    connection with the acquisition.
(c) The effect of the purchase of twenty branches from The First National Bank
    of Boston and its parent company, Bank of Boston Corporation entered into on
    June 18, 1996 and the sale of UST's Connecticut banking subsidiary, UST
    Bank/Conn for cash are not included in the above results of operations. See
    "INFORMATION ABOUT UST -- Recent Developments" for a description of the
    Branch Purchase and the pending sale of UST Bank/Conn. See "UNAUDITED PRO
    FORMA CONDENSED FINANCIAL INFORMATION -- Notes to Pro Forma Combined
    Financial Information" for a discussion of the impact of the Branch Purchase
    and sale of UST Bank/Conn on the results of operation.
 
                                       13
<PAGE>   27
 
                               UST CAPITALIZATION
 
     The following table sets forth the capitalization of UST and its
subsidiaries at September 30, 1996, and the capitalization of UST and its
subsidiaries adjusted to give effect to the merger of Merger Subsidiary with and
into Walden. The table also gives effect to the pending purchase of twenty
branches from The First National Bank of Boston and its parent company, Bank of
Boston Corporation, entered into on June 18, 1996 (the "Branch Purchase") and
the sale of UST's Connecticut banking subsidiary, UST Bank/Connecticut
("UST/Conn") for cash pursuant to an agreement with HUBCO, Inc. entered into on
August 15, 1996. See "INFORMATION ABOUT UST -- Recent Developments" for a
description of the Branch Purchase and the pending sale of UST/Conn. This
information should be read in conjunction with the historical consolidated
financial statements of UST and Walden, including the respective notes thereto,
which are incorporated by reference in this Joint Proxy Statement - Prospectus,
and in conjunction with the Unaudited Pro Forma Condensed Combined Balance
Sheet, including the Notes thereto, appearing elsewhere in this Joint Proxy
Statement - Prospectus, and in conjunction with the Unaudited Pro Forma
Condensed Combining Balance Sheet, including the Notes thereto, appearing
elsewhere in this Joint Proxy Statement - Prospectus. See "INCORPORATION OF
CERTAIN INFORMATION BY REFERENCE" and "UNAUDITED PRO FORMA CONDENSED FINANCIAL
INFORMATION."
 
<TABLE>
<CAPTION>
                                          UST          WALDEN        PRO FORMA      BRANCH          SALE        PRO FORMA
           (IN THOUSANDS)              HISTORICAL    ADJUSTMENTS      COMBINED     PURCHASE       UST/CONN       COMBINED
                                       ----------    -----------     ----------    ---------     ----------     ----------
<S>                                    <C>           <C>             <C>           <C>           <C>            <C>
Deposits............................   $1,496,812       759,412(a)   $2,256,224    $ 860,000(c)  $ (98,017 )(d) $3,018,207
Short-term borrowings...............      314,134        79,899(a)     394,033      (100,000)(e)    (5,706 )(d)   288,327
Other borrowings....................                    101,426(a)     101,426                                    101,426
                                       ----------      --------      ----------    ---------     ---------      ----------
Total deposits and borrowings.......   $1,810,946       940,737      $2,751,683    $ 760,000     $(103,723 )    $3,407,960
                                       ==========      ========      ==========    =========     =========      ==========
Stockholders' Investment:
    Preferred stock $1 par value;
        Authorized - 4,000,000
          shares;
        Outstanding - None
    Common stock $.625 par value;
        Authorized - 30,000,000
          shares;
        Shares issued or to
        be outstanding (Note 4).....   $   11,205     $   6,074(a)   $  17,279                                  $  17,279
    Additional paid-in Capital......       74,746        (4,923)(a)    107,937                                    107,937
                                                         38,114(a)
    Retained earnings...............      108,054        56,505(a)     155,459     $  (2,820)(c) $   4,377 (d)    157,016
                                                         (9,100)(b)
    Unrealized loss on securities
        available-for-sale, net of
          tax.......................       (4,339)         (721)(a)     (5,060 )                                   (5,060 )
    Deferred compensation and
      other.........................          435                          435                                        435
                                       ----------      --------      ----------    ---------     ---------      ----------
    Total stockholders'
      investment....................   $  190,101     $  85,949      $ 276,050     $  (2,820)    $   4,377      $ 277,607
                                       ==========      ========      ==========    =========     =========      ==========
</TABLE>
 
- ---------------
 
(a) Reflects the combination of Walden deposits, borrowings and stockholders'
    investment with UST and the issuance of 1.9 shares of UST Common Stock in
    exchange for, and the cancellation of, each outstanding share of Walden
    Common Stock. The difference between the par value of the Common Stock to be
    issued ($.625 per share) and the par value of the Walden Common Stock to be
    acquired ($1.00 per share) has been charged to Additional paid-in capital.
 
(b) Reflects an estimated one-time after-tax charge of $9.1 million ($13.5
    million pre-tax), to be taken by UST in connection with the Merger, at a 40%
    tax rate, after excluding $2.5 million of nondeductible expense.
 
(c) Reflects the assumption of an estimated $860 million of deposits and an
    estimated one-time after-tax charge of $2.8 million, ($4.7 million pre-tax),
    to be taken by UST in connection with the Branch Purchase, at a 40% tax
    rate.
 
(d) Reflects the elimination of deposits and borrowings in connection with the
    sale of UST/Conn and the recognition of an estimated $6.7 million pre-tax
    gain, net of a 35% tax provision of $2.4 million which is recorded in other
    liabilities.
 
(e) Reflects a reduction in interest bearing liabilities using a portion of the
    net cash to be received in the Branch Purchase.
 
                                       14
<PAGE>   28
 
                           COMPARATIVE PER SHARE DATA
                                  (UNAUDITED)
 
     The following table shows unaudited comparative per share data for UST and
Walden on a historical and pro forma basis after giving effect to the
Affiliation, using the pooling-of-interests method of accounting. The
information should be read in conjunction with the consolidated historical
financial statements and notes thereto of UST and Walden which are incorporated
by reference in this Joint Proxy Statement - Prospectus, and the unaudited pro
forma condensed financial information, including notes thereto, which appear
elsewhere in this Proxy Statement - Prospectus. The pro forma data is presented
for comparative purposes only and is not necessarily indicative of the combined
financial position or results of operations which would have been realized had
the Affiliation been consummated during the periods or as of the dates for which
the pro forma data is presented. See "INCORPORATION OF CERTAIN INFORMATION BY
REFERENCE" and "UNAUDITED PRO FORMA CONDENSED FINANCIAL INFORMATION."
 
<TABLE>
<CAPTION>
                                               NINE MONTHS ENDED
                                                 SEPTEMBER 30,              YEAR ENDED DECEMBER 31,
                                            ------------------------    --------------------------------
                                               1996          1995         1995        1994        1993
                                            ----------    ----------    --------    --------    --------
<S>                                         <C>           <C>           <C>         <C>         <C>
PER SHARE OF UST COMMON STOCK:
Income (loss) before change in accounting
  method:
     Historical...........................    $ 1.45        $ 0.58       $ 0.83      $ 0.27      $(1.36)
     Pro forma UST and Walden.............      1.24          0.64         0.86        0.51       (0.44)
Cash dividends declared:
     Historical...........................      0.21                       0.05
Book value (as of period end):
     Historical...........................     10.52          9.26         9.65        7.47        8.73
     Pro forma UST and Walden.............      9.94          9.26         9.54        7.79        8.45
     Pro forma UST, Walden, Branch
       Purchase and sale of UST
       Bank/Connecticut...................      9.99
PER SHARE OF WALDEN COMMON STOCK:
Income (loss) before change in accounting
  method:
     Historical...........................      1.65          1.40         1.74        1.79        1.87
     Pro forma equivalent.................      2.35          1.21         1.63        0.97       (0.83)
Cash dividends declared:
     Historical...........................      0.46          0.32         0.45        0.29        0.06
     Pro forma equivalent.................      0.42          0.11         0.23        0.10        0.02
Book value (as of period end):
     Historical...........................     18.58         17.57        17.75       15.90       15.08
     Pro forma equivalent.................     18.88         17.59        18.13       14.79       16.06
     Pro forma UST, Walden, Branch
       Purchase and sale of UST
       Bank/Connecticut...................     18.98
</TABLE>
 
                                       15
<PAGE>   29
 
                                THE UST MEETING
 
DATE, TIME AND PLACE
 
     This Joint Proxy Statement - Prospectus is being furnished to holders of
UST Common Stock in connection with the solicitation of proxies by the Board of
Directors of UST for use at the UST Meeting. The UST Meeting is scheduled to be
held on Tuesday, December 17, 1996 at 10:00 a.m., in the Auditorium located on
the 12th Floor of UST's principal offices at 40 Court Street, Boston,
Massachusetts 02108.
 
PURPOSES OF THE MEETING
 
     The UST Meeting will be held for the purposes of considering and voting
upon proposals to (i) approve and adopt the Affiliation Agreement, the Plan of
Merger and each of the transactions contemplated thereby, (ii) approve the
amendment to the UST Articles to increase the number of authorized shares of UST
Common Stock from 30,000,000 to 45,000,000, and (iii) to transact such other
business as may properly come before such meeting, or any adjournments or
postponements thereof. With the exception of these matters, the management of
UST knows of no other matters at this time to be brought before the UST Meeting.
For additional information with respect to the amendment of the UST Articles,
see "UST MEETING -- ADDITIONAL MATTERS" which is included in the Joint Proxy
Statement - Prospectus to be delivered to UST stockholders only.
 
     THE UST BOARD UNANIMOUSLY RECOMMENDS THAT UST STOCKHOLDERS VOTE FOR
APPROVAL AND ADOPTION OF THE AFFILIATION AGREEMENT, THE PLAN OF MERGER AND THE
TRANSACTIONS CONTEMPLATED THEREBY AND FOR THE PROPOSED AMENDMENTS TO THE UST
ARTICLES.
 
RECORD DATE
 
     The UST Board has fixed the close of business on November 4, 1996, as the
record date (the "Record Date"). Only the holders of outstanding shares of UST
Common Stock on the Record Date are entitled to notice of, and to vote at, the
UST Meeting. As of the Record Date, there were issued and outstanding 17,936,989
shares of UST Common Stock entitled to vote. The presence, in person or by
proxy, of a majority in interest of all shares of UST Common Stock issued,
outstanding and entitled to vote as of the Record Date is necessary to
constitute a quorum at the UST Meeting.
 
PROXIES; VOTING AND REVOCATION
 
     Each common stockholder is entitled to one vote, in person or by proxy, for
each share of UST Common Stock held of record in his or her name at the close of
business on the Record Date. Shares of UST Common Stock represented by a
properly executed proxy received prior to the vote at the UST Meeting and not
revoked will be voted as directed in the proxy. If a proxy is submitted and no
direction is indicated, the proxy will be voted FOR the approval and adoption of
the Affiliation Agreement, the Plan of Merger and the transactions contemplated
thereby; FOR the amendment to the UST Articles; and in such manner as
management's proxyholders shall decide in accordance with their best judgment on
such other matters as may properly come before the UST Meeting.
 
     Any stockholder giving a proxy prior to the UST Meeting has the right to
revoke it prior to its exercise by delivering a written notice to Eric R.
Fischer, Esq., Executive Vice President, General Counsel and Clerk of UST, 40
Court Street, Boston, Massachusetts 02108, or by returning a duly executed proxy
bearing a later date, or by attending the UST Meeting, notifying the Clerk and
voting in person. Any stockholder of record attending the UST Meeting may vote
in person whether or not a proxy has been previously given, but the mere
presence (without duly notifying the Clerk) of a stockholder at the UST Meeting
will not constitute revocation of a previously given proxy. In addition,
stockholders whose shares of UST Common Stock are not registered in their own
name will need additional documentation from the record holder of such shares to
vote personally at the UST Meeting. See also "SOLICITATION OF PROXIES."
 
                                       16
<PAGE>   30
 
VOTES REQUIRED TO APPROVE THE AFFILIATION AND OTHER MATTERS; ABSTENTIONS AND
NON-VOTES
 
     The affirmative vote of the holders of at least a majority of the shares of
UST Common Stock present in person, or represented by proxy, entitled to vote
and voting at the UST Meeting is required to approve and adopt the Affiliation
Agreement, the Plan of Merger and the transactions contemplated thereby. The
affirmative vote of the holders of at least a majority of the shares of UST
Common Stock issued, outstanding and entitled to vote at the UST Meeting is
required to amend the UST Articles with respect to the increase in the number of
authorized shares of UST Common Stock. Abstentions and broker non-votes will be
treated as shares present or represented at the UST Meeting for quorum purposes.
Abstentions and broker non-votes will be disregarded with respect to the vote to
approve the Affiliation Agreement, Plan of Merger and the transactions
contemplated thereby (i.e., they will not be considered shares entitled to vote
or voted for or against this proposal). With respect to the proposal to amend
the UST Articles, both abstentions and broker non-votes will have the effect of
votes against this proposal. (A "broker non-vote" occurs when a registered
broker holding a customer's shares in the name of the broker has not received
voting instructions on a matter from the customer and is barred by stock
exchange rules from exercising discretionary authority to vote on the matter,
which the broker indicates on the proxy.) Approval of the Affiliation Agreement
by the requisite vote of the holders of UST Common Stock is a condition to and
required for the consummation of the Affiliation. None of the other matters
being considered at the UST Meeting must be approved by the holders of UST
Common Stock in order for the Affiliation to be consummated.
 
     In the event that there are not sufficient votes to approve the Affiliation
Agreement, the Plan of Merger and the transactions contemplated thereby, or any
other proposal, at the time of the UST Meeting, the persons present or named as
proxies by a stockholder may propose and vote for one or more adjournments of
the UST Meeting to permit further solicitation of proxies. The UST Meeting may
be adjourned by a majority of the votes present.
 
     In the event that the required vote for approval by the stockholders of UST
is not obtained, the Affiliation Agreement may be terminated by either Walden or
UST, provided that the terminating party is not then in material breach of the
Affiliation Agreement or Stock Option Agreement. If the Affiliation Agreement is
terminated because of the failure to obtain the requisite stockholder approval,
the Affiliation Agreement and the Plan of Merger shall become null and void and
there shall be no liability on the part of Walden or UST or their respective
officers or directors to the other, except as specifically provided in the
Affiliation Agreement attached as Appendix A to this Joint Proxy Statement -
Prospectus. See "THE AFFILIATION -- Termination of the Affiliation Agreement."
 
OWNERSHIP OF UST COMMON STOCK BY OFFICERS AND DIRECTORS
 
     As of the Record Date, 17,936,989 shares of UST Common Stock were
outstanding and entitled to vote, of which 2,709,831 shares, representing
approximately 15% of the shares issued and outstanding were beneficially owned
by directors and officers of UST and their respective affiliates. It is expected
that each such director, officer and affiliate thereof will vote the UST Common
Stock beneficially owned by him or her for approval of the Affiliation
Agreement, the Plan of Merger and each of the transactions contemplated thereby.
It has not come to UST's attention that any such officer and affiliate thereof
will vote otherwise than for approval of the Affiliation Agreement, the Plan of
Merger and each of the transactions contemplated thereby.
 
                                       17
<PAGE>   31
 
                               THE WALDEN MEETING
 
DATE, TIME AND PLACE
 
     This Joint Proxy Statement - Prospectus is being furnished to holders of
Walden Common Stock in connection with the solicitation of proxies by the Board
of Directors of Walden for use at the Walden Meeting. The Walden Meeting is
scheduled to be held on Tuesday, December 17, 1996 at 11 a.m., at the Westford
Regency Inn and Conference Center, 219 Littleton Road, Westford, Massachusetts.
 
PURPOSES OF THE MEETING
 
     The Walden Meeting will be held for the purposes of considering and voting
upon (i) a proposal to approve and adopt the Affiliation Agreement, the Plan of
Merger and the transactions contemplated thereby and (ii) such other matters as
may properly come before such meeting, or any adjournments or postponements
thereof. The Board of Directors of Walden knows of no other matters at this time
to be brought before the Walden Meeting.
 
     THE WALDEN BOARD UNANIMOUSLY RECOMMENDS THAT WALDEN STOCKHOLDERS VOTE FOR
APPROVAL AND ADOPTION OF THE AFFILIATION AGREEMENT, THE PLAN OF MERGER AND THE
TRANSACTIONS CONTEMPLATED THEREBY.
 
RECORD DATE
 
     The Walden Board has fixed the close of business on November 4, 1996, as
the record date (the "Record Date"). Only the holders of outstanding shares of
Walden Common Stock on the Record Date are entitled to notice of, and to vote
at, the Walden Meeting. As of the Record Date, there were issued and outstanding
5,194,078 shares of Walden Common Stock entitled to vote. The presence, in
person or by proxy, of a majority in interest of all shares of Walden Common
Stock issued, outstanding and entitled to vote as of the Record Date is
necessary to constitute a quorum at the Walden Meeting.
 
PROXIES; VOTING AND REVOCATION
 
     Each stockholder is entitled to one vote, in person or by proxy, for each
share of Walden Common Stock held of record in his or her name at the close of
business on the Record Date. Shares of Walden Common Stock represented by a
properly executed proxy received prior to the vote at the Walden Meeting and not
revoked will be voted as directed in the proxy. If a proxy is submitted and no
direction is indicated, the proxy will be voted FOR the approval and adoption of
the Affiliation Agreement, the Plan of Merger and the transactions contemplated
thereby, and in such manner as management's proxyholders shall decide on such
other matters as may properly come before the Walden Meeting.
 
     Any stockholder giving a proxy prior to the Walden Meeting has the right to
revoke it prior to its exercise by delivering a written notice to Josiah S.
Cushing, Clerk of Walden, 125 Nagog Park, Acton, Massachusetts 01720, or by
returning a duly executed proxy bearing a later date, or by attending the Walden
Meeting, notifying the Clerk and voting in person. Any stockholder of record
attending the Walden Meeting may vote in person whether or not a proxy has been
previously given, but the mere presence (without duly notifying the Clerk) of a
stockholder at the Walden Meeting will not constitute revocation of a previously
given proxy. In addition, stockholders whose shares of Walden Common Stock are
not registered in their own name will need additional documentation from the
record holder of such shares to vote personally at the Walden Meeting. See also
"SOLICITATION OF PROXIES."
 
VOTE REQUIRED TO APPROVE THE AFFILIATION; ABSTENTIONS AND NON-VOTES
 
     The affirmative vote of the holders of at least two-thirds of the
outstanding shares of Walden Common Stock entitled to vote at the Walden Meeting
is required to approve and adopt the Affiliation Agreement, the Plan of Merger
and the transactions contemplated thereby. Abstentions and broker non-votes will
be treated as shares present or represented at the Walden Meeting for quorum
purposes. Abstentions and broker non-votes will have the effect of votes against
the approval of the Affiliation Agreement, Plan of Merger and the transactions
contemplated thereby. (A "broker non-vote" occurs when a registered broker
holding a customer's shares in the name of the broker has not received voting
instructions on a matter from the customer
 
                                       18
<PAGE>   32
 
and is barred from exercising discretionary authority to vote on the matter,
which the broker indicates on the proxy.)
 
     In the event that there are not sufficient votes to approve the Affiliation
Agreement, the Plan of Merger and the transactions contemplated thereby, or any
other proposal, at the time of the UST Meeting, the persons present or named as
proxies by a stockholder may propose and vote for one or more adjournments of
the UST Meeting to permit further solicitation of proxies. The Walden Meeting
may be adjourned by a majority of the votes present.
 
     In the event that the required vote for approval by the stockholders of
Walden is not obtained, the Affiliation Agreement may be terminated by either
Walden or UST, provided that the terminating party is not then in material
breach of the Affiliation Agreement or Stock Option Agreement. If the
Affiliation Agreement is terminated because of the failure to obtain the
requisite stockholder approval, the Affiliation Agreement and the Plan of Merger
shall become null and void and there shall be no liability on the part of Walden
or UST or their respective officers or directors to the other, except as
specifically provided in the Affiliation Agreement attached as Appendix A to
this Joint Proxy Statement - Prospectus or as may be required by law. See "THE
AFFILIATION -- Termination of the Affiliation Agreement."
 
OWNERSHIP OF WALDEN COMMON STOCK BY OFFICERS AND DIRECTORS
 
     As of the Record Date, 5,194,078 shares of Walden Common Stock were
outstanding and entitled to vote, of which approximately 272,057 shares,
representing approximately 5.24% of the shares issued and outstanding were
beneficially owned by directors and executive officers of Walden and their
respective affiliates. In connection with the Affiliation Agreement, Mr.
Bradbury, President, Chief Executive Officer and Chairman of the Board, agreed
in a letter agreement with UST to vote all of the shares of Walden Common Stock
beneficially owned by him as of the Record Date in favor of the approval of the
Affiliation Agreement and the Affiliation, and against the approval of any other
agreement providing for a merger, acquisition, consolidation, sale of a material
amount of assets or other business combination involving Walden or any of its
subsidiaries with any person or entity other than UST or any subsidiary of UST.
It is expected that each other director, executive officer and affiliate thereof
will vote the Walden Common Stock beneficially owned by him or her for approval
of the Affiliation Agreement, the Plan of Merger and each of the transactions
contemplated thereby. It has not come to Walden's attention that any director,
executive officer or affiliate thereof will vote otherwise than for approval of
the Affiliation Agreement, the Plan of Merger and each of the transactions
contemplated thereby.
 
                             INFORMATION ABOUT UST
 
     UST, a bank holding company registered with the Board of Governors of the
Federal Reserve System (the "Federal Reserve Board"), was organized as a
Massachusetts business corporation in 1967. UST is subject to examination by,
and is required to file reports with, the Federal Reserve Board and the
Commissioner of Banks of The Commonwealth of Massachusetts (the "Massachusetts
Commissioner"). The UST's banking subsidiaries are USTrust and United States
Trust Company ("USTC"), each headquartered in Boston, Massachusetts and each a
Massachusetts commercial bank, and UST Bank/Connecticut ("UST/Conn"),
headquartered in Bridgeport, Connecticut, a Connecticut commercial bank. See
"Recent Developments" with respect to the pending sale of UST/Conn. All of the
common stock of USTrust, USTC and UST/Conn is issued to and owned by UST. In
addition, UST owns, indirectly through its banking subsidiaries, all of the
outstanding stock of four active nonbanking subsidiaries, all Massachusetts
corporations: UST Leasing Corporation, UST Capital Corp., UST Securities Corp.
and JSA Financing Corporation.
 
     UST engages in one line of business: that of providing a broad range of
financial services through its banking and nonbanking subsidiaries principally
to individuals and small- and medium-sized companies in New England including
those located in low- and moderate-income neighborhoods within UST's defined
Community Reinvestment Act assessment area. In addition, an important component
of UST's financial services is the provision of trust and money management
services to professionals, corporate executives, nonprofit organizations, labor
unions, foundations, mutual funds and owners of closely-held business most of
whom are located in the New England region.
 
                                       19
<PAGE>   33
 
     As of the close of business on December 31, 1995, UST's total assets were
approximately $1.97 billion and USTrust, the lead bank subsidiary, had over
$1.86 billion, or 94 percent of UST's consolidated assets.
 
RECENT DEVELOPMENTS
 
     On October 15, 1996, UST reported net income of $12.9 million, or $0.71 per
share, for the quarter ended September 30, 1996, compared with net income of
$4.1 million, or $0.23 per share, for the same period of 1995. For the nine
months ended September 30, 1996, net income was $26.3 million, or $1.45 per
share, compared with $10.5 million, or $0.58 per share for the first nine months
of 1995. Net income for the third quarter of 1996 was influenced by two
significant factors. First, UST recorded a $14.6 million earnings credit through
the provision for possible loan losses, which added significantly to both third
quarter and year-to-date net income. Second, UST recorded a $3.0 million charge
against earnings to reflect UST's liability for a one-time assessment on certain
deposits insured by the Savings Association Insurance Fund, a direct result of
federal legislation enacted during the third quarter. Nonperforming assets at
September 30, 1996, consisting of nonaccrual loans, restructured loans, accruing
loans greater than ninety days past due, and other real estate owned, were $31.3
million. Losses of $1.0 million were charged against the loan losses reserve
during the quarter and recoveries on loans previously charged-off totaled $1.6
million and, at quarter end, the reserve balance was $41.4 million, equal to 140
percent of nonaccrual loans and 3.0 percent of total loans.
 
     On June 18, 1996, UST announced that its principal banking subsidiary,
USTrust, had entered into a definitive agreement with The First National Bank of
Boston and its parent company, Bank of Boston Corporation, pursuant to which
USTrust agreed to purchase certain assets and assume certain liabilities in
connection with the acquisition of a total of twenty branches of The First
National Bank of Boston and BayBank, N.A., located in the greater Boston area
(the "Branch Purchase"). The transaction includes the assumption of
approximately $860 million of deposits and the purchase of approximately $510
million in commercial, residential real estate and other loans with businesses
and consumers. Upon completion of the transaction, USTrust will pay a premium
equal to 7 percent of the deposit liabilities assumed or approximately $60
million. The transaction is expected to be completed in the fourth quarter of
1996. USTrust has applied for and received the approval of the FDIC and the
Massachusetts Commissioner to consummate the transaction. As a condition to the
FDIC approval however, USTrust must have a Tier 1 Capital Ratio of not less than
(a) 4.8%, no later than ten days after consummation of the acquisition of the
sixteen BayBank branches to be acquired (as distinguished from the consummation
of the acquisition of the four branches of The First National Bank of Boston);
and (b) 5%, no later than three months after consummation of the acquisition of
the BayBank branches and for a period of six months thereafter. See "CERTAIN
REGULATORY CONSIDERATIONS -- Dividends." In order to fund this transaction, UST
plans to inject excess capital funds from the parent and affiliate companies
into USTrust, recapture a sizeable portion of the bank's loan loss reserve to
capital and sell UST/Conn. See "CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING
INFORMATION."
 
     On August 15, 1996, UST entered into a definitive agreement to sell its
Connecticut banking subsidiary, UST/Conn to HUBCO, Inc., a New Jersey based bank
holding company. At the completion of the transaction, which is expected to
occur in the fourth quarter of 1996 or the first quarter of 1997, UST/Conn will
be merged with and into HUBCO's subsidiary, Lafayette American Bank and Trust
Company of Bridgeport, Connecticut. The Agreement and Plan of Merger provides,
among other matters, that UST will receive cash in an amount equal to UST/Conn's
Adjusted Tier 1 Capital, as defined in the agreement, plus a deposit premium of
7 percent. This transaction is subject to the approval of the FDIC and the
Connecticut Department of Banking. Assuming consummation of the Affiliation and
all of the foregoing transactions, including the Branch Purchase, it is
anticipated that UST would become a $3.7 billion bank holding company, which,
through its bank subsidiaries, will own 65 branches in the greater Boston area.
See "CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING INFORMATION."
 
     In September 1996, legislation was enacted by Congress providing for the
recapitalization of the Savings Association Insurance Fund ("SAIF"). Savings
associations and commercial banks holding SAIF-insured deposits will be assessed
a one-time charge in connection with the servicing of the debt incurred in
connection with the thrift bailout through the issuance of FICO bonds. As a
commercial bank holding SAIF-insured deposits which USTrust indirectly acquired
through affiliates on September 7, 1990, when it assumed certain
 
                                       20
<PAGE>   34
 
deposits and liabilities of the failed Home Owners Federal Loan Bank, FSB, from
the Resolution Trust Company, USTrust has accrued a one-time charge of $3
million during the quarter ended September 30, 1996, to be paid by December 31,
1996.
 
     For more information about UST, reference is made to the UST Annual Report
on Form 10-K for the year ended December 31, 1995, which is incorporated herein
by reference. See "AVAILABLE INFORMATION" and "INCORPORATION OF CERTAIN
INFORMATION BY REFERENCE."
 
                            INFORMATION ABOUT WALDEN
 
     Walden, a banking holding company registered with the Federal Reserve
Board, was organized as a Massachusetts business corporation in June 1995 for
the purpose of serving as the holding company of Concord, a Massachusetts
chartered co-operative bank, and Braintree, a Massachusetts chartered savings
bank (collectively, the "Walden Banks") upon the acquisition of the capital
stock of the Walden Banks by Walden.
 
     Concord has eight full service retail banking offices located in Middlesex
county. Braintree has eight full service offices and one limited service office
in Norfolk and Plymouth counties. Through these offices, the Walden Banks offer
a full range of commercial and retail banking products and services and conduct
other business permissible for Massachusetts banks. The Walden Banks' lending
operations focus on commercial and small business lending, commercial real
estate loans, residential construction loans, residential first mortgages, home
equity lines of credit and consumer loans.
 
     Concord has three active subsidiaries: Walden Financial Corporation,
Builders Collaborative Inc. and Walden Securities Corporation, Inc. Braintree
has three active subsidiaries: Braintree Savings Corporation, Bra-Prop
Corporation and Braintree Securities Corporation. The primary line of business
of both Builders Collaborative Inc. and Braintree Savings Corporation is the
ownership and management of real properties owned by the Walden Banks. Walden
Financial operates as a leasing company, leasing depreciable equipment and
buildings to the Walden Banks. Walden Securities Corporation, Inc., Bra-Prop
Corporation and Braintree Securities Corporation were established solely for the
purpose of acquiring and holding security investments and limited partnerships
which are permissible for banks under Massachusetts law.
 
     The Walden Banks' business activities are concentrated in Eastern
Massachusetts. All retail banking activity is conducted through the banking
offices. Lending operations, particularly loan originations, are conducted from
the retail offices and at the point of sale. Neither of the Walden Banks nor any
of their subsidiaries conduct business on a national or international basis.
 
RECENT DEVELOPMENTS
 
     On October 10, 1996, Walden reported net income of $3.0 million, or $0.58
per share, for the quarter ended September 30, 1996, compared with net income of
$2.6 million, or $0.49 per share for the same period of 1995. For the nine
months ended September 30, 1996, net income was $8.9 million, or $1.65 per
share, compared with $7.4 million, or $1.40 per share, for the first nine months
of 1995. Nonperforming assets at September 30, 1996 were $8.8 million, or .83
percent of total assets. The reserve for possible loan losses was $11.3 million,
or 1.79 percent of total loans.
 
     For more information about Walden, reference is made to the Walden Annual
Report on Form 10-K for the year ended December 31, 1995, which is incorporated
herein by reference. See "AVAILABLE INFORMATION" and "INCORPORATION OF CERTAIN
INFORMATION BY REFERENCE."
 
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<PAGE>   35
 
                                THE AFFILIATION
 
                                 (PROXY ITEM 1)
 
GENERAL
 
     Each of the UST Board and the Walden Board has unanimously approved the
Affiliation Agreement and Plan of Merger and believes that the terms of the
Affiliation are fair and in the best interests of the respective parties and
their respective stockholders, and each unanimously recommends that its
respective stockholders vote to approve and adopt the Affiliation Agreement, the
Plan of Merger and the consummation of the transactions contemplated thereby.
 
     This section of the Joint Proxy Statement - Prospectus describes certain
aspects of the proposed Affiliation, including the principal provisions of the
Affiliation Agreement and Plan of Merger. The following description of the
Affiliation does not purport to be complete and is qualified in its entirety by
reference to the Affiliation Agreement, the Plan of Merger and the Stock Option
Agreement which are attached as APPENDIX A, B and C, respectively, to this Joint
Proxy Statement - Prospectus and are incorporated herein by reference. All
stockholders of UST and Walden are urged to read the Affiliation Agreement, the
Plan of Merger and the Stock Option Agreement in their entirety.
 
BACKGROUND OF THE AFFILIATION
 
     UST.  Throughout 1994 and 1995, the primary focus of UST's executive
management was the continued improvement of the asset quality of UST and the
removal of the bank regulatory enforcement agreements previously entered into by
UST. As these goals were being realized, the UST Board and UST's executive
management, assisted by outside financial advisors, analyzed the range of
strategic options available to UST, one of which was a program of making
acquisitions in the Boston banking market to increase the value of the UST
franchise. Executive management, together with the UST Steering Committee, then
began to refine this alternative and, in connection with developing a
value-accretive strategy, identified likely acquisition or merger candidates
where a combination with UST, in the opinion of executive management, would be
an enhancement to the franchise of UST. After identifying these potential
companies, Mr. Finnegan, President and Chief Executive Officer of UST, initiated
preliminary conversations with a number of them. Included among the companies
identified as being possible and attractive acquisition or merger candidates was
Walden. However, Walden was not contacted by UST at that time.
 
     In June of 1996, Bank of Boston Corporation ("BKBC") communicated to UST
its interest in selling $860 million in deposits attributed to 20 branch offices
located in the greater Boston area of The First National Bank of Boston and
BayBank, N.A. Consistent with its accretion strategy of developing the UST
franchise, on June 18, 1996, UST caused USTrust to enter into the Branch
Purchase.
 
     In the middle of July 1996, Mr. Finnegan and Mr. Bradbury, President, Chief
Executive Officer and Chairman of the Board of Walden had a preliminary
conversation in which Mr. Finnegan expressed UST's interest in the possibility
of a combination with Walden.
 
     A number of meetings and conversations between Mr. Finnegan and Mr.
Bradbury followed through the latter part of August. At those meetings and in
those conversations, issues relating to the price of an acquisition and the
financially related terms and characteristics were discussed directly between
Messrs. Finnegan and Bradbury. Similar conversations were conducted through the
financial advisors of each of UST and Walden. Based on their previous meetings,
conversations and independent analysis of the possibilities, in a telephone
conversation on August 23, 1996, the parties discussed a stock-for-stock
conversion number and a walk-away privilege that Walden could assert if the
price of UST Common Stock declined beyond a certain measurable amount to be
determined from UST's then current trading price.
 
     Messrs. Finnegan and Bradbury then agreed that UST and Walden should
conduct reciprocal due diligence investigations and should make all efforts to
agree on and to document the terms of a possible transaction. Representatives of
and advisors to UST and Walden met on August 26 and reviewed of all of the
 
                                       22
<PAGE>   36
 
substantive elements of a possible transaction. Through August 27 and August 29,
the parties negotiated the terms of the definitive agreements.
 
     On Wednesday, August 29, a special meeting of the UST Board was convened.
All members of the UST Board were present in person or by telephonic means.
Executive management made detailed presentations to the UST Board outlining the
terms of a proposed transaction with Walden and describing its potential effects
on UST. At the meeting, the financial advisor of UST, Fox-Pitt, Kelton,
presented a detailed analysis of the financial effects of the proposed
transaction and delivered its opinion that the Conversion Number, from a
financial point of view, is fair to UST. See "THE AFFILIATION -- Opinion of
Financial Advisor to UST." At the meeting, the UST Board conducted a thorough
review of the results of UST's due diligence review of Walden, compared, with
the assistance of UST's legal and financial advisors, the proposed transaction
to similar recent transactions and assessed the conformity of the proposed
transaction with UST's earnings-accretive strategic plan. UST's special legal
advisor described the terms and structure of the transaction. After lengthy
discussion, the UST Board unanimously voted to approve the proposed transaction.
Representatives of UST and Walden then reconvened in the evening of Wednesday,
August 29, and continued their negotiation of the terms of the definitive
documentation. Additional issues relating to the structure of the Stock Option
Agreement and remaining issues in the Affiliation Agreement were then resolved,
and the parties executed the definitive Affiliation Agreement, dated as of
August 30, 1996.
 
     Walden.  Historically, prior to the formation of Walden and its acquisition
of Concord and Braintree, Concord pursued a strategy of growth through
acquisitions. In pursuit of this strategy, Concord periodically engaged in
general discussions with various Massachusetts financial institutions regarding
possible acquisitions. These discussions resulted in the 1995 formation of
Walden and combination with Braintree, the 1987 acquisition of the Quincy
Co-operative Bank, headquartered in Quincy, Massachusetts, and the 1994
acquisition of Depositors Trust Company of Lexington, Massachusetts. In
addition, Concord acquired the Randolph Co-operative Bank of Randolph,
Massachusetts, in 1989 with regulatory assistance. Until the events that led to
the proposed affiliation of Walden with UST, Walden's strategy had been to
operate Concord and Braintree as independent, community-based commercial banks.
 
     In mid-July 1996, Mr. Finnegan, contacted Mr. Bradbury, regarding a
possible business combination. At approximately the same time, Mr. Bradbury
received an unrelated inquiry from an executive of another bank holding company
regarding a possible acquisition of Walden. Mr. Bradbury indicated to both Mr.
Finnegan and the executive of the other bank holding company that, while Walden
was not actively seeking to be acquired, he would meet with each of them to
discuss their ideas, and, if the terms of any proposal were sufficiently
compelling, he would present it to the Walden Board for evaluation. Mr. Bradbury
did not inform Mr. Finnegan of the other executive's inquiry or the other
executive of Mr. Finnegan's inquiry. At its regular meeting on July 17, 1996,
the Walden Board considered the inquiries and authorized management to meet with
Mr. Finnegan and the executive of the other bank holding company.
 
     In late July, Mr. Bradbury met with Mr. Finnegan, and they discussed the
compatibility of the businesses of Walden and UST, general terms of a possible
stock-for-stock business combination transaction and potential financial
characteristics of a combined entity. Mr. Bradbury indicated that UST's
estimates regarding potential future earnings and cost savings attributable to
Walden appeared too conservative, and the two executives agreed to continue
considering the topics they had discussed, including UST's earnings and savings
assumption, and to meet again within a week or so for further discussions. When
Mr. Bradbury met with the executive of the other bank holding company, the
executive expressed a desire to enter into discussions regarding a possible
acquisition of Walden, but only on an exclusive basis whereby Walden would have
discussions only with his bank holding company and not with any other
institution. Mr. Bradbury indicated that he did not expect the Walden Board to
agree to enter into exclusive discussions, and the executive of the other bank
holding company indicated that he was not sure whether he would proceed on a
nonexclusive basis. No future meeting was discussed, and no further discussions
were planned.
 
     In early August, UST forwarded to Walden for review certain assumptions
used by UST in preparing its estimates regarding potential future earnings and
cost savings on a pro forma basis assuming a combination of Walden and UST.
After reviewing UST's assumptions, Walden concluded that UST would require
access to
 
                                       23
<PAGE>   37
 
confidential nonpublic information regarding Walden in order to correct the
assumptions, so Walden and UST entered into a confidentiality agreement, and
provided certain nonpublic information to each other and then agreed to meet
again, with their respective chief financial officers. At this meeting, the
representatives of Walden and UST compared and discussed budget estimates,
potential cost savings and terms of comparable recent combination transactions.
Based on these discussions, it was agreed that Walden and UST and their
respective financial advisors would all meet for further discussions with
respect to potential financial characteristics of a combination of Walden and
UST. Shortly after this meeting, Messrs. Bradbury and Finnegan had a long
discussion regarding certain nonfinancial aspects of a combination, including
issues with respect to officer and employee retention and severance,
representation on the UST Board and continuity of Walden's community support in
the areas served by Concord and Braintree. When Walden and UST and their
respective financial advisors met, they discussed in detail Walden's financial
statements and business strategies and potential financial characteristics of a
combined Walden and UST. Thereafter, the executive of the other bank holding
company that had expressed an interest in acquiring Walden contacted Mr.
Bradbury and indicated that he would be willing to have discussions on a
nonexclusive basis regarding a possible acquisition of Walden in a
cash-for-stock transaction, and Mr. Bradbury informed him that he would inform
the Walden Board of his interest.
 
     On August 15, 1996, Walden's management presented to the executive
committee of the Walden Board a summary of its discussions with UST and the
expression of interest from the other bank holding company, and the committee
authorized management to continue the discussions with UST while remaining
receptive to any further inquiries from the other bank holding company that had
expressed an interest in acquiring Walden. Thereafter, numerous discussions were
held between representatives of Walden and UST on a range of issues with respect
to a possible business combination, including various terms and conditions of a
possible transaction. In particular, the parties and their financial advisors
held in depth discussions regarding the ratio for determining the number of
shares of UST Common Stock to be issued in exchange for the outstanding shares
of Walden Common Stock, including what the ratio should be and whether the ratio
should be fixed or subject to adjustment in various circumstances. Based on the
progress of the discussions, Walden then authorized UST to conduct a due
diligence examination of its business and operations, and Walden and UST
authorized their respective legal counsels to commence negotiation of the
Affiliation Agreement, the Plan of Merger and related agreements. During this
period, the executive of the other bank holding company from time to time
contacted Mr. Bradbury and indicated his continued interest in a possible
acquisition of Walden in a cash-for-stock or a cash/preferred stock-for-stock
transaction, and each time Mr. Bradbury informed him that he would inform the
Walden Board of his interest.
 
     On August 28 and 29, 1996, the Walden Board held special meetings in which
representatives of Walden's management, financial advisor and special legal
counsel participated. Walden's management reported in detail the course and
results of its discussions with both UST and the other bank holding company that
had expressed an interest in acquiring Walden and its observations and
conclusions regarding the relative compatibility of UST and the other bank
holding company with Walden and the relative terms and conditions of a possible
business combination with UST or the other bank holding company with Walden,
with it being understood that management was continuing the discussions with UST
while remaining receptive to any further inquiries from the other bank holding
company. Walden's financial advisor presented detailed historical and pro forma
information regarding the historical results of operations, current financial
condition and future business prospects of Walden, UST and the other bank
holding company, as well as detailed analyses of the value of Walden, and the
consideration assumed to be received by stockholders of Walden. On August 29,
1996, Walden's financial advisor advised the Walden Board that, on the basis of
and subject to its analyses, it was of the opinion that the proposed
consideration to be received by the stockholders of Walden from UST pursuant to
the Affiliation was fair to such stockholders from a financial point of view
(for additional information, see "-- Opinion of Financial Advisor to Walden").
Walden's special legal counsel presented a detailed analysis of the draft
Affiliation Agreement, Plan of Merger and related agreements and provided an
overview of the proposed Affiliation and the process from the execution of the
agreement through the closing of the transaction. Walden's management, financial
advisor and special legal counsel responded to questions and contributed to the
Walden Board's discussions concerning the proposed agreements and transactions.
Upon the completion of its deliberations, on August 29, 1996, the board
unanimously approved
 
                                       24
<PAGE>   38
 
and adopted the Affiliation Agreement, the Plan of Merger and the Stock Option
Agreement and the transactions contemplated thereby, including the Affiliation
with UST. The Agreement was executed as of August 30, 1996.
 
RECOMMENDATION OF THE UST BOARD; REASONS FOR THE AFFILIATION
 
     The terms of the Affiliation Agreement and the Plan of Merger, including
the Conversion Number, were the result of arms' length negotiations between UST
and Walden. The UST Board determined that strategic combination with Walden on
the terms negotiated with Walden is fair and in the best interests of UST and
its stockholders as it is expected to be value-accretive to the UST franchise.
The Affiliation would continue UST's expansion of its metropolitan franchise by
adding branches in the counties of Middlesex, Norfolk and Plymouth. The UST
Board also concluded that substantial benefits to UST's other constituencies,
including its employees and the communities it serves, as well as its
stockholders, would result from the enhanced strength and diversity of the
combined company.
 
     In reaching its determination to enter into the Affiliation Agreement, the
UST Board considered a number of factors, including the following: (i) the UST
Board's familiarity with and review of UST's business, operations, financial
condition, earnings and prospects; (ii) the UST Board's review, based in part on
a presentation by UST management regarding its due diligence of Walden, Walden's
business, operations, earnings and financial condition on an historical,
prospective and pro forma basis, and the enhanced opportunities for growth that
the Affiliation makes possible; (iii) a variety of factors affecting and
relating to the overall strategic focus of UST, including, without limitation,
opportunities for growth in deposits, assets and earnings, and opportunities
available to UST in the market areas where Walden conducts business; (iv) the
current and prospective economic environment facing financial institutions,
including UST; (v) the terms of the Affiliation Agreement, the Stock Option
Agreement and the other documents executed in connection with the Affiliation;
and (vi) the anticipated cost savings and efficiencies available from the
Affiliation. The UST Board did not assign any specific or relative weight to the
factors in its consideration.
 
     THE UST BOARD UNANIMOUSLY RECOMMENDS THAT THE AFFILIATION AGREEMENT, THE
PLAN OF MERGER AND THE TRANSACTIONS CONTEMPLATED THEREBY BE APPROVED BY THE
STOCKHOLDERS OF UST.
 
RECOMMENDATION OF THE WALDEN BOARD; REASONS FOR THE AFFILIATION
 
     The Walden Board considered the Affiliation and the terms of the
Affiliation Agreement and the Plan of Merger, including the consideration to be
received by Walden's stockholders in the Affiliation, in light of economic,
financial, legal, social and market factors and concluded that the Affiliation
is in the best interests of Walden. The terms of the Affiliation Agreement are
the result of arms' length negotiations between Walden and UST, as well as
consultations between Walden and its financial advisor and special legal
counsel. Among the factors considered by the Walden Board were the historical
operating results, current financial condition, business and management and
future financial and other prospects of Walden and UST and the advice of
PaineWebber as to the fairness to Walden's stockholders, from a financial point
of view, of the consideration to be received by them in the Affiliation. Also
considered were the relative size and geographic market areas of Walden and UST,
the employment and severance policies of UST and UST's demonstrated commitment
to meeting the banking needs of the members of the communities it serves. The
Walden Board believes that the Affiliation will afford Walden's stockholders the
benefit of UST's larger market capitalization and the more liquid market for UST
Common Stock and will offer enhanced opportunities for the resulting subsidiary
banks of UST to meet the banking needs of customers and other members of the
communities currently served by Concord and Braintree.
 
     THE WALDEN BOARD UNANIMOUSLY RECOMMENDS THAT THE AFFILIATION AGREEMENT, THE
PLAN OF MERGER AND THE TRANSACTIONS CONTEMPLATED THEREBY BE APPROVED BY THE
STOCKHOLDERS OF WALDEN.
 
                                       25
<PAGE>   39
 
OPINION OF FINANCIAL ADVISOR TO UST
 
     Fox-Pitt, Kelton has acted as financial advisor to UST in connection with
the Affiliation. In connection with such engagement, at the August 29, 1996
meeting of the UST Board, Fox-Pitt, Kelton delivered its oral and written
opinion to the UST Board, to the effect that, based upon and subject to various
considerations set forth in such opinion, as of August 29, 1996, the Conversion
Number was fair, from a financial point of view, to UST. Fox-Pitt, Kelton
subsequently confirmed its August 29, 1996, opinion by delivery to the UST Board
of a written opinion dated the date of this Joint Proxy Statement-Prospectus
that is substantially identical to the August 29, 1996 opinion. No limitations
were imposed by the UST Board upon Fox-Pitt, Kelton with respect to the
investigations made or the procedures followed by Fox-Pitt, Kelton in rendering
its opinion.
 
     THE FULL TEXT OF THE WRITTEN OPINION OF FOX-PITT, KELTON, DATED THE DATE OF
THIS JOINT PROXY STATEMENT-PROSPECTUS, WHICH SETS FORTH THE ASSUMPTIONS MADE,
MATTERS CONSIDERED AND LIMITS ON THE REVIEW TAKEN, IS ATTACHED AS APPENDIX D TO
THIS JOINT PROXY STATEMENT-PROSPECTUS. UST STOCKHOLDERS ARE URGED TO READ THIS
OPINION CAREFULLY AND IN ITS ENTIRETY. FOX-PITT, KELTON'S OPINIONS ARE DIRECTED
ONLY TO THE FAIRNESS OF THE CONVERSION NUMBER TO UST FROM A FINANCIAL POINT OF
VIEW, HAVE BEEN PROVIDED TO THE UST BOARD IN CONNECTION WITH ITS EVALUATION OF
THE AFFILIATION AND DO NOT CONSTITUTE A RECOMMENDATION TO ANY UST STOCKHOLDER AS
TO HOW SUCH STOCKHOLDER SHOULD VOTE. THE SUMMARY OF THE OPINIONS OF FOX-PITT,
KELTON SET FORTH IN THIS JOINT PROXY STATEMENT-PROSPECTUS IS QUALIFIED IN ITS
ENTIRETY BY REFERENCE TO THE FULL TEXT OF SUCH OPINIONS.
 
     In arriving at its opinions, Fox-Pitt, Kelton among other things, (i)
reviewed and analyzed certain publicly available financial statements for UST
and Walden, (ii) analyzed certain internal financial statements, including
financial projections and other financial and operating data prepared by the
managements of UST and Walden, (iii) discussed the past, present and future
operations, financial condition and prospects of UST and Walden with senior
executives of the respective companies, (iv) reviewed the reported prices and
trading activity of UST Common Stock and Walden Common Stock, (v) compared the
financial performance and condition of UST and Walden and the reported prices
and trading activity of UST Common Stock and Walden Common Stock with that of
certain other comparable publicly traded companies, (vi) reviewed and discussed
with senior executives of UST and Walden the strategic objectives of the
Affiliation and the synergies and certain other benefits of the Affiliation to
UST, (vii) reviewed the financial terms, to the extent publicly available, of
certain merger and acquisition transactions comparable, in whole or in part, to
the Affiliation, (viii) reviewed the Affiliation Agreement dated as of August
29, 1996, and (ix) performed such other analyses and investigations as Fox-Pitt,
Kelton deemed appropriate.
 
     In rendering its opinions, Fox-Pitt, Kelton assumed and relied upon,
without independent verification, the accuracy and completeness of all of the
financial and other information reviewed by Fox-Pitt, Kelton for the purposes of
providing its opinions, and did not assume any responsibility for independent
verification of such information. Fox-Pitt, Kelton did not assume any
responsibility for independent valuation of the assets and liabilities of UST or
Walden nor did it assume any responsibility for reviewing loan files or visiting
branch locations. With respect to financial projections, Fox-Pitt, Kelton
assumed that they were reasonably prepared by the respective managements of UST
and Walden on bases reflecting the best currently available estimates and
judgments of the future financial performance of UST and Walden, including
projected cost savings and operating synergies from the Affiliation. Fox-Pitt,
Kelton expresses no view as to such projections or the assumptions on which they
were based. Fox-Pitt, Kelton's opinion dated August 29, 1996, and its opinion
dated the date of this Joint Proxy Statement-Prospectus are based upon economic,
market and other conditions as they existed and could be evaluated on August 28,
1996, and November 4, 1996, respectively.
 
     The forecasts or projections furnished to Fox-Pitt, Kelton for each of UST
and Walden and estimates of synergies resulting from the Affiliation were
prepared by the respective managements of each company. As a matter of policy,
neither UST nor Walden publicly discloses internal management forecasts,
projections or estimates of the type furnished to Fox-Pitt, Kelton in connection
with its analysis of the Affiliation, and such forecasts, projections and
estimates were not prepared with a view towards public disclosure. These
forecasts, projections and estimates were based on numerous variables and
assumptions which are inherently uncertain
 
                                       26
<PAGE>   40
 
and which may not be within the control of management, including, without
limitation, factors related to the integration of UST and Walden and general
economic, regulatory and competitive conditions. Accordingly, actual results
could vary materially from those set forth in such forecasts, projections and
estimates. See "CAUTIONARY STATEMENTS REGARDING FORWARD-LOOKING INFORMATION."
 
     The following is a summary of the analyses presented by Fox-Pitt, Kelton to
the UST Board at its meeting held on August 29, 1996, in connection with the
delivery of Fox-Pitt, Kelton's August 29, 1996, opinion to the UST Board.
 
     Comparable Public Company Analysis.  Fox-Pitt, Kelton reviewed and compared
certain financial, operating and stock market performance data of Walden with
certain publicly available financial, operating and stock market performance
data of (i) ten publicly traded thrift institutions headquartered in The
Commonwealth of Massachusetts and with assets between $500 million and $1.5
billion (the "Massachusetts Thrifts") and (ii) twenty-two thrift institutions
headquartered in the States of Connecticut, Massachusetts, Maine, New Hampshire,
Rhode Island and Vermont and with assets between $500 million and $1.5 billion
(the "New England Thrifts" and together with the Massachusetts Thrifts, the
"Walden Peer Companies"). Fox-Pitt, Kelton analyzed the relative performance and
value of Walden by comparing certain publicly available financial data of Walden
with the Walden Peer Companies, including ratios of loans to deposits, deposits
to assets and equity to assets, and multiples of market price to earnings per
share, market price to estimated earnings per share in 1996, and market price to
book value.
 
     Fox-Pitt, Kelton performed a similar analysis with respect to UST.
Fox-Pitt, Kelton reviewed and compared certain financial, operating and stock
market performance data of UST with twenty-one publicly traded bank holding
companies with assets between $1.5 billion and $5 billion and headquartered in
the States of Connecticut, Delaware, Massachusetts, Maryland, Maine, New
Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Virginia, Vermont
and West Virginia and Washington, D.C. (the "UST Peer Companies"). Fox-Pitt,
Kelton analyzed the relative performance and value of UST by comparing certain
publicly available financial data of UST with the UST Peer Companies, including
ratios of loans to deposits, deposits to assets and equity to assets, and
multiples of market price to earnings per share, market price to estimated
earnings per share in 1996, and market price to book value.
 
     Comparable Transactions Analysis.  Fox-Pitt, Kelton reviewed the
consideration paid or proposed to be paid in other transactions since January
1994 involving thrift institutions with assets between $500 million and $5
billion. Specifically, Fox-Pitt, Kelton analyzed (i) nine transactions in which
the seller was headquartered in Connecticut, Massachusetts, Maine, New
Hampshire, Rhode Island and Vermont (the "New England Transactions"), and (ii)
fifty-two transactions (other than the New England Transactions and transactions
involving mergers of equals) in which the seller was headquartered anywhere in
the United States other than California (the "Nationwide Transactions"). The
ratios provided below assume a UST Common Stock price of $16 3/8 (the reported
price per share of UST Common Stock on August 28, 1996), use the reported price
per share of the seller's common stock six days prior to announcement of the
applicable transaction, and with respect to Walden use publicly available
information as of June 30, 1996. In reviewing the comparable transactions,
Fox-Pitt, Kelton examined the multiples paid relative to previous twelve month
earnings, book value, tangible book value and core deposits. This analysis
yielded the following medians for the Nationwide Transactions, medians for the
New England Transactions, and the Affiliation, respectively: (i) Price to
earnings multiples of 14.4x, 13.8x and 16.4x; (ii) Price to book value
percentiles of 150.7%, 164.6% and 170.1%; (iii) Price to tangible book value
percentiles of 163.3%, 176.2% and 197.6%; (iv) Tangible book value premium to
core deposits percentiles of 7.3%, 7.2% and 10.1%; and (v) Premium over seller
common stock price percentiles of 24.0%, 19.9% and 51.7%.
 
     Stock Trading History.  Fox-Pitt, Kelton reviewed the performance of the
per share stock prices and trading volumes of the UST Common Stock and Walden
Common Stock for various time periods. Fox-Pitt, Kelton compared the per share
stock price and trading volume of UST Common Stock to the S&P Industrials (the
"S&P 400") and to sixty-eight regional bank holding companies (the "Fox-Pitt,
Kelton Regional Bank Stock Index") and compared the per share market price and
trading volume of Walden Common Stock to the S&P 400 and to nine thrift
institutions (the "Fox-Pitt, Kelton Thrift Stock Index").
 
                                       27
<PAGE>   41
 
     Pro Forma Combination Analysis.  Fox-Pitt, Kelton analyzed certain pro
forma effects resulting from the Affiliation, based on the assumptions described
above, estimates provided by research analysts, an assumed annual cost savings
of 35% of Walden's estimated non-interest expense and an assumed tax rate of
40%. This analysis showed an initial accretion of 2.42% in earnings per share of
UST Common Stock, an initial accretion of 0.02% in book value per share of UST
Common Stock, and a dividend decrease of $0.11 per share of Walden Common Stock
or a percentage decrease of 16.88% per share. No transaction costs were taken
into account in this analysis.
 
     Dividend Discount Analysis.  Fox-Pitt, Kelton performed a dividend discount
analysis to determine a range of present values per share of Walden Common Stock
assuming Walden continued to operate as a stand-alone entity. The range was
determined by adding (i) the present value of the estimated future dividend
stream that Walden could generate over the period beginning on September 30,
1996, and ending on December 31, 2000, and (ii) the present value of the
terminal value of Walden Common Stock on December 31, 2000. To determine a
projected dividend stream, Fox-Pitt, Kelton formulated three scenarios: (i) a
slow growth scenario, (ii) a base case scenario, and (iii) an aggressive growth
scenario. Under the slow growth scenario, based on assumptions described above,
Fox-Pitt, Kelton assumed: (i) an increase in assets of 5% in 1996, 10% in 1997
and 7.5% each year from 1998 through 2000; (ii) a growth of earnings per share
of 26% in 1996, 13.25% in 1997 and 7.5% each year from 1998 through 2000, and
(iii) an increase in the dividend payout stream to 28% in 1996 and 35% in 1997
and thereafter. Under the base case scenario, based on assumptions described
above, Fox-Pitt, Kelton assumed the same dividend payout ratio but increased the
asset growth rate and the earnings per share growth rate from 7.5% to 10% each
year from 1998 to 2000. Under the aggressive growth scenario, based on
assumptions described above, Fox-Pitt, Kelton assumed the same dividend payout
ratio but increased the asset growth rate and the earnings per share growth rate
from 7.5% to 12.5% each year from 1998 to 2000.
 
     The terminal values are based upon a range of price-to-earnings multiples
consistent with the range of price-to-earnings multiples at which
similarly-sized thrift institutions have been sold in recent years (13x to 16x
previous twelve month earnings per share) and a range of discount rates (13% to
15%). Applying the foregoing multiples, discount rates and assumptions,
Fox-Pitt, Kelton determined that the fully diluted value of Walden Common Stock
ranged from approximately $25.58 to $33.11 per share under the slow growth
scenario, $27.29 to $35.36 under the base case scenario and $29.08 to $37.71
under the aggressive growth scenario.
 
     In arriving at its opinions, Fox-Pitt, Kelton performed a variety of
financial analyses, the material portions of which are summarized above. The
summary set forth above does not purport to be a complete description of the
analyses performed by Fox-Pitt, Kelton or of Fox-Pitt, Kelton's presentation to
the UST Board. The preparation of a fairness opinion is a complex analytical
process involving various determinations as to the most appropriate and relevant
methods of financial analyses and the application of those methods to the
particular circumstances and, therefore, such an opinion is not necessarily
susceptible to partial analysis or summary description. In arriving at its
opinions, Fox-Pitt, Kelton did not attribute any particular weight to any
analysis or factor considered by it, but rather made qualitative judgments as to
significance and relevance of each analysis and factor. Accordingly, Fox-Pitt,
Kelton believes that its analyses must be considered as a whole and that
selecting portions of such analyses and the factors considered by it, without
considering all such analyses and factors, could create an incomplete view of
the process underlying its analyses set forth in its opinion. With regard to the
comparable public company analysis and the comparable transactions analysis
summarized above, Fox-Pitt, Kelton selected comparable public companies on the
basis of various factors; however, no public company or transactions utilized as
a comparison is identical to UST, Walden or the Affiliation. Accordingly, an
analysis of the foregoing is not mathematical; rather, it involves complex
considerations and judgments concerning differences in financial and operating
characteristics of the comparable companies and other factors that could affect
the acquisition or public trading value of the comparable companies and
transactions to which Walden, UST and the Affiliation are being compared.
 
     Fox-Pitt, Kelton's opinions do not imply any conclusion as to the likely
trading range for the UST Common Stock following consummation of the
Affiliation, and do not address UST's underlying business decision to effect the
Affiliation. In performing its analyses, Fox-Pitt, Kelton made numerous
assumptions
 
                                       28
<PAGE>   42
 
with respect to industry performance, general business, economic, market and
financial conditions and other matters, many of which are beyond the control of
UST and Walden. Any estimates contained in such analyses are not necessarily
indicative of actual past or future results or values, which may be
significantly more or less than such estimates. Actual values will depend upon
several factors, including changes in interest rates, dividend rates, market
conditions, general economic conditions and other factors that generally
influence the price of securities. SEE "CAUTIONARY STATEMENT REGARDING
FORWARD-LOOKING INFORMATION."
 
     Fox-Pitt, Kelton is an internationally recognized investment banking firm
and was selected by UST based on Fox-Pitt, Kelton's experience and expertise.
Fox-Pitt, Kelton regularly engages in evaluation of banks and bank holding
company securities in connection with acquisitions, negotiated underwritings,
secondary distributions of listed and unlisted securities, private placements
and valuations for various other purposes. In the ordinary course of its
business, Fox-Pitt, Kelton may effect transactions, for its own account or for
the account of customers, and hold at any time a long or short position in
securities of UST or Walden.
 
     Pursuant to a letter agreement dated August 26, 1996, between UST and
Fox-Pitt, Kelton, Fox-Pitt, Kelton agreed to act as financial advisor to UST in
connection with the Affiliation. UST paid Fox-Pitt, Kelton $100,000 upon the
execution of such letter agreement and $200,000 upon the execution of the
Affiliation Agreement. UST has also agreed to pay Fox-Pitt, Kelton $500,000 upon
the consummation of the Affiliation. UST has agreed to reimburse Fox-Pitt,
Kelton for its reasonable out-of-pocket expenses, including travel, outside
legal fees and related charges, and to indemnify Fox-Pitt, Kelton and related
persons against certain liabilities, including certain liabilities under the
federal securities laws, relating to or arising out of Fox-Pitt, Kelton's
engagement.
 
OPINION OF FINANCIAL ADVISOR TO WALDEN
 
     Pursuant to an engagement letter dated November 24, 1993, Walden retained
the investment banking firm of PaineWebber Incorporated ("PaineWebber") to act
as financial advisor to Walden. At the meeting of the Walden Board on August 29,
1996, PaineWebber delivered its written opinion stating that, on and as of the
date of such opinion and based upon and subject to the assumptions described in
such opinion, the consideration to be paid to holders of Walden Common Stock in
connection with the Affiliation was fair to such shareholders from a financial
point of view. In arriving at its opinion, PaineWebber made its determination as
to the fairness from a financial point of view of the consideration to be paid
to holders of Walden Common Stock in connection with the Affiliation in light of
the financial and comparative analyses described below. In connection with the
preparation and mailing of this Joint Proxy Statement-Prospectus, PaineWebber
delivered an updated opinion dated November 5, 1996, a copy of which is included
herein as Appendix E and which is incorporated by reference herein. The updated
opinion is substantially identical to the opinion delivered to the Walden Board
on August 29, 1996, and is based on financial and comparative analyses
substantially identical to those described below. Holders of Walden Common Stock
are urged to read the updated opinion in its entirety for a description of
factors considered and assumptions made by PaineWebber in rendering its opinion.
 
     PaineWebber's opinion does not address the relative merits of the
Affiliation and any other transactions or business strategies discussed or
considered by the Walden Board as alternatives to the Affiliation or the
decision of the Walden Board to proceed with the Affiliation. No opinion is
expressed as to the price at which the securities to be issued in the
Affiliation to the shareholders of Walden may trade at any time. In rendering
the opinion, PaineWebber has not been engaged to act as agent or fiduciary of
Walden's equity holders or any other third party.
 
     In arriving at its opinion, PaineWebber has, among other things: (i)
reviewed UST's audited Annual Reports, Forms 10-K and related financial
information for the five fiscal years ended December 31, 1995, UST's Form 10-Q
and related unaudited financial information for the six months ended June 30,
1996; (ii) reviewed certain unaudited financial information for the year ended
December 31, 1995 and the nine months ended September 30, 1996, relating to UST;
(iii) reviewed Walden's audited Annual Reports, Forms 10-K, Forms F-2 and
related financial information for the five fiscal years ended December 31, 1995,
Walden's 10-Q and related unaudited financial information for the six months
ended June 30, 1996; (iv) reviewed certain unaudited financial information for
the year ended December 31, 1995 and the nine
 
                                       29
<PAGE>   43
 
months ended September 30, 1996, relating to Walden; (v) reviewed information,
including financial forecasts, relating to the business, earnings, cash flow,
assets and prospects of UST and Walden, respectively, confidentially furnished
to PaineWebber by UST and Walden; (vi) conducted discussions with members of
senior management of UST and Walden concerning their respective businesses and
prospects; (vii) reviewed historical market prices and trading activity for UST
Common Stock and Walden Common Stock and compared them with those of certain
publicly traded companies which PaineWebber deemed to be reasonably similar to
UST and Walden, respectively; (viii) compared the results of operations of UST
and Walden with that of certain companies which PaineWebber deemed to be
reasonably similar to UST and Walden, respectively; (ix) reviewed the
Affiliation Agreement and Plan of Merger; (x) compared proposed financial terms
of the Affiliation with the financial terms of certain other mergers and
acquisitions which PaineWebber deemed to be relevant; and (xi) reviewed such
other financial studies and analyses and performed such other investigations and
took into account such other matters as PaineWebber deemed necessary, including
an assessment of general economic, market and monetary conditions.
 
     As set forth in its opinion, PaineWebber relied upon the accuracy and
completeness of all information supplied or otherwise made available by Walden
and UST and from generally recognized public sources, and PaineWebber did not
assume any responsibility to independently verify such information or undertake
an independent appraisal of the assets of Walden or UST. PaineWebber did not
conduct a physical inspection of the properties and facilities of Walden or UST,
did not conduct a review of the loan files of either Walden or UST and did not
make or obtain any evaluation or appraisal of the assets or liabilities of
Walden or UST. PaineWebber relied upon the accuracy of Walden and UST's earnings
projections and possible cost savings projections as a result of the
Affiliation, and PaineWebber did not assume any responsibility to independently
verify assumptions underlying such projections. The projections confidentially
furnished to PaineWebber were prepared by the respective managements of Walden
and UST, and PaineWebber has assumed that they were reasonably prepared and
reflect good faith estimates and judgments of the managements of Walden and UST,
respectively, as to the future performance of Walden and UST. Walden and UST do
not publicly disclose internal management projections of the type provided to
PaineWebber in connection with its review of the Affiliation. Such projections
were not prepared with a view toward public disclosure. The projections were
based on numerous variables and assumptions which are inherently uncertain,
including without limitation, factors related to future economic and competitive
conditions, the future financial condition and results of operations of Walden
and UST and the future cost savings associated with the Affiliation.
Accordingly, actual results could vary significantly from those reflected in
such projections. SEE "CAUTIONARY STATEMENTS REGARDING FORWARD-LOOKING
INFORMATION." No limitations were placed by Walden or UST on the scope of
PaineWebber's review in preparing the opinion. The opinion of PaineWebber is
necessarily based upon market, economic, and other conditions as they existed
on, and can be evaluated as of, the date thereof. PaineWebber's opinion is
directed only to the Walden Board and does not constitute a recommendation to
any holder of Walden Common Stock or UST Common Stock as to how such shareholder
should vote on the Affiliation.
 
     The preparation of a fairness opinion involves various determinations as to
the most appropriate and relevant methods of financial analysis and the
application of those methods to the particular circumstances and, therefore,
such an opinion is not readily susceptible to summary description. Furthermore,
in arriving at its fairness opinion, PaineWebber did not attribute any
particular weight to any analysis or factor considered by it, but rather made
qualitative judgments as to the significance and relevance of each analysis and
factor. Accordingly, PaineWebber believes that its analyses must be considered
as a whole and that considering any portions of such analyses and of factors
considered, without considering all analyses and factors, could create a
misleading or incomplete view of the process underlying its fairness opinion. In
its analyses, PaineWebber made numerous assumptions with respect to industry
performance, general business and economic conditions and other matters, many of
which are beyond the control of Walden and UST. Any estimates contained in these
analyses are not necessarily indicative of actual values or predictive of future
results or value, which may be significantly more or less favorable than as set
forth therein. In addition, analyses relating to the value of businesses do not
purport to be appraisals or to reflect the prices at which businesses actually
may be sold.
 
                                       30
<PAGE>   44
 
     The following paragraphs summarize certain financial analyses performed by
PaineWebber in arriving at its opinion dated August 29, 1996, as to the
fairness, from a financial point of view, of the consideration to be paid to the
holders of Walden Common Stock in connection with the Affiliation. PaineWebber
presented these analyses to the Walden Board on August 28, 1996, and updated
these analyses in connection with the rendering of the updated opinion included
herein. The following does not purport to be a complete description of the
analyses performed, or the matters considered, by PaineWebber in arriving at its
opinions.
 
     Comparable Company Trading Analysis: Walden.  Using publicly available
information, PaineWebber compared certain ratios of the financial performance of
Walden to the stock market capitalization of Walden at August 23, 1996, with the
following selected Massachusetts thrifts ("Comparable Group I") deemed relevant
by PaineWebber: Abington Savings Bank; Affiliated Community Bancorp; Andover
Bancorp, Inc.; BostonFed Bancorp, Inc.; Central Co-operative Bank; First Essex
Bancorp, Inc.; Grove Bank; The Hibernia Savings Bank; Lawrence Savings Bank;
MASSBANK Corp.; Medford Savings Bank; MetroWest Bank, People's Bancshares, Inc.;
SIS Bancorp, Inc.; Somerset Savings Bank; Sandwich Co-operative Bank; and Warren
Bancorp, Inc. (for all of which June 30, 1996, financial data was used). Such
comparisons included, among others, market capitalization-to-book value ratios
(a median of 103% for Comparable Group I and 111% for Walden); market
capitalization-to-tangible-book value ratios (a median of 115% for Comparable
Group I and 129% for Walden); market
capitalization-to-latest-12-months'-earnings ratios (a median of 9.9x for
Comparable Group I and 9.2x for Walden); market
capitalization-to-estimated-1996-earnings ratios (a median of 9.6x for
Comparable Group I and 8.9x for Walden); and market
capitalization-to-estimated-1997-earnings ratios (a median of 9.2x for
Comparable Group I and 7.9x for Walden). The 1996 and 1997 earnings per share
were estimates provided by First Call (as of August 23, 1996) and Zacks
Investment Research (as of August 23, 1996).
 
     In connection with this analysis and as previously discussed, management of
Walden confidentially provided PaineWebber with information with regard to its
projected future earnings. Because of the inherent differences between the
operations of Walden and the selected companies included in Comparable Group I,
PaineWebber believes that a purely quantitative comparable company analysis
would not be particularly meaningful in the context of the Affiliation.
PaineWebber believes that an appropriate use of comparable company analysis in
this instance would involve qualitative judgments concerning differences between
the financial and operating characteristics of Walden and the selected companies
included in Comparable Group I which would affect the public trading values of
Walden and the selected companies included in Comparable Group I. These
qualitative judgments made by PaineWebber in connection with its opinion
included PaineWebber's views as to business conditions and prospects in the
various markets in which these selected companies operate and the business mix,
sources of revenue, risk profile and prospects for these selected companies.
 
     Comparable Company Trading Analysis: UST.  Using publicly available
information, PaineWebber compared certain ratios of the financial performance to
the stock market capitalization of UST at August 23, 1996, with the following
selected New England and MidAtlantic banks and thrifts ("Comparable Group II")
deemed relevant by PaineWebber: First Commonwealth Financial; Trust Company of
New Jersey; Banknorth Group, Inc.; TrustCo Bank Corp NY; Bankers Corp.;
Commonwealth Bancorp, Inc.; USBANCORP, Inc.; Northwest Savings Bank, MHC; MLF
Bancorp, Inc.; Chittenden Corporation; Reliance Bancorp, Inc.; F.N.B.
Corporation; HUBCO, Inc.; First Western Bancorp, Inc.; North Side Savings Bank;
Haven Bancorp, Inc.; Harris Savings Bank, MHC; JSB Financial, Inc.; and BT
Financial Corporation (for all of which June 30, 1996, financial data was used).
Such comparisons included, among others, market capitalization-to-book-value
ratios (a median of 142% for Comparable Group II and 144% for UST); market
capitalization-to-tangible-book-value ratios (a median of 162% for Comparable
Group II and 207% for UST); market capitalization-to-latest-12-months'-earnings
ratios (a median of 12.4x for Comparable Group II and 13.0x for UST); market
capitalization-to-estimated-1996-earnings ratios (a median of 11.4x for
Comparable Group II and 11.8x for UST); and market
capitalization-to-estimated-1997-earnings ratios (a median of 10.2x for
Comparable Group II and 9.9x for UST). The 1996 and 1997 earnings per share were
estimates provided by First Call (as of August 23, 1996), Institutional Brokers
Estimate System (as of August 15, 1996) and Zacks Investment Research (as of
August 23, 1996).
 
                                       31
<PAGE>   45
 
     In connection with this analysis and as previously discussed, management of
UST confidentially provided PaineWebber with information with regard to its
projected future earnings. Because of the inherent differences between the
operations of UST and the selected companies included in Comparable Group II,
PaineWebber believes that a purely quantitative comparable company analysis
would not be particularly meaningful in the context of the Affiliation.
PaineWebber believes that an appropriate use of comparable company analysis in
this instance would involve qualitative judgments concerning differences between
the financial and operating characteristics of UST and the selected companies
included in Comparable Group II which would affect the public trading values of
UST and the selected companies included in Comparable Group II. These
qualitative judgments made by PaineWebber in connection with its opinion
included PaineWebber's views as to business conditions and prospects in the
various markets in which these selected companies operate and the business mix,
sources of revenue, risk profile and prospects for these selected companies.
 
     Comparable Transaction Analysis.  Using publicly available information,
PaineWebber reviewed certain terms and financial characteristics of selected
Massachusetts bank and thrift merger and acquisition transactions, which
PaineWebber deemed to be comparable to the Affiliation ("Comparable Transactions
Group"). Among other financial characteristics of these transactions,
PaineWebber reviewed stock price changes prior to announcement, book value and
tangible book value multiples, earnings multiples and announced core deposit
premiums. Comparable transactions considered by PaineWebber in its analysis
consist of the following transactions (identified by buyer / seller): Peoples
Heritage Financial Group / Family Bancorp; CFX Corporation / Safety Fund
Corporation; Bank of Boston Corporation / BayBanks, Inc.; Bank of Boston
Corporation / Boston Bancorp; Chittenden Corporation / Flagship Bank and Trust
Company; Citizens Financial Group, Inc. / Quincy Savings Bank; Fleet Financial
Group, Inc. / NBB Bancorp, Inc.; Shawmut National Corporation / West Newton
Savings Bank; Bank of Boston Corporation / Pioneer Financial Cooperative Bank;
Citizens Financial Group, Inc. / Neworld Bancorp; Fleet Financial Group, Inc. /
Sterling Bancshares Corporation; Bank of Boston Corporation / BankWorcester
Corporation; Shawmut National Corporation / Peoples Bancorp of Worcester;
Citizens Financial Group, Inc. / Boston Five Bancorp, Inc.; and Bank of Boston
Corporation / Multibank Financial Corporation. The median values for these
transactions for the transaction value-to-market price one week prior to
announcement, transaction value-to-book value, transaction value-to-tangible
book value, transaction value-to-latest-12-months'-earnings per share and
announced core deposit premium ratios were 119%, 175%, 178%, 15.4x and 9.76%,
respectively, compared to 152%, 167%, 195%, 13.9x and 10.53% for Walden, based
on an exchange ratio of 1.9 shares of UST Common Stock for each share of Walden
Common Stock and a UST stock price of $16.00.
 
     In the case of the Comparable Transactions Group, PaineWebber believes that
a purely quantitative comparable transaction analysis would not be particularly
meaningful in the context of the Affiliation, because the reasons for and
circumstances surrounding each of the transactions analyzed were so diverse and
because of the inherent differences between the operations of UST, Walden and
the selected companies included in the Comparable Transactions Group.
PaineWebber believes that an appropriate use of a comparable transaction
analysis in this instance would involve qualitative judgments concerning
differences between the characteristics of these transactions and the
Affiliation which would affect the acquisition value of the acquired companies
and Walden. These qualitative judgments made by PaineWebber in connection with
its opinion included: PaineWebber's views as to the universe of potential buyers
in each of these transactions, their potential level of interest in an
acquisition of these companies and the ability of the acquirors to implement
cost savings; business conditions and prospects in various markets in which
these acquired companies operate; and the business mix, sources of revenue, risk
profile and prospects for these acquired companies.
 
     Acquiror Dilution Analysis.  Using publicly available information,
PaineWebber estimated the share price that potential acquirors ("Acquiror
Group") could pay for Walden's Common Stock, based on Walden's internally
projected 1997 earnings, without diluting the acquiror's projected 1997 earnings
per share. The Acquiror Group considered by PaineWebber in its analysis
consisted of: UST; Bank of Boston Corporation; Banknorth Group, Inc.; Chittenden
Corporation; Fleet Financial Group; KeyCorp; Peoples Heritage Financial Group,
Inc.; and Vermont Financial Services Corp. In this analysis, Walden's internally
projected 1997 earnings per share, assuming various cost savings projections
based on Walden's estimated 1997 noninterest
 
                                       32
<PAGE>   46
 
expense, were multiplied by the price-to-earnings multiple of each member of the
Acquiror Group to arrive at the maximum price per share that each member of such
group could pay without diluting their respective 1997 earnings. PaineWebber
noted that the hypothetical cost savings projections assumed in this analysis
are independent of the cost savings assumed by UST and Walden's respective
managements as related to their proposed Affiliation and therefore cannot be
used to estimate acquisition prices for Walden in the proposed Affiliation. The
cost savings projections assumed in this analysis reflect general assumptions
about cost savings that might be attainable but there can be no assurance that
any potential acquirors could achieve such savings. The savings assumed to be
achieved by the Acquiror Group depend on a variety of factors which cannot be
predicted with certainty, including the timing of the closing of the
acquisitions, the pace and success of consolidation and the future results of
operations of the new entities. PaineWebber believed that an appropriate use of
an Acquiror Dilution Analysis in this instance would involve qualitative
judgments concerning differences between the characteristics of the acquirors
which would affect the acquisition price range. These qualitative judgments made
by PaineWebber in connection with its opinion included PaineWebber's views as to
the universe of potential buyers and their ability to implement cost savings and
business synergies with Walden, and, in addition, PaineWebber's views as to the
regulatory environment, prospects in various markets in which Walden operates
and business mix, sources of revenue, and risk profile.
 
     Pro Forma Merger Analysis.  PaineWebber estimated the impact of the
proposed Affiliation on Walden's and UST's projected earnings per share for 1996
and 1997, book and tangible book value per share and pro forma dividends per
share. In connection with this analysis and as previously discussed, management
of Walden and UST confidentially provided PaineWebber with information with
regard to projected future earnings. Based on such information, and the terms of
the proposed Affiliation, PaineWebber concluded that, for UST, the Affiliation
could have a dilutive effect (before taking into account various cost savings
which could be accomplished upon consolidation of Walden and UST's operations)
on estimated earnings per share in each of 1996 and 1997 of approximately 5% and
6%, respectively, and on June 30, 1996, book value per share of approximately
5%, while having an accretive effect on June 30, 1996, tangible book value per
share of 2%. PaineWebber also concluded that, for Walden, the Affiliation could
have an accretive effect (before taking into account various cost savings which
could be accomplished upon consolidation of Walden and UST's operations) on
estimated earnings per share in 1996 and 1997 of approximately 8% and 12%,
respectively, and on June 30, 1996, book value per share of approximately 10%,
while having a dilutive effect on June 30, 1996, tangible book value per share
of approximately 4%. The proposed Affiliation became accretive to UST's 1996 and
1997 earnings per share if pre-tax cost savings of greater than approximately $5
million could be achieved.
 
     PaineWebber is an internationally recognized investment banking firm and,
as part of its investment banking activities, PaineWebber is regularly engaged
in the valuation of businesses and their securities in connection with mergers
and acquisitions, negotiated underwritings, competitive bids, secondary
distributions of listed and unlisted securities, private placements and
valuations for corporate and other purposes. The Walden Board selected
PaineWebber because of its expertise, its reputation and its familiarity with
Walden and the thrift and banking industries in general.
 
     PaineWebber has acted as financial advisor to Walden in connection with the
Affiliation. As compensation for its services in connection with the
Affiliation, Walden has agreed to pay PaineWebber a fee of 1% of the final
transaction value, payable upon consummation of the Affiliation. In addition,
Walden has agreed to reimburse PaineWebber for reasonable out-of-pocket expenses
incurred in connection with the Affiliation and to indemnify PaineWebber against
certain liabilities, including liabilities that may arise under the federal
securities laws.
 
     PaineWebber has acted as financial advisor to Walden's predecessor, The
Co-operative Bank of Concord, in connection with the Bank of Braintree
acquisition. As compensation for its services in connection with the Bank of
Braintree acquisition, Walden paid PaineWebber a fee of $350,000. In addition,
Walden reimbursed PaineWebber for reasonable out-of-pocket expenses incurred in
connection with the Bank of Braintree acquisition and agreed to indemnify
PaineWebber against certain liabilities, including liabilities that may arise
under the federal securities laws.
 
                                       33
<PAGE>   47
 
     In the ordinary course of its business, PaineWebber actively trades in the
securities of Walden for its own account and for the accounts of others and,
accordingly, may at any time hold a long or short position in such securities.
 
EFFECTIVE TIME OF THE AFFILIATION; CLOSING DATE
 
     As soon as practicable after satisfaction or waiver of all conditions to
the Affiliation under the Affiliation Agreement, UST, Merger Subsidiary and
Walden shall cause Articles of Merger complying with the requirements of the
MBCL to be filed with the Secretary of State of The Commonwealth of
Massachusetts. The date and time as of which the Articles of Merger become
effective, as set forth in the Articles of Merger, will be the "Effective Time."
The "Closing Date" will occur on the first business day after the date on which
all conditions contained in Article VI of the Affiliation Agreement are
satisfied or waived; or at such other date as the parties may agree upon. The
Closing Date, however, shall in no event take place prior to January 10, 1997.
UST and Walden have targeted the first quarter of 1997 for completion of the
Affiliation. The consummation of the Affiliation could be delayed, however, as a
result of delays in obtaining the necessary regulatory and stockholder
approvals. There can be no assurances given that such approvals will be obtained
or that the Affiliation will be completed at any time. If the Affiliation has
not been consummated on or before June 30, 1997, the Affiliation Agreement may
be terminated by either UST or Walden. See "THE AFFILIATION -- Regulatory
Approvals," "-- Conditions to the Consummation of the Affiliation," and "--
Termination of the Affiliation Agreement."
 
TERMS OF THE AFFILIATION
 
     The Affiliation Agreement and the Plan of Merger provide for the merger of
Merger Subsidiary with and into Walden, with Walden as the surviving corporation
and a wholly-owned subsidiary of UST. Upon the consummation of the Affiliation,
each outstanding share of Walden Common Stock will be converted into 1.9 shares
of UST Common Stock (the "Conversion Number"), and a corresponding amount of
preferred stock purchase rights issued pursuant to the UST Rights Agreement,
dated as of September 19, 1995 (the "UST Rights Agreement"), provided that the
following types of shares shall not be converted: (i) shares of Walden Common
Stock which are held directly or indirectly by UST unless held by UST in a
fiduciary capacity, (ii) shares of Walden Common Stock held as treasury shares
by Walden, and (iii) Dissenting Shares. Where a holder of Walden Common Stock
has shares of record represented by two or more certificates, the certificates
will be aggregated.
 
     In addition, if the Closing Price (as such term is defined in "THE
AFFILIATION --Termination of the Affiliation Agreement") is less than $13.81 per
share and the price of UST Common Stock has declined more than 15% relative to a
certain bank stock index, the Walden Board may notify UST in writing of its
intention to terminate the Affiliation Agreement. However, in the event that
Walden notifies UST of its intention to exercise its termination rights pursuant
to the foregoing sentence, UST may in the time period prescribed in the
Affiliation Agreement, choose to increase the consideration to be paid to Walden
stockholders by increasing the Conversion Number to equal the number obtained by
dividing (x) 26.24 by (y) the Closing Price, in which case the Affiliation
Agreement shall remain in full force and effect. In the event that UST exercises
its rights to increase the Conversion Number, holders of Walden Common Stock
will receive more than 1.9 shares of UST Common Stock for each share of Walden
Common Stock to compensate for a decrease in the value of UST Common Stock. For
a full discussion of UST and Walden's termination rights, see "THE AFFILIATION
- -- Termination of the Affiliation Agreement."
 
     Each outstanding share of Walden Common Stock owned by UST and its
subsidiaries (other than in a fiduciary capacity) or by Walden as treasury stock
will be cancelled and retired at the Effective Time and cease to exist, and no
payment will be made with respect thereto.
 
     Shares of Walden Common Stock held by a stockholder who has demanded
appraisal rights in compliance with the provisions of the MBCL will not be
converted into UST Common Stock at the Effective Time (see "THE AFFILIATION --
Rights of Dissenting Stockholders"). If, however, the stockholder subsequently
withdraws his or her demand for appraisal or loses his or her right of
appraisal, the stockholder's shares will be deemed to be so converted as of the
Effective Time.
 
                                       34
<PAGE>   48
 
     In addition, at the Effective Time all stock options with respect to Walden
Common Stock granted by Walden or its affiliates under any stock option plan,
which are outstanding at such time, whether or not then exercisable, will be
converted into and will become stock options with respect to UST Common Stock.
The rights to UST Common Stock to be received by holders of Walden stock options
upon consummation of the Affiliation will be identical to the rights such
optionees had under the Walden stock option plans which covered such stock
options immediately prior to the Effective Time, except that the number of
shares of UST Common Stock subject to such options and the exercise price per
share of such options will be determined in accordance with the Conversion
Number. The number of shares of UST Common Stock subject to each such stock
option will be equal to the product of the number of shares of Walden Common
Stock previously subject thereto and the Conversion Number, rounded down to the
nearest whole share. The exercise price per share of UST Common Stock shall be
equal to the exercise price per share of Walden Common Stock previously subject
thereto divided by the Conversion Number, rounded up to the nearest cent.
 
     The Affiliation Agreement provides that, in the event that UST changes the
number of shares of UST Common Stock issued and outstanding between August 30,
1996, and the Effective Time as a result of a stock split, stock dividend,
recapitalization, reclassification or other similar transaction, the Conversion
Number will be adjusted proportionately.
 
     No fractional shares of UST Common Stock will be issued in the Affiliation.
The Affiliation Agreement provides that each holder of shares of Walden Common
Stock exchanged pursuant to the Affiliation, who would otherwise have been
entitled to receive a fraction of a share of UST Common Stock (after taking into
account all certificates delivered by such holder) will receive, in lieu
thereof, cash (without interest) in an amount determined by multiplying such
holder's fractional interest by the Closing Price.
 
     Shares of UST capital stock (including UST Common Stock) issued and
outstanding immediately prior to the Effective Time will remain issued and
outstanding immediately after the Affiliation.
 
REGULATORY APPROVALS REQUIRED FOR THE AFFILIATION
 
     Federal Reserve.  The Affiliation is subject to approval of the Federal
Reserve Board under the Bank Holding Company Act of 1956, as amended (the "BHC
Act"). Assuming Federal Reserve Board Approval is granted, the Affiliation may
not be consummated until thirty (30) days after such approval, during which time
the DOJ may challenge the Affiliation on antitrust grounds and seek divestiture
of certain assets and liabilities. Because, in the opinion of UST, the
Affiliation will have no material anti-competitive effect, UST has requested,
pursuant to the BHC Act that the Federal Reserve Board recommend to the Attorney
General of the United States that the post-approval waiting period for the
Affiliation be reduced to fifteen (15) calendar days.
 
     The Federal Reserve Board is prohibited from approving any proposed
acquisition, merger, or consolidation under the BHC Act (a) which would result
in a monopoly or which would be in furtherance of any combination or conspiracy
to monopolize or to attempt to monopolize the business of banking in any part of
the United States, or (b) the effect of which in any section of the United
States may be substantially to lessen competition, or to tend to create a
monopoly, or result in a restraint of trade, unless the Federal Reserve Board
finds that the anti-competitive effects of the transaction are clearly
outweighed in the public interest by the probable effect of the transaction in
meeting the convenience and needs of the communities to be served.
 
     In making its determination with respect to the Affiliation, the Federal
Reserve Board will take into consideration the financial and managerial
resources and future prospects of the existing and proposed institutions and the
convenience and needs of the communities served. As part of, or in addition to,
consideration of the above factors, it is anticipated that the Federal Reserve
Board will consider the financial condition of UST and Walden, current and
projected economic conditions in the New England region and the overall capital
and safety and soundness standards of UST and Walden as compared to those
established by the Federal Deposit Insurance Corporation Improvement Act of 1991
("FDICIA") and the regulations promulgated thereunder.
 
                                       35
<PAGE>   49
 
     In addition, under the Community Reinvestment Act of 1977, as amended (the
"CRA"), the Federal Reserve Board must take into account the record of
performance of each of UST and Walden in meeting the credit needs of the entire
community, including low- and moderate-income neighborhoods, served by each of
such institutions. Furthermore, the BHC Act and Federal Reserve Board
regulations require publication of notice of, and the opportunity for public
comment on, the application submitted by UST for approval of the Affiliation and
the BHC Act provides that the Federal Reserve Board may permit interested
parties to intervene in the proceedings and to hold a public hearing in
connection therewith if the Federal Reserve Board determines that such a hearing
would be appropriate. Any such intervention by third parties could prolong the
period during which the application is subject to review by the Federal Reserve
Board.
 
     As noted above, the Affiliation may not be consummated until the thirtieth
day after Federal Reserve Board approval, during which time the DOJ has
jurisdiction to challenge the Affiliation on antitrust grounds. With the
approval of the Federal Reserve Board and the DOJ, the waiting period may be
reduced to no less than fifteen days. The commencement of an antitrust action by
the DOJ would suspend the effectiveness of Federal Reserve Board approval of the
Affiliation unless a court specifically orders otherwise. In reviewing the
Affiliation, the DOJ could analyze the Affiliation's effect on competition
differently than the Federal Reserve Board, and thus it is possible that the DOJ
could reach a different conclusion than the Federal Reserve Board regarding the
Affiliation's competitive effects. Failure of the DOJ to object to the
Affiliation may not prevent the filing of antitrust actions or actions on other
grounds by private persons or state attorneys general.
 
     In general, the Federal Reserve Board and the DOJ will examine the impact
of the Affiliation on competition in various product and geographic markets,
including competition for deposits and loans, especially loans to small and
middle market businesses.
 
     The right of UST to exercise the Option under the Stock Option Agreement
also is subject to the prior approval of the Federal Reserve Board, to the
extent that the exercise of the Option would result in UST owning more than 5%
of the outstanding shares of Walden Common Stock. In considering whether to
approve the exercise by UST of its rights under the Option, including its right
to purchase more than 5% of the outstanding shares of Walden Common Stock, the
Federal Reserve Board would in general apply the same statutory criteria as it
would apply to its consideration of whether to approve the Affiliation. The
Stock Option Agreement also provides that at the request of the holder of the
Option, under certain circumstances, Walden will repurchase the Option (and any
shares acquired pursuant to the option beneficially owned by such holder) for
cash. Such repurchase may be subject to the prior approval of the Federal
Reserve Board. In considering whether to approve such repurchase, the Federal
Reserve Board would be concerned principally with the effect of the repurchase
on the capital adequacy of Walden. For further information on the Stock Option
Agreement, see "CERTAIN TERMS OF THE STOCK OPTION AGREEMENT."
 
     Massachusetts Approval.  The Affiliation is also subject to approval of the
Massachusetts BBI under Sections 2 and 4 of Chapter 167A of the Massachusetts
General Laws. The statute requires that the Massachusetts BBI find that the
Affiliation would not unreasonably affect competition among banking institutions
and that it would promote public convenience and advantage. In making such a
determination, the Massachusetts BBI would consider, but would not be limited
to, a showing of net new benefits including initial capital investments, job
creation plans, consumer and business services and commitments to maintain and
open branch offices within a bank's statutory-delineated local community. In
addition, Section 4 mandates that the Massachusetts BBI cannot approve the
Affiliation until it has received notice from the Massachusetts Housing
Partnership Fund (the "MHPF"), that arrangements satisfactory to the MHPF have
been made for UST to pledge an amount of assets as required under the statute to
be available for call by the MHPF for a period of ten years following the
consummation of the Affiliation for purposes of funding various affordable
housing programs, or other similar arrangements have been accepted by the MHPF.
Under the statute, UST also will be required to maintain, for a period of two
years following the consummation of the Affiliation, the asset base of Walden's
subsidiary banks at a level equal to or greater than the total assets of such
banks on the date of consummation of the Affiliation; provided, however, that
the Massachusetts Commissioner of Banks (the "Massachusetts Commissioner") may
waive such asset retention requirement if, in his judgment, economic conditions
warrant such waiver. UST currently intends to request that the Massachusetts
Commissioner grant such waiver. In addition, the Massachusetts BBI may not
approve any proposed
 
                                       36
<PAGE>   50
 
acquisition or merger if such acquisition or merger would result in a bank
holding company holding or controlling in excess of 28% of the total deposits,
exclusive of foreign deposits, of all state and Federally chartered banks in
Massachusetts and all Massachusetts branches existing by authority of a foreign
country; provided, however, that the Massachusetts Commissioner may waive such
maximum deposit requirement if, in his judgment, economic conditions warrant
such waiver. The parties do not expect that approval of the Affiliation by the
Massachusetts BBI will require that the Massachusetts Commissioner waive such
maximum deposit limitation.
 
     UST and Walden have filed all applications necessary to receive the
requisite approvals of the Federal Reserve Board and the Massachusetts BBI. The
Affiliation will not proceed in the absence of all requisite regulatory
approvals. There can be no assurance that either the Federal Reserve Board or
the Massachusetts BBI will approve the Affiliation. If such approvals are
received, there can be no assurance as to the date of such approvals, that such
approvals will not be conditioned in a manner so as to render inadvisable in the
reasonable judgment of UST the consummation of the Affiliation, or that no
action will be brought challenging such approvals. Other than as described
above, UST and Walden are not aware of any other governmental approvals or
actions that are required prior to the parties' consummation of the Affiliation.
It is presently contemplated that, if any such additional governmental approvals
or actions were required, such approvals or actions would be sought. There can
be no assurance, however, that any such additional approvals or actions could be
obtained or, if obtained, would not be conditioned in a manner so as to render
it inadvisable, in the reasonable judgment of UST, to consummate the
Affiliation.
 
     After the Effective Time, UST expects to merge Walden's bank subsidiaries
with one of the UST bank subsidiaries. Receipt of approvals from the FDIC and
from the Massachusetts Commissioner will be required at that time in order to
consummate the merger of the banks. Such approvals, however, are not required
for the consummation of the Affiliation.
 
CERTAIN FEDERAL INCOME TAX CONSEQUENCES
 
     General.  The following is a summary description of federal income tax
consequences of the Affiliation. This summary is not a complete description of
all possible tax consequences of the Affiliation and, in particular, may not
address federal income tax considerations that may affect the treatment of a
stockholder which, at the Effective Time, already owns some UST Common Stock, is
not a U.S. person, is a tax-exempt entity or an individual who acquired Walden
Common Stock pursuant to an employee stock option or otherwise as compensation,
or exercises some form of control over Walden. In addition, no information is
provided herein with respect to the tax consequences of the Affiliation under
applicable foreign, state or local laws. CONSEQUENTLY, EACH WALDEN STOCKHOLDER
IS ADVISED TO CONSULT A TAX ADVISOR AS TO THE SPECIFIC TAX CONSEQUENCES OF THE
TRANSACTION TO THAT STOCKHOLDER. The following discussion is based on the Code,
as in effect on the date of this Joint Proxy Statement - Prospectus, and there
can be no assurances that future legislation, regulations, administrative
rulings or court decisions will not adversely affect the accuracy of the
statements contained herein. The following discussion gives no consideration of
the particular facts or circumstances of any holder of Walden Common Stock and
assumes that the Walden Common Stock held by each holder thereof is held as a
capital asset.
 
     Effect of the Affiliation.  Neither UST nor Walden has requested or will
receive an advance ruling from the Internal Revenue Service as to the tax
consequences of the Affiliation. Consummation of the Affiliation is conditioned
on the delivery of tax opinions from Bingham, Dana & Gould LLP, counsel to UST,
and from Arthur Andersen LLP, tax advisor to Walden, or from any other tax
advisor to Walden which is acceptable to UST and Walden, substantially to the
effect that, on the basis of facts, representations and assumptions set forth in
such opinions which are consistent with the state of facts existing at the
Effective Time, the Affiliation will be treated for federal income tax purposes
as part of one or more reorganizations within the meaning of Section 368 of the
Code.
 
     If the Affiliation constitutes such a reorganization: (i) no gain or loss
will be recognized by UST, Walden or the Merger Subsidiary as a result of the
Affiliation; (ii) no gain or loss will be recognized by stockholders of Walden
on account of their receipt of UST Common Stock in exchange for their Walden
Common Stock as a
 
                                       37
<PAGE>   51
 
result of the Affiliation; (iii) a holder of Walden Common Stock who receives
cash proceeds for fractional interests in UST Common Stock will be treated as if
the fractional shares were distributed as part of the exchange and then were
redeemed by UST; (iv) the tax consequences of the assumed redemption occurring
in connection with the payment of cash in lieu of fractional shares, and of the
redemption of Walden Common Stock by holders of Walden who perfect their
statutory dissenters' rights, will be determined in accordance with Section 302
of the Code but should generally give rise to capital gain or loss, which
capital gain or loss will be long-term if the Walden Common Stock has been held
for more than one year at the Effective Time; (v) the tax basis of the UST
Common Stock received by stockholders who exchange Walden Common Stock for UST
Common Stock in the Affiliation will be the same as the tax basis of the Walden
Common Stock surrendered in exchange therefor (reduced by any amount allocable
to a fractional share interest for which cash is received); and (vi) the holding
period of the UST Common Stock in the hands of the Walden stockholders will
include the holding period of the Walden Common Stock exchanged therefor.
 
     It is a condition to the consummation of the Affiliation that UST receive
an opinion, dated as of the date of the closing of the Affiliation, from its
counsel, Bingham, Dana & Gould LLP, and that Walden receive an opinion, dated as
of the date of this Joint Proxy Statement-Prospectus and of the date of the
closing of the Affiliation, is of its tax advisor, Arthur Andersen LLP, or other
tax advisor acceptable to UST and Walden, substantially to the effect that,
among other things, each assuming that the Affiliation will be consummated in
accordance with the Affiliation Agreement, the Affiliation constitutes a
reorganization under Section 368 of the Code. If such opinions cannot be
delivered because the Affiliation is not deemed a reorganization under the Code
in the opinion of their respective counsel, the Affiliation may not be
consummated. If, however, the parties waive this condition and the Affiliation
is consummated but not treated as a reorganization within the meaning of Section
368 of the Code, no gain or loss will be recognized by Walden, UST or Merger
Subsidiary, however, exchanges of Walden Common Stock, whether for cash or for
UST Common Stock pursuant to the Affiliation, would be taxable transactions. In
that event, each exchanging holder of Walden Common Stock will recognize capital
gain or loss equal to the difference between such holder's adjusted basis in the
Walden Common Stock exchanged and the amount of cash (if any) plus the fair
market value of UST Common Stock (if any) received by such holder in the
Affiliation.
 
     Backup Withholding.  In order to avoid "backup withholding" of federal
income tax on payments of cash to a holder who exchanges his or her Walden
Common Stock, or a portion of his or her Walden Common Stock, for cash, a holder
must, unless an exception applies under the applicable law and regulations,
provide the payor of such cash with such holder's correct taxpayer
identification number ("TIN") on a Form W-9 and certify under penalties of
perjury that such number is correct and that such holder is not subject to
backup withholding. If the correct TIN and certifications are not provided, a
$50 penalty may be imposed on a holder by the Internal Revenue Service and the
cash payments received by a holder may be subject to backup withholding tax at a
rate of 31%.
 
ACCOUNTING TREATMENT
 
     Consummation of the Affiliation is conditioned upon the Affiliation being
accounted for as a pooling of interests and the receipt by each of UST and
Walden of a letter to such effect from Arthur Andersen LLP. Under the pooling of
interests method of accounting, the recorded amounts of the assets and
liabilities of UST and Walden will be carried forward at their previously
recorded amounts and no goodwill will be created. Revenues and expenses will be
retroactively presented as if UST and Walden were combined for the entire fiscal
period in which the Affiliation occurs and for all periods prior to the
Affiliation at previously recorded amounts.
 
     In order for the Affiliation to qualify for pooling of interests accounting
treatment, substantially all of the outstanding Walden Common Stock must be
exchanged for UST Common Stock with substantially similar terms. UST and Walden
have agreed to use their best efforts to cause the Affiliation to qualify for
pooling of interests accounting treatment, provided that UST is not precluded
from exercising its rights under the Stock Option Agreement. See "THE
AFFILIATION -- Conditions of the Affiliation."
 
     For information concerning certain conditions to be imposed in connection
with the consummation of the Affiliation with respect to the exchange of Walden
Common Stock for UST Common Stock by Affiliates (as defined below) of Walden and
certain restrictions to be imposed on the transferability of the UST Common
 
                                       38
<PAGE>   52
 
Stock to be received by those Affiliates, in order, among other things, to
assure the availability of pooling of interests accounting treatment, see "THE
AFFILIATION -- Resales by Affiliates."
 
EMPLOYEE MATTERS
 
     UST has agreed in the Affiliation Agreement that, with respect to any
employee of Walden or any of its affiliates who is transferred to UST or any
affiliate of UST and who becomes a participant in any employee benefit plan,
program or arrangement maintained or funded by UST or any of its affiliates
(each such employee, a "Transferred Employee"), it will cause the plan, program
or arrangement to treat the service of the Transferred Employee with Walden, or
any of Walden's affiliates, as service rendered to UST or UST's affiliates, as
the case may be, for purposes of eligibility to participate, vesting and
eligibility for special benefits under such plan, program or arrangement, but
not for purposes of benefit accrual. In addition, UST has agreed to provide
Transferred Employees with the types and levels of employee benefits maintained
by UST for similarly situated employees.
 
     UST has also agreed in the Affiliation Agreement that, for a period of one
year following the Closing Date, UST will provide Transferred Employees with a
severance plan with provisions that are at least as favorable in the aggregate
as the severance plan currently maintained by Walden for such employee. Any
employee of Walden or its affiliates who does not become a Transferred Employee
is entitled to severance benefits under the severance plan currently maintained
by Walden for such employee. UST will have no obligation to any Transferred
Employee under Walden's 1993 Employee Stock Purchase Plan or its Deferred
Compensation Plan, each of which will be terminated by Walden prior to the
Effective Time.
 
     In addition, all rights with respect to Walden Common Stock pursuant to
stock options granted by Walden under any stock option plans of Walden and which
are outstanding at the Effective Time shall be converted into corresponding
rights to purchase shares of UST Common Stock. The rights to UST Common Stock to
be received by holders of Walden stock options upon consummation of the
Affiliation will be identical to the rights such optionees had under the Walden
stock option plans which covered such stock options, except that (i) all
references to Walden shall be deemed to be references to UST and (ii) the number
of shares of UST Common Stock subject to such options and the exercise price of
such options will be adjusted to reflect the Conversion Number. The number of
shares of UST Common Stock subject to such stock options will be equal to the
product of the (x) number of shares of Walden Common Stock previously subject
thereto and (y) the Conversion Number, rounded down to the nearest whole share.
The exercise price per share of UST Common Stock shall be equal to (x) the
exercise price per share of Walden Common Stock previously subject thereto
divided by (y) the Conversion Number, rounded up to the nearest cent. UST has
agreed to file a registration statement on Form S-3 or Form S-8, as the case may
be, with respect to the shares of UST Common Stock subject to the Walden stock
options to be assumed by UST. UST will use its reasonable efforts to maintain
the effectiveness of such registration statement for so long as such options
remain outstanding. Under the Affiliation Agreement, after August 30, 1996, no
further stock options may be granted by Walden without the prior consent of UST.
 
     For a description of the effect of the Affiliation on certain other
employee benefits provided by Walden, see "THE AFFILIATION -- Interests of
Certain Persons in the Affiliation."
 
INTERESTS OF CERTAIN PERSONS IN THE AFFILIATION
 
     Certain members of UST's management and the UST Board and Walden's
management and the Walden Board may be deemed to have certain interests in the
Affiliation that are in addition to their interests as stockholders of UST or
Walden, as the case may be. The executive officers and directors of UST and
certain executive officers and directors of Walden will be executive officers
and directors of UST following the Affiliation. See "THE AFFILIATION --
Management and Operations After the Affiliation." UST has agreed (i) to honor
the existing severance arrangements of certain officers and employees of Walden,
(ii) to maintain Walden's directors' and officers' liability insurance for a
period of six years (or substitute a comparable policy), and (iii) to honor,
after the Effective Time to the extent permissible under federal and
Massachusetts law and regulation, the indemnification provisions set forth in
the articles of incorporation and by-laws of Walden and its subsidiaries with
respect to acts or omissions taken prior to the Effective Time. See "THE
AFFILIATION -- Indemnification and Insurance." In the Affiliation Agreement, UST
and Walden
 
                                       39
<PAGE>   53
 
have agreed to terminate, as of the Effective Time, the existing severance
agreements between Walden and each of Ms. Bergemann and Messrs. Bradbury,
Cushing and Gilles and that, subject to the terms thereof, each will be entitled
to the payment and benefits provided for therein. In addition, it is expected
that the existing severance agreement between Walden and Mr. Olson may be
terminated at or near the Effective Time and that, subject to the terms thereof,
he will be entitled to payment and benefits provided for therein. The amounts of
the severance payments currently expected to be received by the foregoing
persons as a result of the Affiliation under the terms of their severance
agreements are approximately $408,600, $2,593,999, $1,307,046, $735,135 and
$704,535, respectively. Payments under such severance agreements will be made by
Walden no later than the Effective Time.
 
     Directors, officers and employees with stock options outstanding at the
Effective Time under stock option plans of Walden will be entitled to have their
options converted into options with respect to UST Common Stock. See "THE
AFFILIATION -- Employee Matters." Based on the price of Walden Common Stock
immediately before the execution and announcement of the Affiliation Agreement
($20.50 on August 29, 1996), and the recent price of UST Common Stock ($17.69 on
November 4, 1996), it is estimated that the aggregate increase in the total
value (market price less exercise price of all option shares) of the Walden
stock options held by each director or executive officer of Walden, excluding
the value of all such options immediately before the execution of the
Affiliation Agreement, but including the value of all such options that vested
or will vest in connection with the Affiliation, is approximately as follows:
Mr. Atkins, $39,713; Mr. Bradbury, $1,287,161; Mr. Cutler, $0; Mr. Doody, $0;
Mr. Ehrenfried, $39,713; Mr. Griffith, $39,713; Mr. Lombard, $39,713; Mr. Tod,
$0; Ms. Bergemann, $439,588; Mr. Cushing, $738,422; Mr. Gilles, $665,184; and
Mr. Olson, $325,392.
 
INDEMNIFICATION AND INSURANCE
 
     Under the Affiliation Agreement, after the Effective Time, UST has agreed
to honor the indemnification provisions for officers and directors currently set
forth in the Walden Articles or By-laws or the articles of association, charter
or by-laws of any of Walden's subsidiaries with respect to acts and omissions
taken by such officers and directors prior to the Effective Time, but only to
the extent permitted by federal and Massachusetts law and regulation.
 
     UST has also agreed, pursuant to the Affiliation Agreement, to maintain
Walden's (including its subsidiaries') existing directors' and officers'
liability insurance covering persons who are currently covered by Walden's
insurance policies for a period of six years after the Effective Time on terms
no less favorable than those in effect on August 30, 1996. Walden has agreed
that UST may substitute policies providing at least comparable coverage and
containing terms and conditions no less favorable than those in effect on August
30, 1996.
 
RIGHTS OF DISSENTING STOCKHOLDERS
 
     If the Affiliation becomes effective, a stockholder of Walden who does not
vote in favor of the Affiliation and who follows the procedures prescribed under
Massachusetts law may require Walden (as it exists after the Effective Time) to
pay the fair value, determined as provided under applicable statute, for the
Dissenting Shares held by such stockholder. The following is a summary of
certain features of the relevant Massachusetts law, the provisions of which are
set forth in full in Appendix F annexed hereto. IN ORDER TO EXERCISE SUCH
STATUTORY APPRAISAL RIGHTS, STRICT ADHERENCE TO THE STATUTORY PROVISIONS IS
REQUIRED, AND EACH STOCKHOLDER WHO MAY DESIRE TO EXERCISE SUCH RIGHTS SHOULD
CAREFULLY REVIEW AND ADHERE TO SUCH PROVISIONS.
 
     A dissenting stockholder of Walden who desires to pursue the appraisal
rights available must adhere to the following procedures: (1) file a written
objection to the Affiliation with Walden before the taking of the stockholders'
vote on the Affiliation, stating the intention of such stockholder to demand
payment for shares owned by such stockholder if the Affiliation is approved and
consummated; (2) refrain from voting shares owned by such stockholder in favor
of the Affiliation; and (3) within twenty days of the date of mailing of a
notice by Walden (as its exists after the Effective Time) to objecting
stockholders that the Affiliation has become effective, make written demand to
Walden (as it exists after the Effective Time) for payment for said
stockholder's shares. Such written objection should be delivered to Walden, 125
Nagog Park, Acton,
 
                                       40
<PAGE>   54
 
Massachusetts 01720, Attn.: Josiah S. Cushing, II, Clerk, and such written
demand should be delivered to Walden (as it exists after the Effective Time),
c/o UST, 40 Court Street, Boston, Massachusetts 02108, Attn.: Eric R. Fischer,
Executive Vice President, General Counsel and Clerk. It is recommended that such
objection and such demand be sent by registered or certified mail, return
receipt requested.
 
     A dissenting stockholder, who files the required written objection with
Walden prior to the stockholder vote, need not vote against the Affiliation, but
a vote in favor of the Affiliation will constitute a waiver of such
stockholder's statutory appraisal rights. Stockholders should note that
returning a properly signed proxy card that does not indicate a vote or an
abstention on approval of the Affiliation Agreement will constitute a vote in
favor of the Affiliation Agreement. A vote against the Affiliation does not,
alone, constitute a written objection. Pursuant to the applicable statutory
provisions, notice that the Affiliation has become effective will be sent to
each objecting stockholder of Walden within ten days after the date on which the
Affiliation becomes effective.
 
     The value of the Walden Common Stock will be determined initially by Walden
(as it exists after the Effective Time) and the dissenting stockholder. If,
during the period of thirty days after the expiration of the period during which
the foregoing demand for payment may be made, Walden (as it exists after the
Effective Time) and the stockholder fail to agree on an appraisal value, either
of them may file a bill in equity in the Superior Court of Middlesex County,
Massachusetts, asking that the court determine the matter in issue. The bill in
equity must be filed within four months after the date of expiration of the
foregoing thirty-day period. After a hearing, the court shall enter a decree
determining the fair value of the Walden Common Stock and shall order Walden (as
it exists after the Effective Time) to make payment of such value, with
interest, if any, to the stockholders entitled to said payment, upon transfer by
them to Walden (as it exists after the Effective Time) of the certificate or
certificates representing the Walden Common Stock held by said stockholders.
 
     For appraisal proceeding purposes, value is determined as of the day before
the approval of the Affiliation by stockholders, excluding any element of value
arising from the expectation or accomplishment of the Affiliation.
 
     Under Massachusetts statutory law, procedures relating to dissenters'
rights are stated to be the exclusive remedy available to a stockholder
objecting to the Affiliation, except where the objection is based on the
contention that the Affiliation will be or is illegal or fraudulent as to said
stockholder. However, under Massachusetts case law, dissenting stockholders may
not be limited to the statutory remedy of judicial appraisal where violations of
fiduciary duty are found.
 
     The law pertaining to the statutory appraisal remedy also contains
provisions regarding costs, dividends on dissenting shares, rights under
dissenting shares prior to purchase, discontinuance of dissenters' rights, and
certain miscellaneous matters. See Appendix F.
 
NASDAQ LISTING
 
     The Affiliation Agreement provides for the filing of, and UST has filed or
will file, a listing application with NASDAQ covering the shares of UST Common
Stock issuable pursuant to the Affiliation. The obligation of Walden to effect
the Affiliation is subject to the condition that such shares of UST Common Stock
be authorized for listing on NASDAQ effective upon official notice of issuance.
 
RESALES BY AFFILIATES
 
     Shares of UST Common Stock to be issued to stockholders of Walden in
connection with the Affiliation will have been registered with the Commission
under the Securities Act. Thus, all shares of UST Common Stock to be received by
holders of Walden Common Stock upon consummation of the Affiliation will be
freely transferable by those stockholders of Walden not deemed to be
"Affiliates" of UST or Walden. Under the Securities Act, "Affiliates" generally
are defined as persons (often considered to include, but not necessarily limited
to, executive officers, directors and ten-percent stockholders) who control, are
controlled by, or are under common control with (i) UST or Walden at the time of
the Walden Meeting or (ii) UST at or after the Effective Time.
 
     Rule 145 promulgated by the Commission under the Securities Act restricts
the sale of UST Common Stock received in the Affiliation by former Affiliates of
Walden and certain of their family members and related interests. Generally
speaking, during the two years following the Effective Time, Affiliates of
Walden,
 
                                       41
<PAGE>   55
 
may publicly resell the UST Common Stock received by them in the Affiliation
provided that such sales comply with Rule 145 limitations as to the amount of
UST Common Stock sold in any three-month period and as to the manner of sale.
After the two-year period, such former Affiliates of Walden who are not
Affiliates of UST may resell their shares without any restriction. Persons who
are affiliates of UST prior to the Effective Time generally will remain subject
to limitations and restrictions under Commission Rule 144 with respect to shares
they may receive in connection with the affiliation (and any other shares of UST
Common Stock they may own), so long as they continue to be Affiliates. The
ability of Affiliates to resell shares of UST Common Stock received in the
Affiliation under Rule 145 as summarized herein will be subject to UST's having
satisfied its Exchange Act reporting requirements for specified periods prior to
the time of sale.
 
     Affiliates of Walden also will be permitted to resell UST Common Stock
received in the Affiliation without any restrictions provided that such sales
are made pursuant to an effective registration statement filed with the
Commission under the Securities Act or by means of another available exemption
from the Securities Act registration requirements. This Joint Proxy Statement -
Prospectus may not be used to effectuate any resales of UST Common Stock
received by persons who may be deemed to be Affiliates of UST or Walden.
 
     UST and Walden have agreed to use all reasonable efforts to cause each
person who may be deemed to be an Affiliate (which term shall mean any person so
defined for purposes of qualifying the Affiliation for pooling of interests
accounting treatment under the Commission's Accounting Series Releases 130 and
135, and which term shall also mean when used with respect to Walden, any person
so defined in accordance with Rule 145) of such party to execute and deliver to
the other party, a letter, in the case of UST Affiliates, substantially in the
form attached to the Affiliation Agreement as Exhibit B-1 (the "UST Affiliates
Letter"), and in the case of Walden, substantially in the form attached to the
Affiliation Agreement as Exhibit B-2 (the "Walden Affiliates Letter", and
generally, an "Affiliates Letter").
 
     Commission guidelines with respect to the qualification of the Affiliation
for pooling of interests accounting treatment limit sales of shares of the
acquiring and acquired company by Affiliates of either company in a business
combination. Commission guidelines indicate further that the pooling of
interests method of accounting generally will not be challenged on the basis of
sales by Affiliates of the acquiring or acquired company if they do not dispose
of any of the shares of the corporation they own or shares of a corporation they
receive in connection with a merger during the period beginning thirty days
before the merger and ending when financial results ("Post-Merger Financial
Results") covering at least thirty days of post-merger operations of the
combined entity have been published. In the UST Affiliates Letter, Affiliates of
UST have agreed not to sell, transfer or otherwise dispose of, or reduce the
risk of ownership with respect to shares of UST Common Stock acquired in the
Affiliation in violation of these guidelines. In the Walden Affiliates Letter,
Affiliates of Walden have agreed not to sell, transfer or otherwise dispose of,
or reduce the risk of ownership with respect to any shares Walden Common Stock
held by the Affiliate, or any shares of UST Common Stock in violation of these
guidelines.
 
     The Walden Affiliates Letter further provides that an Affiliate of Walden
will not sell, assign, transfer, or otherwise dispose of any shares of UST
Common Stock obtained as a result of the Affiliation, except in compliance with
the Securities Act and the rules and regulations of the Commission thereunder.
Walden certificates surrendered for exchange by any person who is an Affiliate
of Walden for purposes of Rule 145(c) will not be exchanged for certificates
representing shares of UST Common Stock until UST has received an executed
Affiliates Letter from such person. Prior to publication of Post-Merger
Financial Results, UST will not transfer on its books any shares of UST Common
Stock received by an Affiliate pursuant to the Affiliation. The stock
certificates representing UST Common Stock issued to Affiliates of Walden in the
Affiliation will bear a legend summarizing the applicable Rule 145 restrictions.
 
     UST has agreed in the Affiliation Agreement to publish not later than
thirty days following the end of the first month after the Effective Time in
which there are at least thirty days of post-Affiliation combined operations,
Post-Merger Financial Results as contemplated by and in accordance with the
terms of the Commission's Accounting Series Release No. 135.
 
CONVERSION OF SHARES; EXCHANGE OF CERTIFICATES
 
     Conversion of Shares of Walden Common Stock.  By virtue of the Affiliation,
automatically and without any action on the part of any holder thereof: (a) each
then-outstanding share of Walden Common Stock not
 
                                       42
<PAGE>   56
 
owned by UST directly or indirectly (except for any such shares of Walden Common
Stock held by UST in a fiduciary capacity), and other than those shares of
Walden Common Stock held in the treasury of Walden and Dissenting Shares, will
be converted into 1.9 shares of UST Common Stock and each holder will also
receive a corresponding amount of preferred stock purchase rights associated
therewith pursuant to the UST Rights Agreement (See "THE AFFILIATION -- Terms of
the Affiliation" and "DESCRIPTION OF UST CAPITAL STOCK -- Stockholder Rights
Agreement"); (b) each then-outstanding share of Walden Common Stock owned by UST
or any subsidiary of UST (except for any such shares of Walden Common Stock held
by UST or its subsidiaries in a fiduciary capacity) will be cancelled, retired
and cease to exist; and (c) each share of Walden Common Stock issued and held in
Walden's treasury will be cancelled and retired. No conversion or payment will
be made with respect to the cancellation of shares referred to in clauses (b)
and (c) above. For a discussion of the treatment of Dissenting Shares, see "THE
AFFILIATION -- Rights of Dissenting Stockholders." Under certain circumstances,
UST may choose to adjust the Conversion Number to be greater than 1.9 in order
to prevent the termination of the Affiliation Agreement by Walden. See "THE
AFFILIATION -- Termination of the Affiliation Agreement."
 
     The Conversion Number is the product of arm's length negotiations between
the respective managements of UST and Walden. In determining the fairness of the
Conversion Number, the management of UST had the benefit of advice from its
financial advisor, the investment banking firm of Fox-Pitt, Kelton, and the
management of Walden had the benefit of advice from its financial advisor, the
investment banking firm of PaineWebber. See "THE AFFILIATION -- Opinion of
Financial Advisor to UST" and "-- Opinion of Financial Advisor to Walden."
Because the Conversion Number is fixed and the market price of UST Common Stock
is subject to fluctuation, the value of the shares of UST Common Stock that
holders of Walden Common Stock will receive in the Affiliation may increase or
decrease prior to and following the Affiliation.
 
     Manner of Exchanging Walden Certificates for UST Certificates.  UST has
appointed UST's wholly-owned subsidiary, USTC (the "Exchange Agent"), to effect
the exchange of certificates in connection with the Affiliation. Promptly after
the Effective Time, UST will send to each holder of record (other than UST or
its subsidiaries for shares of Walden Common Stock it holds other than in a
fiduciary capacity and holders of shares of Walden Common Stock who have
perfected their rights of appraisal) of a Walden certificate which immediately
prior to the Effective Time represented outstanding shares of Walden Common
Stock (a "Walden Certificate"), a letter of transmittal and instructions for its
use in effecting such surrender of the Walden Certificates in exchange for
certificates representing shares of UST Common Stock. Upon surrender of a Walden
Certificate for exchange and cancellation to the Exchange Agent, together with a
duly executed letter of transmittal and any other required documents, the holder
of such Walden Certificate will be entitled to receive, in exchange therefor, a
certificate representing the number of shares of UST Common Stock to which such
Walden Certificate holder is entitled upon consummation of the Affiliation and a
check representing cash in lieu of any fractional share thereof, and the Walden
Certificate so surrendered will forthwith be cancelled.
 
     WALDEN CERTIFICATES SHOULD NOT BE RETURNED WITH THE ENCLOSED PROXY AND
SHOULD NOT BE FORWARDED TO THE EXCHANGE AGENT UNTIL THE WALDEN STOCKHOLDER HAS
RECEIVED A TRANSMITTAL LETTER.
 
     If any certificate for shares of UST Common Stock or a check representing
cash in lieu of any fractional share thereof is to be issued in a name other
than that in which a Walden Certificate surrendered for exchange is registered,
the Walden Certificate so surrendered shall be properly endorsed (or accompanied
by an appropriate instrument of transfer) and otherwise in proper form for
transfer, and the person requesting such exchange shall pay to the Exchange
Agent in advance any transfer or other taxes by reason of the issuance of a
certificate representing shares of UST Common Stock in any name other than that
of the registered holder of the Walden Certificate surrendered, or which are
required for any other reason, or shall establish to the satisfaction of the
Exchange Agent that such tax has been paid or is not payable.
 
     Lost Certificates.  In the event that any Walden Certificate is lost,
stolen or destroyed, upon receipt by UST of appropriate evidence as to such
loss, theft or destruction and as to the ownership of the Walden
 
                                       43
<PAGE>   57
 
Certificate, and the receipt by UST of appropriate and customary
indemnification, UST will issue shares of UST Common Stock and the fractional
share payment, if any, in exchange for the lost, stolen or destroyed Walden
Certificate.
 
     Distributions with Respect to Unexchanged Walden Certificates.  No dividend
or other distribution payable after the Effective Time on UST Common Stock will
be paid to the holder of any Walden Certificates until such holder physically
surrenders such Walden Certificates for exchange as instructed. Subject to any
applicable law, upon surrender of any Walden Certificate, such holder will
receive (a) a certificate representing the shares of UST Common Stock into which
the former shares of Walden Common Stock represented by such certificate have
been converted, (b) any withheld dividends or other distributions (without
interest) and (c) any withheld cash payments (without interest) for any
fractional share to which such stockholder is entitled.
 
     Post Effective Time.  After the Effective Time, there will be no transfers
on the transfer books of Walden of the shares of Walden Common Stock which were
outstanding immediately at the Effective Time. If, after the Effective Time,
Walden Certificates representing such shares are presented for transfer to
Walden, they will be cancelled and exchanged for certificates representing
shares of UST Common Stock pursuant to the terms of the Plan of Merger. After
the Effective Time, holders of Walden Certificates (or certificates of its
corporate predecessors in interest, including Concord or Braintree, which have
been converted into Walden Certificates) will cease to be and have no rights as
stockholders of such entities except to receive shares of UST Common Stock or
cash in lieu of fractional shares of Walden Common Stock converted or rights
afforded dissenting stockholders.
 
CONDITIONS TO THE CONSUMMATION OF THE AFFILIATION
 
     Conditions to Each Party's Obligations.  The respective obligations of each
of UST and Walden to effect the Affiliation are subject to the fulfillment of
the following conditions, none of which may be waived by the parties:
 
          (a) the Affiliation Agreement, the Plan of Merger and each of the
     transactions contemplated thereby shall have been approved by the
     respective requisite affirmative votes of the holders of UST Common Stock
     and Walden Common Stock entitled to vote thereon;
 
          (b) all authorizations, consents, orders or approvals of, or
     declarations or filings with, and all expirations of waiting periods
     imposed by, any governmental or regulatory authority or agency which are
     necessary for the consummation of the Affiliation, shall have been filed,
     occurred or been obtained other than consents, the failure of which to
     obtain would neither make it impossible to consummate the Affiliation nor
     result in a Material Adverse Effect on UST after the Affiliation (all such
     authorizations, orders, declaration, approvals, filings and consents and
     the lapse of all such waiting periods being referred to as the "Requisite
     Regulatory Approvals") and all such Requisite Regulatory Approvals shall be
     in full force and effect;
 
          (c) the Registration Statement shall have become effective under the
     Securities Act and shall not be subject to a stop order or a threatened
     stop order; and
 
          (d) no temporary restraining order, preliminary or permanent
     injunction or other order issued by any court of competent jurisdiction or
     other legal restraint or prohibition preventing the consummation of the
     Affiliation shall be in effect;
 
          (e) UST and Walden shall have each received a letter from Arthur
     Andersen LLP, addressed to each of them, to the effect that the Affiliation
     will qualify for pooling of interest accounting treatment.
 
     Conditions to UST's Obligations.  The obligation of UST to effect the
Affiliation also is subject to the satisfaction of additional conditions,
including, but not limited to, the following conditions, any of which may be
waived by UST:
 
          (a) there shall not have been any change in the business, assets,
     financial condition or results of operations of Walden or any of its
     subsidiaries which has had, or is reasonably likely to have, individually
 
                                       44
<PAGE>   58
 
     or in the aggregate, a Material Adverse Effect (as defined in the
     Affiliation Agreement) on Walden as a whole or any of its banking
     subsidiaries taken on an individual basis;
 
          (b) the obligations of Walden under the Affiliation Agreement shall
     have been duly performed or complied with in all material respects, and the
     representations and warranties of Walden contained in the Affiliation
     Agreement shall be true and correct in all material respects as of the date
     of the Affiliation Agreement and as of the Effective Time as though made at
     and as of the Effective Time (except as otherwise specifically contemplated
     by the Affiliation Agreement according to the standard set forth therein
     and except with respect to any representation or warranty which
     specifically relates to an earlier date and UST shall have received a
     certificate to that effect from the chairman or president and the chief
     financial officer or chief accounting officer of Walden;
 
          (c) all permits, consents, waivers, clearances, approvals and
     authorizations of all non-governmental and non-regulatory third parties
     necessary in connection with the consummation of the Affiliation and
     required to be received by Walden have been received, other than those the
     failure of which to obtain would neither make it impossible to consummate
     the Affiliation nor result in a Material Adverse Effect with respect to UST
     (on a consolidated basis with Walden);
 
          (d) Bingham, Dana & Gould LLP shall have delivered to UST a tax
     opinion, dated as of the date of the closing of the Affiliation
     substantially to the effect that, on the basis of facts, representations
     and assumptions set forth in such opinion, the Affiliation will be treated
     for federal income tax purposes as a reorganization within the meaning of
     Section 368 of the Code and addressing such other opinions relating to
     federal income tax effects as UST may reasonably require which are
     customary in such transactions;
 
          (e) Walden shall have delivered to UST, Walden Affiliates Letters
     executed by each of the Affiliates of Walden;
 
          (f) Walden shall have terminated its 1993 Employee Stock Purchase Plan
     and its Deferred Compensation Plan; and
 
          (g) there shall not have been any action taken by any federal or state
     governmental agency or authority which, in connection with the granting of
     any consent or Requisite Regulatory Approval necessary to consummate the
     Affiliation or otherwise, imposes any condition or restriction upon UST or
     any of its subsidiaries, or Walden, after the Affiliation (including,
     without limitation, requirements relating to the disposition of assets or
     limitations on interest rates) which would so materially adversely impact
     the economic or business benefits of the transactions contemplated by the
     Affiliation Agreement, as to render inadvisable in the reasonable judgment
     of UST the consummation of the Affiliation.
 
     Conditions to Walden's Obligations.  The obligations of Walden to effect
the Affiliation also are subject to the satisfaction of certain additional
conditions, including, but not limited to, the following conditions, any of
which may be waived by Walden:
 
          (a) there shall not have been any change in the business, assets,
     financial condition, results of operations of UST or any of its
     subsidiaries, which has had, or is likely to have, individually or in the
     aggregate, a Material Adverse Effect on UST as a whole or any of its
     banking subsidiaries on an individual basis;
 
          (b) the obligations of UST under the Affiliation Agreement shall have
     been duly performed or complied with in all material respects and the
     representations and warranties of UST contained in the Affiliation
     Agreement shall be true and correct in all material respects, as of the
     date of the Affiliation Agreement and as of the Effective Time as though
     made at and as of the Effective Time, except as otherwise specifically
     contemplated by the Affiliation Agreement according to the standard set
     forth in the Affiliation Agreement or any representation or warranty which
     specifically relates to an earlier date, and Walden shall have received a
     certificate to that effect from the chairman or president and chief
     financial officer or chief accounting officer of UST;
 
          (c) all permits, consents, waivers, clearances, approvals and
     authorizations of all non-governmental and non-regulatory third parties
     necessary in connection with the consummation of the Affiliation that are
 
                                       45
<PAGE>   59
 
     required to be received by UST have been received, other than those the
     failure of which to obtain would neither make it impossible to consummate
     the Affiliation nor result in a Material Adverse Effect with respect to UST
     (on a consolidated basis with Walden) after the Affiliation;
 
          (d) Arthur Andersen LLP, or another tax advisor of Walden acceptable
     to Buyer and Seller, shall have delivered to Walden a tax opinion dated as
     of this Joint Proxy Statement -- Prospectus and as of the date of the
     closing of the Affiliation, each substantially to the effect that, on the
     basis of facts, representations and assumptions set forth in such opinion,
     the Affiliation will be treated for federal income tax purposes as a
     reorganization within the meaning of Section 368 of the Code and no gain or
     loss will be recognized by the stockholders of Walden upon the receipt,
     pursuant to the Affiliation Agreement, of UST Common Stock in exchange for
     Walden Common Stock (such opinion will not extend to cash received in lieu
     of fractional share interests or cash received by dissenting stockholders,
     if any) and addressing such other opinions relating to federal income tax
     effects as Walden may reasonably require which are customary in such
     transactions;
 
          (e) UST shall have delivered to Walden, UST Affiliates Letters
     executed by each of the Affiliates of UST;
 
          (f) the shares of UST Common Stock issuable to Walden stockholders
     pursuant to the Affiliation Agreement and the Plan of Merger shall have
     been authorized for listing on NASDAQ upon official notice of issuance; and
 
          (g) the Exchange Agent shall have delivered a certificate to Walden to
     the effect that UST (i) has given the Exchange Agent instructions and
     authorization to issue a sufficient number of shares of UST Common Stock in
     exchange for all outstanding shares of Walden Common Stock and (ii) has
     deposited sufficient funds with the Exchange Agent to pay a reasonable
     estimate of the cash payments necessary to pay for fractional share
     interests.
 
CONDUCT OF BUSINESS PENDING THE AFFILIATION
 
     Pursuant to the Affiliation Agreement, Walden has agreed that, until the
earlier of the Effective Time or the termination of the Affiliation Agreement,
Walden:
 
          (a) shall, and shall cause each of its subsidiaries to, conduct its
     business and engage in transactions only in the ordinary and usual course
     of business consistent with past practices, which shall mean (i) conducting
     its banking and other business in the ordinary and usual course, (ii)
     refraining from any of the activities described in (b) below, (iii) not
     entering into any material transactions except in the ordinary and usual
     course of business consistent with past practices and (iv) complying with
     the following covenants:
 
             (A) maintaining its corporate existence and good standing, except
        where any failure to maintain such good standing does not or would not
        have a Material Adverse Effect on Walden or any of its Significant
        Subsidiaries (for purposes of this Joint Proxy Statement - Prospectus,
        the term "Significant Subsidiary" means with respect to Walden, any
        "Significant Subsidiary" as defined in Commission Regulation S-X and,
        specifically, whether or not so defined in such Regulation, Walden
        Financial Corporation, Builders Collaborative, Inc., Walden Securities
        Corporation, Inc., Braintree Savings Corporation, Bra-Prop Corporation
        and Braintree Securities Corporation);
 
             (B) using all reasonable efforts to maintain and keep its
        properties in as good repair and condition in all material respects as
        they presently exist, except for ordinary wear and tear and damage due
        to casualty;
 
             (C) using all reasonable efforts to maintain in full force and
        effect insurance generally comparable in amount and in scope of coverage
        to that now maintained by it;
 
             (D) complying with and performing in all material respects its
        obligations and duties (y) under contracts, leases and documents
        relating to or affecting its assets, properties and business and (z)
        imposed upon it by all federal, state and local laws and all rules,
        regulations and orders imposed by
 
                                       46
<PAGE>   60
 
        federal, state or local governmental authorities, judicial orders,
        judgments, decrees and similar determinations; and
 
             (E) using all reasonable efforts to preserve its business
        organization intact and the goodwill of those having business
        relationships with Walden or any of its subsidiaries, to keep available
        the services of its officers and employees as a group and to maintain
        satisfactory relationships with borrowers, depositors, other customers
        and others having business relationships with it;
 
          (b) shall not, and shall not permit any of its subsidiaries to,
     without the prior written consent of UST (i) engage in any material
     transaction or incur or sustain any material obligation or liability except
     in the ordinary, regular and usual course of business consistent with past
     practices, (ii) offer an interest rate on any deposit such that such
     deposit would be deemed a "brokered deposit," (iii) except in the ordinary
     course of business (except for (A) certain sales of automobiles and (B)
     loan and securities acquisitions and dispositions in the ordinary course of
     business consistent with past practices, in each case as more fully set
     forth in the Affiliation Agreement), sell, lease, encumber or otherwise
     dispose of any assets, (iv) file any application or give any notice to
     customers or governmental authorities or agencies to open, close or
     relocate any branch or open, close, relocate or terminate the operations of
     any branch, or (v) waive any material right it has with respect to any
     asset except in the ordinary, regular and usual course of business
     consistent with past practice;
 
          (c) shall cooperate with UST with respect to the preparation for the
     combination and integration as of the Effective Time of the businesses,
     systems and operations of Walden and UST;
 
          (d) shall not pay or declare any dividends or make other distributions
     in respect of the Walden Common Stock except for regular quarterly cash
     dividends at a rate not in excess of Walden's current dividend rate and
     subject to certain other provisions of the Affiliation Agreement;
 
          (e) shall not adopt or amend in any material respect any pension,
     benefit or other plans or enter into any employment, retention, severance
     or similar contracts or amend such contracts or plans to increase the
     amount payable or benefits provided thereunder, or pay any bonuses to it or
     its subsidiaries' employees except as provided for in the Affiliation
     Agreement and in the ordinary course of business consistent with past
     practices;
 
          (f) except as set forth in the Affiliation Agreement, shall not with
     respect to itself and its subsidiaries, authorize, recommend, propose or
     enter into an agreement with respect to any merger, consolidation, purchase
     and assumption transaction or business combination (other than the
     Affiliation), any acquisition of a material amount of assets or securities
     or assumption of liabilities, any disposition of a material amount of
     assets or securities, or any release or relinquishment of any material
     contract rights;
 
          (g) shall not propose or adopt amendments to it or its subsidiaries'
     charter or other incorporation documents or by-laws;
 
          (h) shall not, and shall not permit its subsidiaries to, issue,
     deliver or sell shares of its or their capital stock or securities
     convertible into its or their capital stock (other than (i) the sale of a
     certain amount of shares of Walden Common Stock pursuant to options or
     rights issued pursuant to Walden's 1993 Employee Stock Purchase Plan as
     more fully set forth in the Affiliation Agreement, (ii) pursuant to
     employee benefit plans or arrangements, dividend reinvestment plans or the
     terms of convertible securities outstanding as of the date of the
     Affiliation Agreement), and (iii) except pursuant to the Option), or effect
     any stock split, reclassification or similar transaction or otherwise
     change its capitalization as it existed on June 30, 1996;
 
          (i) shall not grant any options or rights to acquire any of its
     capital stock not existing on August 30, 1996;
 
          (j) shall not, and shall not permit its subsidiaries to, purchase,
     redeem or otherwise acquire any shares of its capital stock or any
     securities convertible into or exercisable for shares of its capital stock,
     except in a fiduciary capacity;
 
          (k) shall not impose or permit to exist any material lien, charge or
     encumbrance on any capital stock held by it or any of its subsidiaries;
 
                                       47
<PAGE>   61
 
          (l) shall not, and shall not permit its subsidiaries to, incur any
     debt obligations or obligations for borrowed money, or to guarantee the
     same, other than in the ordinary course of business consistent with past
     practices;
 
          (m) shall not incur or commit to any capital expenditures or any
     obligations or liabilities in connection therewith, other than in the
     ordinary and usual course of business consistent with past practices and,
     in all cases, shall consult with UST with respect to capital expenditures
     that individually exceed $75,000 or cumulatively exceed $300,000;
 
          (n) shall use all reasonable efforts to improve its business, results
     of operations, financial condition and prospects;
 
          (o) shall not, except as expressly contemplated by the Affiliation
     Agreement, enter into any contract with any Affiliate;
 
          (p) shall not, except for transactions in the ordinary course of
     business consistent with past practices, enter into, terminate, renew or
     amend any material contract or alter any material leases or contracts,
     except as provided in the Affiliation Agreement;
 
          (q) shall not, except in the ordinary course of business and
     consistent with past practice, materially change its investment securities
     portfolio or its "gap position" without prior consultation with UST; and
 
          (r) shall not agree, in writing or otherwise, to take any of the
     foregoing actions or any action which would make any of its representations
     or warranties made in the Affiliation Agreement untrue or incorrect in any
     material respect.
 
     Walden has agreed to use all reasonable efforts to renew or extend on a
month-to-month basis or for such term as requested by UST, any lease of a branch
office of any subsidiary, other lease of real property or lease relating to
furniture, fixtures or equipment that is currently in effect but would otherwise
expire on or prior to the Effective Time. Walden has further agreed not to
cancel, terminate or take any other action this is likely to result in any
cancellation or termination of any such lease without prior written notice to
UST. With respect to certain parcels of its real property, Walden has agreed to
cause certain environmental testing and, to the extent requested in writing by
UST, certain environmental contamination remediation to be conducted.
 
     In addition to the above, Walden has specifically agreed that it will not
and its subsidiaries will not, directly or indirectly, solicit, encourage,
initiate or participate in any discussion or negotiations with (subject to the
fiduciary obligations of the Walden Board as determined in good faith in
consultation with outside counsel), or provide any information to, any
corporation, partnership, person or other entity (other than UST and its
affiliates) concerning any merger, tender offer, sale of substantial assets
(other than as permitted under the Affiliation Agreement), or sales of stock or
securities involving Walden or its subsidiaries (an "Other Acquisition
Transaction"). In the exercise of the Walden Board's fiduciary obligations,
Walden may participate in discussions with respect to an Other Acquisition
Transaction provided that Walden does not solicit or initiate such discussions.
Notwithstanding the foregoing, Walden is not prohibited from taking and
disclosing to stockholders a position with respect to a tender offer by a third
party pursuant to Rules 14d-9 and 14e-2(a) promulgated under the Exchange Act or
from making such disclosure to stockholders which may be required under
applicable law. Walden has agreed to immediately communicate to UST the identity
of the parties and terms of any proposal, discussion or inquiry relating to a
possible Other Acquisition Transaction.
 
     UST and Walden have agreed to cooperate and use all reasonable efforts to
prepare all necessary documentation and file all applications, notices,
petitions and filings, and to obtain and to cooperate in obtaining permits,
consents, approvals and authorizations of all third parties and governmental
entities necessary or advisable to consummate the transactions contemplated by
the Affiliation Agreement and to comply with the terms and conditions of all
such permits, consents, approvals and authorizations.
 
     UST and Walden have further agreed (i) not to change their respective
methods of accounting, as in effect at December 31, 1995, except as allowed in
the Affiliation Agreement; (ii) to advise the other promptly of any change or
event having a Material Adverse Effect (as defined in the Affiliation Agreement)
on it or its subsidiaries that it believes would or would be reasonably likely
to cause or constitute a material breach of any
 
                                       48
<PAGE>   62
 
of its representations, warranties or covenants contained in the Affiliation
Agreement; and (iii) to coordinate with each other the declaration of any
dividends in respect of UST Common Stock and Walden Common Stock and the record
dates and payment dates relating thereto, it being their intention that holders
of UST Common Stock or Walden Common Stock will not receive two dividends, or
fail to receive one dividend, for any single calendar quarter with respect to
their shares of UST Common Stock and/or Walden Common Stock and any shares of
UST Common Stock any such holder receives pursuant to the Affiliation.
 
     UST has also agreed to cause the shares of UST Common Stock to be issued in
the Affiliation to be approved for listing on the NASDAQ, subject to official
notice of issuance as of or prior to the Effective Time.
 
     From the date of the Affiliation Agreement until the earlier of the
Effective Time or the date of termination of the Affiliation Agreement, UST has
agreed that it will take no action which would (a) materially adversely affect
the ability of any party to obtain any governmental or regulatory consents
required for consummation of the transactions contemplated by the Affiliation
Agreement without the imposition of a burdensome condition or restriction, (b)
materially adversely affect the ability of any party to perform its covenants
and agreements under the Affiliation Agreement, or (c) result in UST entering
into an agreement with respect to an acquisition proposal with a third party
which would result in the Affiliation not being consummated.
 
WAIVER AND AMENDMENT
 
     Waiver.  UST and Walden, with the authorization of their respective Boards
of Directors, may, by written notice to the other party (a) extend the time for
the performance of any of the obligations or other acts required of the other
party contained in the Affiliation Agreement, (b) waive any inaccuracies in the
representations and warranties of the other party contained in the Affiliation
Agreement or in any document delivered pursuant to the Affiliation Agreement, or
(c) waive compliance by the other party of any of its agreements or obligations
under certain sections of the Affiliation Agreement; provided that any extension
or waiver which reduces the amount or changes the form of the consideration to
be delivered to Walden stockholders may not be made after Walden stockholders
have approved the Affiliation Agreement unless stockholder approval for the
amendment is obtained.
 
     Amendment.  Subject to the applicable provisions of the Massachusetts
General Laws and as may be authorized by their respective Boards of Directors,
the Affiliation Agreement may be amended upon the written agreement of Walden
and UST at any time; provided that any amendment which reduces the amount or
changes the form of the consideration to be delivered to the Walden stockholders
may not be made after the stockholders of Walden have approved the Affiliation
Agreement unless stockholder approval for the amendment is obtained.
 
EXPENSES
 
     The Affiliation Agreement provides that Walden and UST will each pay its
own expenses in connection with the Affiliation, including fees and expenses of
its own financial consultants, accountants and counsel. The expense(s)
associated with printing and distribution of the Registration Statement and this
Joint Proxy Statement - Prospectus will be shared equally by Walden and UST.
 
MANAGEMENT AND OPERATIONS AFTER THE AFFILIATION
 
     UST.  From and after the Effective Time, the UST Board will be expanded by
three members, and Mr. Bradbury and two other individuals selected by Walden and
approved by UST will be elected by the UST Board as directors of UST to fill
existing vacancies on the UST Board with Mr. Bradbury being assigned to the
class of UST directors whose term expires in 2000. Mr. Bradbury shall be
entitled to serve as a member of the UST Steering Committee for so long as he is
a director of UST. Directors of UST who are not otherwise full time officers or
employees of UST or any of its subsidiaries are paid a fee of $250 for each
meeting of the UST Board they attend, plus an annual stipend of $15,000. In
addition, members of the UST Board serving on the Steering Committee receive
additional committee fees in the amount $250 for each meeting of the Steering
Committee they attend.
 
                                       49
<PAGE>   63
 
     Additional information about Mr. Bradbury and the other known individuals
who will serve as the directors and executive officers of UST following the
Affiliation is contained in UST's and Walden's respective Annual Reports on Form
10-K for the year ended December 31, 1995, which are incorporated herein by
reference. See "AVAILABLE INFORMATION" and "INCORPORATION OF CERTAIN INFORMATION
BY REFERENCE."
 
     Walden.  At the Effective Time, the Merger Subsidiary will be merged with
and into Walden, the separate corporate existence of Merger Subsidiary shall
cease to exist, and the surviving corporation will be Walden, as a wholly-owned
subsidiary of UST. At the Effective Time, Walden's legal corporate name shall be
changed to "Mosaic Corp." At the Effective Time, the articles of organization
and By-laws of Walden will become, by amendment, the articles of organization
and By-laws of the Merger Subsidiary. At the Effective Time, subject to the
rights of UST as sole stockholder of Walden, the Merger Subsidiary's officers
and directors immediately prior to the Effective Time shall be the directors of
Walden at the Effective Time and shall hold office subject to Walden's Articles
of Organization and By-laws, as from time to time in effect, and the laws of The
Commonwealth of Massachusetts.
 
     Walden Subsidiaries.  At the Effective Time, the Boards of Directors of
Walden's bank subsidiaries will consist of certain of those directors of such
subsidiaries and such additional persons as selected by UST prior to the
Effective Time to serve as directors of such subsidiaries unless such bank
subsidiaries merge with a UST bank subsidiary as provided for below. At the
written request of UST, Walden has agreed to take or cause to be taken all
necessary actions to effectuate the eventual merger of each of its subsidiary
banks with a subsidiary bank of UST as soon as practicable after the Effective
Time. In the event that Walden's subsidiary banks are merged with and into a UST
subsidiary bank, Mr. Bradbury and the two other individuals selected by Walden
and elected to the UST Board will become directors of the surviving subsidiary
bank.
 
TERMINATION OF THE AFFILIATION AGREEMENT
 
     The Affiliation Agreement may be terminated at any time prior to the
Effective Time, whether before or after the approval by UST and Walden
stockholders of the Affiliation Agreement, the Plan of Merger and each of the
transactions contemplated thereby, under the following circumstances:
 
          (a) by the mutual written consent of UST and Walden authorized by
     their respective Boards of Directors;
 
          (b) by either UST or Walden if (i) the Effective Time shall not have
     occurred on or prior to June 30, 1997, or such later date as shall have
     been agreed to by the parties, (ii) any governmental or regulatory
     authority or agency or court shall have enjoined, denied approval of, or
     otherwise prohibited the consummation of the Affiliation, and such order or
     injunction is final and unappealable, or (iii) if any stockholder approval
     required for the consummation of the Affiliation has not been obtained by
     reason of the failure to obtain the required vote at a duly held meeting of
     stockholders or any adjournment thereof (provided that the terminating
     party is not otherwise in material breach of any representation, warranty,
     covenant, or other agreement contained therein or in the Stock Option
     Agreement);
 
          (c) by either the UST Board or the Walden Board (i) if the other party
     has materially breached any representation, warranty, covenant or other
     agreement contained in the Affiliation Agreement or the Stock Option
     Agreement and such breach is not cured within 45 days after written notice
     thereof is given to the breaching party, or (ii) in the event that any of
     the conditions precedent to the obligations of the terminating party to
     consummate the Affiliation cannot be satisfied or fulfilled by June 30,
     1997 (in either case, provided the terminating party is not otherwise in
     material breach, as determined by the Affiliation Agreement, of any
     representation, warranty, covenant, or other agreement obtained therein or
     in the Stock Option Agreement); or
 
          (d) by written notice of the Walden Board if both (i) the average of
     the per share last reported sale prices of UST Common Stock as reported on
     NASDAQ for the ten consecutive trading day period (the "Determination
     Period") immediately preceding the date of receipt of the last Requisite
     Regulatory Approval (the "Closing Price") is less than $13.81 and (ii) the
     number obtained by dividing the Closing Price by 16.25 is less than the
     number obtained by subtracting (A) 0.15 from (B) the quotient obtained by
     dividing (x) the weighted average of the closing prices of the common stock
     of the 16 comparable
 
                                       50
<PAGE>   64
 
     bank holding companies listed in the Affiliation Agreement for the same
     Determination Period by (y) the weighted average of the closing prices of
     the common stock of the same 16 comparable bank holding companies on August
     29, 1996.
 
     Notwithstanding the foregoing, during the ten (10) business day period
commencing with UST's receipt of Walden's notice of termination pursuant to the
termination provision set forth in paragraph (d) above, UST shall have the
option to increase the consideration to be received by the holders of Walden
Common Stock under the Plan of Merger by adjusting the Conversion Number to
equal the number (calculated to the nearest one-thousandth) obtained by dividing
(x) 26.24 by (y) the Closing Price. If UST so elects within the ten-day period,
it must give prompt written notice to Walden of such election and the revised
Conversion Number, and no termination will have occurred pursuant to the
provision set forth in paragraph (d) above and the Affiliation Agreement will
remain in effect in accordance with its terms (except as the Conversion Number
will have been so modified).
 
                  CERTAIN TERMS OF THE STOCK OPTION AGREEMENT
 
     General.  As a condition to UST's entering into the Affiliation Agreement
and the Plan of Merger, and in consideration therefor (without other
consideration or monetary payment), Walden entered into the Stock Option
Agreement, pursuant to which Walden granted to UST the Option on August 30,
1996. The Stock Option Agreement is intended to protect UST's interests under
the Affiliation Agreement upon the occurrence of certain events which may create
the potential for a third party to acquire or obtain control of Walden. The
Stock Option Agreement may increase the likelihood that the Affiliation will be
consummated by making it more difficult and more expensive for another party to
obtain control of or acquire Walden. Consequently, certain aspects of the Stock
Option Agreement may have the effect of discouraging persons who might now or
prior to the Effective Time be interested in acquiring all of, or a significant
interest in, Walden from considering or proposing such an acquisition, even if
such persons were prepared to pay consideration to Walden's stockholders which
had a higher current market price than the shares of UST Common Stock to be
received for each share of Walden Common Stock pursuant to the Affiliation
Agreement and Plan of Merger. The Stock Option Agreement is attached hereto as
Appendix C.
 
     Grant of Option.  The Option entitles UST to purchase up to 19.9% of the
issued and outstanding and fully paid and non-assessable shares of Walden Common
Stock (the "Option Shares"), or 1,016,868 shares as of August 30, 1996, without
giving effect to any shares subject to or issued pursuant to the Option, at a
price of $20.50 per share (the "Option Price"). The aggregate purchase price for
the original number of Option Shares at the original Option Price is
$20,845,794.
 
     Triggering Events; Exercise of Option.  The Stock Option Agreement provides
that UST may exercise the Option, in whole or in part, if both an Initial
Triggering Event (as defined below) and a Subsequent Triggering Event (as
defined below) shall have occurred prior to the occurrence of an Exercise
Termination Event (as defined below); provided that UST shall have sent to
Walden written notice of such exercise within 30 days following such Subsequent
Triggering Event and prior to the Exercise Termination Event.
 
     For purposes of the Stock Option Agreement:
 
          (a) The term "Initial Triggering Event" means any of the following
     events or transactions occurring after August 30, 1996: (i) Walden, or any
     of its subsidiaries, without UST's prior written consent, enters into an
     agreement to engage in, or the Walden Board recommends approval of, an
     Acquisition Transaction (as defined below) with any person other than UST
     or its subsidiaries; (ii) the stockholders of Walden did not approve the
     Affiliation Agreement at the Walden Meeting, the Walden Meeting was not
     held or was cancelled prior to the termination of the Affiliation Agreement
     or the Walden Board withdrew or modified in an adverse manner to UST its
     recommendation in favor of the Affiliation, in each case after the
     occurrence of any of the following: (A) any person, other than UST or its
     subsidiaries, Walden acting in a fiduciary capacity or a Schedule 13G
     Investor (as defined in the Stock Option Agreement), acquires beneficial
     ownership or the right to acquire beneficial ownership of 10% or more of
     the outstanding shares of Walden Common Stock if such person beneficially
     owned less than 10% on
 
                                       51
<PAGE>   65
 
     August 30, 1996, or acquires beneficial ownership of an additional 3% of
     shares of Walden Common Stock if such person beneficially owned 10% or more
     such shares on August 30, 1996; (B) any person other than UST or its
     subsidiaries has made a bona fide proposal to Walden or its stockholders to
     engage in an Acquisition Transaction by public announcement or written
     communication that is or will become subject to public disclosure; or (C)
     any person, other than UST or its subsidiaries, without UST's consent,
     files an application with any Federal or state bank regulatory authority
     for approval to engage in an Acquisition Transaction; (iii) after any
     person, other than UST or its subsidiaries, has proposed an Acquisition
     Transaction, Walden breaches any covenant or obligation in the Affiliation
     Agreement and such breach (A) would entitle UST to terminate the
     Affiliation Agreement and (B) is not remedied prior to the date of UST's
     notice to Walden of the exercise of the Option; and (iv) any person, other
     than UST or its subsidiaries commences (as defined in Rule 14d-2 under the
     Exchange Act) or files a registration statement under the Securities Act of
     1933, as amended with respect to a tender offer or exchange offer to
     acquire ownership or control of 25% or more, of the then outstanding shares
     of Walden Common Stock. For purposes of the Stock Option Agreement, the
     term "Acquisition Transaction" means (A) a merger or consolidation, or any
     similar transaction, with Walden or any Significant Subsidiary (as such
     term is defined in the Affiliation Agreement) of Walden or any subsidiary
     of Walden which, after such transaction, would be a Significant Subsidiary,
     (B) a purchase, lease or other acquisition of all or substantially all of
     the assets of Walden or any of its Significant Subsidiaries, or (C) a
     purchase or other acquisition of 10% or more of the voting power of Walden
     or any of its Significant Subsidiaries.
 
          (b) The term "Subsequent Triggering Event" means either of the
     following events or transactions occurring after August 30, 1996: (i) the
     acquisition by any person, other than a Schedule 13G Investor, of
     beneficial ownership of 25% or more of the then outstanding shares of
     Walden Common Stock; or (ii) the occurrence of the Initial Triggering Event
     described above in clause (a)(i), except that the percentage referred to in
     subclause (C) of the definition of "Acquisition Transaction" set forth
     above shall be 25%.
 
     For purposes of the Stock Option Agreement, the term "Exercise Termination
Event" shall mean the earliest of: (i) the Effective Time; (ii) termination of
the Affiliation Agreement if such termination occurs prior to an Initial
Triggering Event; or (iii) twelve months after termination of the Affiliation
Agreement if such termination follows an Initial Triggering Event.
 
     As of the date of this Joint Proxy Statement - Prospectus, to the knowledge
of UST and Walden, no Initial Triggering Event or Subsequent Triggering Event
has occurred.
 
     The number of shares of Walden Common Stock subject to the Option will be
increased to the extent that additional shares of Walden Common Stock are issued
or otherwise become outstanding (other than pursuant to an exercise of the
Option), such that, after such issuance, the number of Option Shares will
continue to equal 19.9% of the Walden Common Stock then issued and outstanding
without giving effect to the issuance of any Walden Common Stock subject to the
Option. In the event of any change in the shares of Walden Common Stock by
reason of a stock dividend, split-up, merger, recapitalization, combination,
subdivision, conversion, exchange of shares or similar transaction, the type and
number of Option Shares and the Option Price will be adjusted appropriately. The
Walden Board may make such increases in the number of Option shares, in addition
to those made in accordance with the events described in the immediately
preceding sentence, in order to avoid taxation of any dividend of stock or stock
rights or any event treated as such for federal income tax purposes for the
recipients.
 
     Whenever the number of Option Shares (or other securities) purchasable upon
exercise of the Option is adjusted as provided in the Stock Option Agreement,
the Option Price shall be adjusted by multiplying the Option Price by a
fraction, the numerator of which shall be equal to the number of Option Shares
prior to the adjustment and the denominator of which shall be equal to the
number of Option Shares (or other securities purchasable) after the adjustment.
 
     Repurchase of Option.  Upon the occurrence of a Subsequent Triggering Event
that occurs prior to the occurrence of an Exercise Termination Event, (a) at the
request of UST or any subsequent holder of the Option (each, a "Holder"),
delivered within 30 days of the Subsequent Triggering Event, Walden shall
 
                                       52
<PAGE>   66
 
repurchase the Option from UST or such holder at a price (the "Option Repurchase
Price") equal to the amount by which (i) the market/offer price (as defined
below) exceeds (ii) the Option Price, multiplied by the number of shares for
which the Option may then be exercised, plus UST's or such holder's reasonable
out-of-pocket expenses incurred in connection with the transactions contemplated
by, and the enforcement of UST's rights under, the Affiliation Agreement
including without limitation legal, accounting and investment banking fees (the
"out-of-pocket expenses") and (b) at the request of any owner of Option Shares
(the "Owner"), delivered within 30 days of the Subsequent Triggering Event,
Walden shall repurchase such number of Option Shares from such Owner as the
Owner shall designate at a price (the "Option Share Repurchase Price") equal to
the greater of (i) the market/offer price and (ii) the average exercise price
per share paid by the Owner for the Option Shares so designated, plus UST's
out-of-pocket expenses. The repurchase of an Option by Walden pursuant to the
terms of the Stock Option Agreement may be subject to prior approval of certain
regulatory authorities. See "THE AFFILIATION -- Regulatory Approvals Required
for the Affiliation."
 
     The term "market/offer price" means the highest of (i) the price per share
of Walden Common Stock at which a tender offer or exchange offer therefor has
been made, (ii) the price per share of Walden Common Stock to be paid by any
third party pursuant to an agreement with Walden, (iii) the highest closing
price for shares of Walden Common Stock within the six-month period immediately
preceding the date of the required repurchase of the Options or Option Shares,
as the case may be, or (iv) in the event of a sale of all or a substantial
portion of Walden's assets, the sum of the price paid in such sale for such
assets and the current market value of the remaining assets of Walden as
determined by a nationally recognized investment banking firm selected by a
majority in the interest of the Holders or the Owners as the case may be,
divided by the number of shares of Walden Common Stock outstanding at the time
of such sale. In determining the market/offer price, the value of consideration
other than cash will be determined by a nationally recognized investment banking
firm selected by the Holder or the Owner, as the case may be, and reasonably
acceptable to Walden. However, if Walden at any time after delivery of a notice
of repurchase as described in this paragraph is prohibited under applicable law
or regulation, from delivering to the Holder and/or the Owner, as appropriate,
the Option Repurchase Price and the Option Share Repurchase Price, respectively,
in full, the Holder or Owner may revoke its notice of repurchase of the Option
or the Option Shares either in whole or to the extent of the prohibition,
whereupon, in the latter case, Walden will promptly (I) deliver to the Holder
and/or the Owner, as appropriate, that portion of the Option Repurchase Price or
the Option Share Repurchase Price that Walden is not prohibited from delivering
and (II) deliver, as appropriate, (a) to the Holder, a new Stock Option
Agreement evidencing the right of the Holder to purchase that number of shares
of Walden Common Stock obtained by multiplying the number of shares of Walden
Common Stock for which the surrendered Stock Option Agreement was exercisable at
the time of delivery of the notice of repurchase by a fraction, the numerator of
which is the Option Repurchase Price less the portion thereof theretofore
delivered to the Holder and the denominator of which is the Option Repurchase
Price, or (b) to the Owner, a certificate for the Option Shares it is then so
prohibited from repurchasing.
 
     Conversion of Option.  In the event that prior to an Exercise Termination
Event, Walden enters into any agreement (a) to consolidate with or merge into
any person, other than UST or one of its subsidiaries, such that Walden is not
the surviving corporation, (b) to permit any person, other than UST or one of
its subsidiaries, to merge into Walden and Walden is the surviving corporation,
but in connection with such merger, the then outstanding shares of Walden Common
Stock are changed into or exchanged for stock or other securities of any other
person or cash or any other property, or the outstanding shares of Walden Common
Stock after such merger shall represent less than 50% of the outstanding shares
and share equivalents of the merged corporation, or (c) to sell or otherwise
transfer all or substantially all of its assets to any person, other than UST or
any of its subsidiaries, then, and in each such case, the agreement governing
such transaction must provide that, upon consummation of the transaction, the
Option will be converted into or exchanged for, at the election of UST, an
option (the "Substitute Option") to purchase securities of either the acquiring
person or any person that controls the acquiring person. At the request of the
holder of the Substitute Option, the issuer of the Substitute Option shall
repurchase it at a price, and subject to such other terms and conditions, as set
forth in the Stock Option Agreement.
 
                                       53
<PAGE>   67
 
     Registration Rights.  Within 30 days after the occurrence of a Subsequent
Triggering Event, UST may request Walden to prepare, file and keep current with
respect to the Option and the Option Shares, a registration statement under Rule
415 of the Securities Act with the Commission. Walden is required to use its
best efforts to cause such registration statement first to become effective and
then to remain effective for 180 days or such shorter time as may be reasonably
necessary to effect such sales or other dispositions of Option Shares. UST has
the right to demand two such registrations. The foregoing notwithstanding, if,
at the time of any request by Walden for registration of the Option or the
Option Shares, Walden is in registration with respect to an underwritten public
offering of Walden Common Stock, and if in the good faith judgment of the
underwriter, the inclusion of the Holder's Option or Option Shares would
interfere with the successful marketing of the shares of Walden Common Stock,
the number of Walden Option Shares otherwise to be covered in the registration
may be reduced as provided in the Stock Option Agreement.
 
     Assignment of Option.  Neither UST nor Walden may assign any of its rights
or obligations under the Stock Option Agreement or the Option to any other
person without the express written consent of the other party, except that in
the event a Subsequent Triggering Event occurs prior to an Exercise Termination
Event, UST may assign, with or without Walden's consent but subject to Walden's
right of first refusal as set forth in the Stock Option Agreement, in whole or
in part, its rights and obligations under the Stock Option Agreement or the
Option within 30 days following such Subsequent Triggering Event (or such later
period as provided in the Stock Option Agreement).
 
     Additional Provisions.  Certain rights and obligations of UST and Walden
under the Stock Option Agreement are subject to receipt of required regulatory
approvals. As noted above, the approval of the Federal Reserve Board is required
for the acquisition by UST of more than 5% of the outstanding shares of Walden
Common Stock. Accordingly, UST has included in its application with the Federal
Reserve Board a request for approval of the exercise of its rights under the
Option, including its right to purchase more than 5% of the outstanding shares
of Walden Common Stock. See "THE AFFILIATION -- Regulatory Approvals Required
for the Affiliation."
 
                                       54
<PAGE>   68
 
              UNAUDITED PRO FORMA CONDENSED FINANCIAL INFORMATION
 
                           UST CORP AND SUBSIDIARIES
                     WALDEN BANCORP, INC. AND SUBSIDIARIES
 
             UNAUDITED PRO FORMA CONDENSED COMBINING BALANCE SHEET
 
                               SEPTEMBER 30, 1996
 
     The following Unaudited Pro Forma Condensed Combining Balance Sheet
presents the combined financial position of UST and subsidiaries and Walden and
subsidiaries as of September 30, 1996, assuming the Affiliation had occurred as
of September 30, 1996. The Unaudited Pro Forma Condensed Combining Balance Sheet
also gives effect to the pending acquisition of twenty branches from The First
National Bank of Boston and its parent company, Bank of Boston Corporation,
entered into on June 18, 1996 (the "Branch Purchase") and the sale of UST's
Connecticut banking subsidiary, UST/Conn for cash pursuant to an agreement with
HUBCO, Inc. entered into on August 15, 1996. See "INFORMATION ABOUT UST --
Recent Developments" for a description of the Branch Purchase and the pending
sale of UST/Conn.
 
     The accompanying pro forma information is based on historical balance sheet
data of UST and Walden as of September 30, 1996, giving effect to the proposed
affiliation of UST and Walden under the pooling of interests method of
accounting. The combination of Walden with UST reflects the issuance of 1.9
shares of UST Common Stock in exchange for, and in cancellation of, each
outstanding share of Walden Common Stock. The difference between the par value
of the UST Common Stock to be issued and the par value of the Walden Common
Stock to be acquired ($754,000) has been charged to Additional paid-in-capital.
The Stockholders' investment accounts of Walden reflect the retirement of Walden
Treasury Stock ($4,169,000) upon consummation of the Affiliation through a
charge to Additional paid-in-capital. Pro forma information for the Branch
Purchase is based on estimates available at the date of the execution of the
agreement. UST/Conn balances are historical balances as of September 30, 1996,
adjusted to reflect the resulting deposit premium to be paid and cash to be
received in that transaction under the purchase method of accounting.
 
     The Unaudited Pro Forma Condensed Combining Balance Sheet should be read in
conjunction with the Unaudited Pro Forma Condensed Combined Statements of Income
appearing elsewhere in this Joint Proxy Statement - Prospectus and the
historical financial statements and notes thereto of UST and Walden which are
incorporated by reference in this Proxy Statement/Prospectus. See "INCORPORATION
OF CERTAIN INFORMATION BY REFERENCE." The Unaudited Pro Forma Condensed
Combining Balance Sheet is presented for informational purposes only and is not
necessarily indicative of the combined financial position that would have
occurred if the proposed affiliation of UST and Walden and the Branch Purchase
and sale of UST/Conn had been consummated on September 30, 1996, or at the
beginning of the periods indicated or which may be obtained in the future. For
information regarding the uncertainty of assumptions, estimates and expectations
reflected herein, see "CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING
INFORMATION."
 
                                       55
<PAGE>   69
 
                           UST CORP AND SUBSIDIARIES
                     WALDEN BANCORP, INC. AND SUBSIDIARIES
             UNAUDITED PRO FORMA CONDENSED COMBINING BALANCE SHEET
 
                               SEPTEMBER 30, 1996
 
<TABLE>
<CAPTION>
                               HISTORICAL           PRO FORMA                  BRANCH      UST BANK/     PRO FORMA
                         -----------------------   ADJUSTMENTS   PRO FORMA    PURCHASE    CONNECTICUT   ADJUSTMENTS   PRO FORMA
    (In thousands)          UST         WALDEN     (NOTES 1&2)    COMBINED    (NOTE 3)     (NOTE 4)      (NOTE 4)      COMBINED
                         ----------   ----------   -----------   ----------   ---------   -----------   -----------   ----------
<S>                      <C>          <C>          <C>           <C>          <C>         <C>           <C>           <C>
ASSETS
Cash, due from banks
  and interest bearing
  deposits.............  $   89,741   $   28,775    $ (13,500)   $ 105,016    $  38,900    $     691      $(3,266)    $ 141,341
Excess funds sold......       2,723       15,013                    17,736                    (4,500)                    13,236
Securities
  Available-for-sale...     544,862      172,576                   717,438      140,200      (21,576)                   836,062
  Held to maturity.....                  167,109                   167,109                                              167,109
Loans, net of reserve
  for possible loan
  losses...............   1,317,590      621,847                 1,939,437      510,000      (76,597)      10,000     2,382,840
Premises, furniture and
  equipment............      33,218       12,341                    45,559        4,300         (539)                    49,320
Intangible assets,
  net..................       3,772       13,227                    16,999       60,200                                  77,199
Other real estate
  owned................       1,097        1,245                     2,342                      (274)                     2,068
Other assets...........      38,645       17,260                    55,905        1,700       (1,371)                    56,234
                         ----------   ----------     --------    ----------   ---------    ---------      -------     ----------
        Total assets...  $2,031,648   $1,049,393    $ (13,500)   $3,067,541   $ 755,300    $(104,166)     $ 6,734     $3,725,409
                         ==========   ==========     ========    ==========   =========    =========      =======     ==========
LIABILITIES AND
  STOCKHOLDERS'
  INVESTMENT
Deposits:
  Demand and NOW
    accounts...........  $  518,507   $  182,458                 $ 418,727    $ 378,400    $ (24,310)                 $ 601,416
  Regular savings......     260,459      182,740                   725,437      189,200      (30,983)                 1,055,055
  Money market.........     194,327       76,009                   270,336      154,800       (9,347)                   415,789
  Time deposits........     523,519      318,205                   841,724      137,600      (33,377)                   945,947
                         ----------   ----------                 ----------   ---------    ---------                  ----------
    Total deposits.....   1,496,812      759,412                 2,256,224      860,000      (98,017)                 3,018,207
Short-term
  borrowings...........     314,134       79,899                   394,033     (100,000)      (5,706)                   288,327
Other borrowings.......                  101,426                   101,426                                              101,426
Other liabilities......      30,601       13,607    $  (4,400)      39,808       (1,880)        (443)     $ 2,357        39,842
                         ----------   ----------     --------    ----------   ---------    ---------      -------     ----------
    Total
      liabilities......   1,841,547      954,344       (4,400)   2,791,491      758,120     (104,166)       2,357     3,447,802
Stockholders'
  investment:
  Common stock
    UST................      11,205                     6,074       17,279                                               17,279
    Walden.............                    5,320       (5,320)
  Additional paid-in
    capital............      74,746       38,114       (4,923)     107,937                                              107,937
  Retained earnings....     108,054       56,505       (9,100)     155,459       (2,820)                    4,377       157,016
Unrealized gain (loss)
  on securities
  available for-sale...      (4,339)        (721)                   (5,060 )                                             (5,060 )
  Treasury stock, at
    cost...............                   (4,169)       4,169            0                                                    0
  Deferred compensation
    and other..........         435                                    435                                                  435
                         ----------   ----------     --------    ----------   ---------    ---------      -------     ----------
    Total stockholders'
      investment.......     190,101       95,049       (9,100)     276,050       (2,820)                    4,377       277,607
                         ----------   ----------     --------    ----------   ---------    ---------      -------     ----------
    Total liabilities
      and stockholders'
      investment.......  $2,031,648   $1,049,393    $ (13,500)   $3,067,541   $ 755,300    $(104,166)     $ 6,734     $3,725,409
                         ==========   ==========     ========    ==========   =========    =========      =======     ==========
</TABLE>
 
 See accompanying Notes to Unaudited Pro Forma Condensed Financial Information.
 
                                       56
<PAGE>   70
 
                           UST CORP AND SUBSIDIARIES
                     WALDEN BANCORP, INC. AND SUBSIDIARIES
 
                         UNAUDITED PRO FORMA CONDENSED
                     COMBINED STATEMENTS OF INCOME SUMMARY
 
     The following Unaudited Pro Forma Condensed Combined Statements of Income
give effect to UST's proposed acquisition of Walden by combining the results of
operations of UST for the nine month periods ended September 30, 1996 and 1995,
and for each of the three years ended December 31, 1995, with the results of
operations of Walden for the nine month periods ended September 30, 1996 and
1995, and for each of the three years ended December 31, 1995 (and for periods
prior to 1995, The Co-operative Bank of Concord and The Braintree Savings Bank)
on a pooling of interests basis, assuming the Affiliation had occurred as of the
beginning of each fiscal period. Income (loss) before change in accounting
method per weighted average common shares outstanding are based on the exchange
ratio of 1.9 shares of UST for each share of Walden as specified in the
Affiliation Agreement. The Unaudited Pro Forma Condensed Combined Statements of
Income should be read in conjunction with the Unaudited Pro Forma Condensed
Combining Balance Sheet appearing elsewhere in this Proxy Statement -
Prospectus. See "INCORPORATION OF INFORMATION BY REFERENCE." The Unaudited Pro
Forma Condensed Combining Balance Sheet reflects an after-tax charge for merger
and reorganization expenses of $9.1 million ($13.5 million pre-tax) net of an
estimated 40% tax benefit (after excluding $2.5 million of nondeductible
expense) and an estimated after-tax charge of $2.8 million ($4.7 million
pre-tax) to be taken in connection with the Branch Purchase; however, since
these expenses are nonrecurring, they have not been reflected in the Unaudited
Pro Forma Condensed Combined Statements of Income. The pro forma combined
statements of income do not give effect to any anticipated cost savings in
connection with the merger nor the financial impact of the Branch Purchase or
sale of UST/Conn. The Unaudited Pro Forma Condensed Combined Statements of
Income are presented for information purposes only and are not necessarily
indicative of the combined results of operations that would have occurred if the
proposed merger of UST and Walden had been consummated on September 30, 1996 or
at the beginning of the periods indicated or which may be obtained in the
future. For information regarding the uncertainty of assumptions, estimates and
expectations reflected herein, see "CAUTIONARY STATEMENT REGARDING
FORWARD-LOOKING INFORMATION."
 
                                       57
<PAGE>   71
 
                           UST CORP AND SUBSIDIARIES
                     WALDEN BANCORP, INC. AND SUBSIDIARIES
               PRO FORMA CONDENSED COMBINED STATEMENTS OF INCOME
 
<TABLE>
<CAPTION>
                                                          NINE MONTHS ENDED SEPTEMBER 30, 1996
                                                          -------------------------------------
                                                            UST          WALDEN        COMBINED
                                                          --------       -------       --------
<S>                                                       <C>            <C>           <C>
                                                            (IN THOUSANDS, EXCEPT SHARE DATA)
Interest income:
     Interest and fees on loans.........................  $ 87,963       $41,016       $128,979
     Interest and dividends on securities...............    26,196        14,804         41,000
     Interest on excess funds and other.................       232                          232
                                                          --------       -------       --------
          Total interest income.........................   114,391        55,820        170,211
                                                          --------       -------       --------
Interest expense:
     Interest on deposits...............................    33,182        19,941         53,114
     Interest on borrowings.............................    11,526         6,602         18,137
                                                          --------       -------       --------
          Total interest expense........................    44,708        26,543         71,251
                                                          --------       -------       --------
     Net interest income................................    69,683        29,277         98,960
Provision (credit) for possible loan losses.............   (18,600)          926        (17,674)
                                                          --------       -------       --------
     Net interest income after provision for possible
       loan losses......................................    88,283        28,351        116,634
                                                          --------       -------       --------
Noninterest income:
     Asset management fees..............................     9,518                        9,518
     Fees and charges...................................    10,329         2,593         12,922
     Mortgage loan servicing fees.......................                   1,820          1,820
     Securities gains, net..............................     1,410            40          1,450
     Gain on sale of loans..............................                      16             16
     Other..............................................     1,838           580          2,418
                                                          --------       -------       --------
          Total noninterest income......................    23,095         5,049         28,144
                                                          --------       -------       --------
Noninterest expense:
     Salary and employee benefits.......................    34,454        10,091         44,545
     Occupancy and equipment............................     8,523         3,068         11,592
     Foreclosed asset and workout expense...............     1,433            84          1,517
     Credit card processing expense.....................     3,795                        3,795
     Deposit insurance assessment.......................     4,289             3          4,292
     Other..............................................    15,334         6,093         21,426
                                                          --------       -------       --------
          Total noninterest expense.....................    67,828        19,339         87,167
                                                          --------       -------       --------
Income before taxes.....................................    43,550        14,061         57,611
     Income tax expense.................................    17,251         5,206         22,457
                                                          --------       -------       --------
Income before change in accounting method...............  $ 26,299       $ 8,855       $ 35,154
                                                          ========       =======       ========
Income per share before change in accounting method.....  $   1.45       $  1.65       $   1.24
Weighted average number of common shares outstanding....    18,179         5,377         28,396
</TABLE>
 
      See accompanying Notes to Pro Forma Combined Financial Information.
 
                                       58
<PAGE>   72
 
                           UST CORP AND SUBSIDIARIES
                     WALDEN BANCORP, INC. AND SUBSIDIARIES
 
               PRO FORMA CONDENSED COMBINED STATEMENTS OF INCOME
 
<TABLE>
<CAPTION>
                                                          NINE MONTHS ENDED SEPTEMBER 30, 1995
                                                          -------------------------------------
                                                            UST          WALDEN        COMBINED
                                                          --------       -------       --------
<S>                                                       <C>            <C>           <C>
                                                            (IN THOUSANDS, EXCEPT SHARE DATA)
Interest income:
     Interest and fees on loans.........................  $ 88,979       $40,070       $129,049
     Interest and dividends on securities...............    18,621        12,833         31,454
     Interest on excess funds and other.................     2,415                        2,415
                                                          --------       -------       --------
          Total interest income.........................   110,015        52,903        162,918
                                                          --------       -------       --------
Interest expense:
     Interest on deposits...............................    31,390        19,714         51,104
     Interest on borrowings.............................     6,834         4,770         11,604
                                                          --------       -------       --------
          Total interest expense........................    38,224        24,484         62,708
                                                          --------       -------       --------
     Net interest income................................    71,791        28,419        100,210
Provision for possible loan losses......................    11,290           775         12,065
                                                          --------       -------       --------
     Net interest income after provision for possible
       loan losses......................................    60,501        27,644         88,145
                                                          --------       -------       --------
Noninterest income:
     Asset management fees..............................    10,048                       10,048
     Fees and charges...................................     9,728         2,468         12,196
     Mortgage loan servicing fees.......................                   2,046          2,046
     Securities gains, net..............................     1,786           341          2,127
     Gain on sale of loans..............................                     151            151
     Other..............................................     1,238           303          1,448
                                                          --------       -------       --------
          Total noninterest income......................    22,800         5,309         28,016
                                                          --------       -------       --------
Noninterest expense:
     Salary and employee benefits.......................    33,141         9,923         43,064
     Occupancy and equipment............................     8,268         3,142         11,411
     Foreclosed asset and workout expense...............     4,653           109          4,762
     Credit card processing expense.....................     3,172                        3,172
     Deposit insurance assessment.......................     2,446           905          3,351
     Other..............................................    14,888         6,858         21,652
                                                          --------       -------       --------
          Total noninterest expense.....................    66,568        20,937         87,412
                                                          --------       -------       --------
Income (loss) before taxes..............................    16,733        12,016         28,749
     Income tax expense (benefit).......................     6,274         4,575         10,849
                                                          --------       -------       --------
Income (loss) before change in accounting method........  $ 10,459       $ 7,441       $ 17,900
                                                          ========       =======       ========
Income (loss) per share before change in accounting
  method................................................  $   0.58       $  1.40       $   0.64
Weighted average number of common shares outstanding....    18,030         5,322         28,142
</TABLE>
 
      See accompanying Notes to Pro Forma Combined Financial Information.
 
                                       59
<PAGE>   73
 
                           UST CORP AND SUBSIDIARIES
                     WALDEN BANCORP, INC. AND SUBSIDIARIES
 
               PRO FORMA CONDENSED COMBINED STATEMENTS OF INCOME
 
<TABLE>
<CAPTION>
                                                              YEAR ENDED DECEMBER 31, 1995
                                                          -------------------------------------
                                                            UST          WALDEN        COMBINED
                                                          --------       -------       --------
                                                            (IN THOUSANDS, EXCEPT SHARE DATA)

<S>                                                       <C>            <C>           <C>
Interest income:
     Interest and fees on loans.........................  $118,666       $53,814       $172,480
     Interest and dividends on securities...............    26,256        10,225         36,481
     Interest on excess funds and other.................     3,047         6,914          9,961
                                                          --------       -------       --------
          Total interest income.........................   147,969        70,953        218,922
                                                          --------       -------       --------
Interest expense:
     Interest on deposits...............................    42,683        26,698         69,381
     Interest on short-term borrowings..................     9,281         6,150         15,431
     Interest on other borrowings.......................       571           179            750
                                                          --------       -------       --------
          Total interest expense........................    52,535        33,027         85,562
                                                          --------       -------       --------
     Net interest income................................    95,434        37,926        133,360
Provision for possible loan losses......................    13,090         1,025         14,115
                                                          --------       -------       --------
     Net interest income after provision for possible
       loan losses......................................    82,344        36,901        119,245
                                                          --------       -------       --------
Noninterest income:
     Asset management fees..............................    13,276                       13,276
     Fees and charges...................................    13,166         3,247         16,413
     Mortgage loan servicing fees.......................                   2,737          2,737
     Securities gains, net..............................     1,802           593          2,395
     Gain on sale of loans..............................                     157            157
     Other..............................................     1,726         1,994          3,720
                                                          --------       -------       --------
          Total noninterest income......................    29,970         8,728         38,698
                                                          --------       -------       --------
Noninterest expense:
     Salary and employee benefits.......................    44,287        13,138         57,425
     Occupancy and equipment............................    11,244         4,227         15,471
     Foreclosed asset and workout expense...............     5,784           124          5,908
     Credit card processing expense.....................     4,408                        4,408
     Deposit insurance assessment.......................     3,067           984          4,051
     Other..............................................    19,397        12,160         31,557
                                                          --------       -------       --------
          Total noninterest expense.....................    88,187        30,633        118,820
                                                          --------       -------       --------
Income before taxes.....................................    24,127        14,996         39,123
     Income tax expense.................................     9,169         5,697         14,866
                                                          --------       -------       --------
Income before change in accounting method...............  $ 14,958       $ 9,299       $ 24,257
                                                          ========       =======       ========
Income per share before change in accounting method.....  $   0.83       $  1.74       $   0.86
Weighted average number of common shares outstanding....    18,068         5,352         28,237
</TABLE>
 
      See accompanying Notes to Pro Forma Combined Financial Information.
 
                                       60
<PAGE>   74
 
                           UST CORP AND SUBSIDIARIES
                     WALDEN BANCORP, INC. AND SUBSIDIARIES
 
               PRO FORMA CONDENSED COMBINED STATEMENTS OF INCOME
 
<TABLE>
<CAPTION>
                                                                 YEAR ENDED DECEMBER 31, 1994
                                                                ------------------------------
                                                                  UST       WALDEN    COMBINED
                                                                --------   --------   --------
                                                                 (IN THOUSANDS, EXCEPT SHARE
                                                                            DATA)
<S>                                                             <C>        <C>        <C>
Interest income:
     Interest and fees on loans...............................  $103,526   $ 42,737   $146,263
     Interest and dividends on securities.....................    27,589     10,954     38,543
     Interest on excess funds and other.......................     1,197      6,620      7,817
                                                                --------   --------   --------
          Total interest income...............................   132,312     60,311    192,623
                                                                --------   --------   --------
Interest expense:
     Interest on deposits.....................................    32,907     20,037     52,944
     Interest on short-term borrowings........................     6,240      4,439     10,679
     Interest on other borrowings.............................     1,066        142      1,208
                                                                --------   --------   --------
          Total interest expense..............................    40,213     24,618     64,831
                                                                --------   --------   --------
     Net interest income......................................    92,099     35,693    127,792
Provision for possible loan losses............................    24,281      1,200     25,481
                                                                --------   --------   --------
     Net interest income after provision for possible loan
       losses.................................................    67,818     34,493    102,311
                                                                --------   --------   --------
Noninterest income:
     Asset management fees....................................    14,419                14,419
     Fees and charges.........................................    13,091      2,948     16,039
     Mortgage loan servicing fees.............................                2,491      2,491
     Securities gains, net....................................     1,105        110      1,215
     Gain on sale of loans....................................                  337        337
     Other....................................................     1,719      1,782      3,501
                                                                --------   --------   --------
          Total noninterest income............................    30,334      7,668     38,002
                                                                --------   --------   --------
Noninterest expense:
     Salary and employee benefits.............................    42,650     12,507     55,157
     Occupancy and equipment..................................    11,313      4,029     15,342
     Foreclosed asset and workout expense.....................     8,820        382      9,202
     Credit card processing expense...........................     3,955                 3,955
     Deposit insurance assessment.............................     4,566      1,816      6,382
     Other....................................................    20,051      9,044     29,095
                                                                --------   --------   --------
          Total noninterest expense...........................    91,355     27,778    119,133
                                                                --------   --------   --------
Income before taxes...........................................     6,797     14,383     21,180
     Income tax expense.......................................     2,051      4,895      6,946
                                                                --------   --------   --------
Income before change in accounting method.....................  $  4,746   $  9,488   $ 14,234
                                                                ========   ========   ========
Income per share before change in accounting method...........  $   0.27   $   1.79   $   0.51
Weighted average number of common shares outstanding..........    17,780      5,289     27,829
</TABLE>
 
      See accompanying Notes to Pro Forma Combined Financial Information.
 
                                       61
<PAGE>   75
 
                           UST CORP AND SUBSIDIARIES
                     WALDEN BANCORP, INC. AND SUBSIDIARIES
 
               PRO FORMA CONDENSED COMBINED STATEMENTS OF INCOME
 
<TABLE>
<CAPTION>
                                                              YEAR ENDED DECEMBER 31, 1993
                                                          -------------------------------------
                                                            UST          WALDEN        COMBINED
                                                          --------       -------       --------
                                                            (IN THOUSANDS, EXCEPT SHARE DATA)

<S>                                                       <C>            <C>           <C>
Interest income:
     Interest and fees on loans.........................  $110,673       $40,642       $151,315
     Interest and dividends on securities...............    29,859        10,767         40,626
     Interest on excess funds and other.................        96         5,413          5,509
                                                          --------       -------       --------
          Total interest income.........................   140,628        56,822        197,450
                                                          --------       -------       --------
Interest expense:
     Interest on deposits...............................    40,300        20,715         61,015
     Interest on short-term borrowings..................     6,239         2,742          8,981
     Interest on other borrowings.......................     1,405           152          1,557
                                                          --------       -------       --------
          Total interest expense........................    47,944        23,609         71,553
                                                          --------       -------       --------
     Net interest income................................    92,684        33,213        125,897
Provision for possible loan losses......................    68,427         3,000         71,427
                                                          --------       -------       --------
     Net interest income after provision for possible
       loan losses......................................    24,257        30,213         54,470
                                                          --------       -------       --------
Noninterest income:
     Asset management fees..............................    15,798                       15,798
     Fees and charges...................................    13,721         2,588         16,309
     Mortgage loan servicing fees.......................                   1,699          1,699
     Securities gains, net..............................     4,222           292          4,514
     Gain on sale of loans..............................                   3,041          3,041
     Other..............................................     2,982         1,806          4,788
                                                          --------       -------       --------
          Total noninterest income......................    36,723         9,426         46,149
                                                          --------       -------       --------
Noninterest expense:
     Salary and employee benefits.......................    38,467        10,708         49,175
     Occupancy and equipment............................    11,033         3,672         14,705
     Foreclosed asset and workout expense...............    19,187         1,071         20,258
     Credit card processing expense.....................     3,815                        3,815
     Deposit insurance assessment.......................     4,931         1,947          6,878
     Other..............................................    15,908         7,957         23,865
                                                          --------       -------       --------
          Total noninterest expense.....................    93,341        25,355        118,696
                                                          --------       -------       --------
Income (loss) before taxes..............................   (32,361)       14,284        (18,077)
     Income tax expense (benefit).......................   (11,511)        4,513         (6,998)
                                                          --------       -------       --------
Income (loss) before change in accounting method........  $(20,850)      $ 9,771       $(11,079)
                                                          ========       =======       ========
Income (loss) per share before change in accounting
  method................................................  $  (1.36)      $  1.87       $  (0.44)
Weighted average number of common shares outstanding....    15,362         5,214         25,269
</TABLE>
 
      See accompanying Notes to Pro Forma Combined Financial Information.
 
                                       62
<PAGE>   76
 
          NOTES TO UNAUDITED PRO FORMA CONDENSED FINANCIAL INFORMATION
 
NOTE 1:
 
     It is contemplated that the Affiliation will be accounted for as a pooling
of interests. Accordingly, pro forma financial information assumes that the
Affiliation was consummated as of the beginning of each of the periods indicated
herein. Certain reclassifications have been made to the accounts of Walden in
the accompanying Unaudited Pro Forma Condensed Combining Balance Sheet and
Unaudited Pro Forma Condensed Combined Statements of Income to conform to UST
presentation. Pro forma results of operations do not reflect nonrecurring items
of income and expense relating directly from the proposed Affiliation. In
addition, the accompanying Unaudited Pro Forma Condensed Combined Statements of
Income do not reflect the following: the cumulative effect of an accounting
change to the adoption of Statement of Financial Accounting Standards (SFAS) No.
109, "Accounting for Income Taxes," of $0.75 million for UST for the year ended
December 31, 1993, and the cumulative effect of an accounting change due to the
adoption of SFAS No. 109 of $2.00 million by Walden for the year ended December
31, 1993.
 
     The effect of an estimated one-time after-tax charge of $9.1 million,
($13.5 million pre-tax), to be taken by UST in connection with the Affiliation
has been reflected in the accompanying Unaudited Pro Forma Condensed Combining
Balance Sheet as a reduction in cash and retained earnings, net of a 40% tax
benefit of $4.4 million recorded in other liabilities after excluding $2.5
million of nondeductible expense. The charge has not been reflected in the
Unaudited Pro Forma Condensed Combined Statements of Income since it is
nonrecurring. The pro forma financial information does not give effect to any
cost savings in connection with the Affiliation.
 
NOTE 2:
 
     The pro forma stockholders' investment accounts of UST and Walden have been
adjusted in the accompanying Unaudited Pro Forma Condensed Combining Balance
Sheet to reflect the issuance of shares of UST Common Stock in exchange for all
of the outstanding shares of Walden Common Stock. The number of shares of UST
Common Stock to be issued pursuant to the acquisition of Walden is based upon
the number of Walden shares outstanding as of September 30, 1996, and the
exchange ratio of 1.9 shares of UST Common Stock for each share of Walden Common
Stock as specified in the Affiliation Agreement. The difference between the par
value of the UST Common Stock to be issued ($0.625 per share) and the par value
of the Walden Common Stock to be acquired ($1.00 per share) has been charged to
Additional paid in capital.
 
NOTE 3:
 
     The Unaudited Pro Forma Condensed Combining Balance Sheet includes
adjustments related to an agreement entered into on June 18, 1996, pursuant to
which USTrust will acquire twenty bank branches from The First National Bank of
Boston and BayBank, N.A. In connection with the Branch Purchase, USTrust will
assume approximately $860 million of deposits and will receive approximately
$127.5 million in commercial and industrial loans, $382.5 million of other loans
(primarily 1 to 4 family residential mortgages), certain fixed assets, and the
remainder in cash, net of a deposit premium of 7%. USTrust will not be acquiring
or retaining any management personnel in connection with the Branch Purchase nor
the personnel responsible for originating the majority of the loans to be
acquired in connection with the transaction. Since the Branch Purchase does not
represent the acquisition of a business, separate entity or subsidiary of the
seller, and there are no historical financial statements related thereto, the
effect of the Branch Purchase is not reflected in the Unaudited Pro Forma
Condensed Combined Statements of Income.
 
     The effect of an estimated one-time after-tax charge of $2.8 million ($4.7
million pre-tax), to be taken by UST in connection with the Branch Purchase has
been reflected in the accompanying Unaudited Pro Forma Condensed Combining
Balance Sheet as a reduction in net cash received and retained earnings net of a
40% tax benefit of $1.9 million recorded in other liabilities. The charge has
not been reflected in the Unaudited Pro Forma Condensed Combined Statements of
Income because it is not recurring.
 
                                       63
<PAGE>   77
 
     For additional information concerning the Branch Purchase see "Note 6:
Impact of the Branch Purchase on Operating Performance."
 
NOTE 4:
 
     The Unaudited Pro Forma Condensed Combining Balance Sheet includes
adjustments related to an agreement entered into on August 15, 1996, pursuant to
which UST will sell its Connecticut banking subsidiary, UST/Conn, to HUBCO, Inc.
for cash. The agreement provides, among other matters, that USTrust will
repurchase approximately $10 million in loan participations sold to UST/Conn and
that UST will receive an amount equal to the adjusted Tier 1 capital of UST/Conn
plus a deposit premium of $6.7 million on consummation of the transaction. The
estimated $6.7 million pre-tax gain to be realized in connection with the sale
of UST/Conn has been reflected in the accompanying Unaudited Pro Forma Condensed
Combining Balance Sheet as an increase to cash and an increase in retained
earnings, net of a 35% tax provision, recorded in other liabilities. Net income
for UST/Conn was $0.77 million for the nine months ended September 30, 1996, and
$0.12 million for the year ended December 31, 1995. Accordingly, no adjustment
reflecting the sale of UST/Conn has been reflected in the accompanying Unaudited
Pro Forma Condensed Combined Statements of Income since the operating results of
UST/Conn are not material to the consolidated results of operation.
 
NOTE 5:
 
     Pro forma earnings per share amounts in the accompanying Unaudited Pro
Forma Condensed Combined Statements of Income are based on the weighted average
number of common shares of the constituent companies outstanding during each
period assuming an exchange ratio of 1.9 shares of UST Common Stock for each
share of Walden Common Stock as specified in the Affiliation Agreement.
 
NOTE 6:  IMPACT OF THE BRANCH PURCHASE ON OPERATING PERFORMANCE
 
     The following discussion presents UST's current assessment of the possible
incremental impact of the purchase by USTrust of twenty bank branches of The
First National Bank of Boston and BayBank, N.A. (the "Branch Purchase") on the
operating performance of UST, taking into account the transfer to, and
assumption by, USTrust of certain assets and liabilities as set forth in the
Purchase and Assumption Agreement dated as of June 18, 1996 (as amended, the
"Purchase Agreement") between UST and The First National Bank of Boston ("FNBB")
and joined in for certain limited purposes by its parent corporation, Bank of
Boston Corporation ("Bank of Boston"). This section contains or reflects certain
forward-looking information regarding future performance of UST and the possible
effect of the Branch Purchase on UST. The actual effect of the Branch Purchase
may vary significantly from this assessment due to a number of factors beyond
UST's control, such as interest rate levels, earning asset/interest bearing
liability balances and mix, regional economic conditions and the actual amount
of noninterest income and expense. As a result, there can be no assurance that
the effect of the Branch Purchase will be as anticipated by UST.
 
     Assets Purchased and Liabilities Assumed.  Under the terms of the Purchase
Agreement, USTrust has agreed to purchase certain assets and assume the deposit
and certain other liabilities attributed to twenty branch banking offices of
FNBB and BayBank, N.A. Four of the branches are offices of FNBB and sixteen
branches are offices of BayBank, N.A., which are indirectly owned by Bank of
Boston as a result of the merger of BayBank, N.A.'s parent, BayBanks, Inc., with
and into a special purpose wholly-owned subsidiary of Bank of Boston. Pursuant
to the Branch Purchase, UST will assume approximately $860 million in deposit
liabilities attributed to the twenty branches ("Assumed Deposits").
Historically, approximately 44% of the Assumed Deposits are comprised of demand
deposits and NOW accounts, while 39% are represented by savings and money market
accounts, and 17% are in the form of time deposits. The historical interest rate
paid on these deposits approximates 280 basis points. Upon consummation of the
Branch Purchase, UST expects to acquire a portfolio of commercial and industrial
loans of approximately $127.5 million and $382.5 million of other loans (one- to
four-family residential loans, reserve credit and home equity loans) (together
with the commercial and industrial loans, the "Purchased Loans") equal to
approximately $510.0 million; certain fixed
 
                                       64
<PAGE>   78
 
assets, comprised of owned and leased premises, improvements and equipment; and
cash, net of a premium equal to 7 percent of the Assumed Deposits.
 
     USTrust has applied for and received the approval of the FDIC and the
Massachusetts Commissioner of Banks to consummate the Branch Purchase. As a
condition to the FDIC approval however, USTrust must have a Tier 1 Capital Ratio
of not less than (a) 4.8%, no later than ten days after consummation of the
acquisition of the sixteen BayBank, N.A. branches to be acquired; and (b) 5%, no
later than three months after consummation of the acquisition of the BayBank,
N.A. branches and for a period of six months thereafter. UST currently
anticipates that USTrust will achieve and maintain Tier 1 Capital Ratios equal
to or in excess of the foregoing conditions. In addition, UST expects that the
foregoing conditions will not have a material adverse impact on the operations
of USTrust after the Branch Purchase.
 
     Balance Sheet Adjustments.  The Purchase Agreement provides that the
Purchased Loans shall be at a value equal to the unpaid principal balance plus
accrued interest thereon and that real property, other assets and cash, net of
the 7 percent deposit premium, shall be purchased at a price equal to the book
value thereof. Prior to consummation of the Branch Purchase, appraisals will be
conducted of the assets to be acquired and, upon the completion of such
appraisals, a portion of the purchase price will be allocated to tangible assets
and purchased mortgage servicing rights, to be amortized over their remaining
estimated lives.
 
     For purposes of the Unaudited Pro Forma Condensed Combining Balance Sheet,
the balances have been allocated as follows:
 
<TABLE>
<CAPTION>
      (IN THOUSANDS)             AMOUNT           PERCENT
                             --------------       -------
<S>                          <C>                  <C>
Commercial loans...........     $127,500            14.8%
Other loans................      382,500            44.5
Cash (invested as
  short-term securities)...      140,200            16.3
Cash used to retire
  interest bearing
  liabilities..............      100,000            11.6
Deposit premium............       60,200(a)          7.0
Branch cash and float......       43,600             5.1
Fixed assets...............        4,300             0.5
Other assets...............        1,700             0.2
                             --------------       -------
    Totals.................     $860,000           100.0%
                             ==============       =======
Deposits:
    Demand and NOW.........     $378,400            44.0%
    Regular Savings........      189,200            22.0
    Money market...........      154,800            18.0
    Time deposits..........      137,600            16.0
                             --------------       -------
                                $860,000           100.0%
                             ==============       =======
</TABLE>
 
- ---------------
 
(a) A final allocation of this premium is expected to result in a reduction of
    the intangible and an increase in other assets as described above.
 
     Net Interest Income.  It is expected that of the approximately $240.2
million net cash to be received by USTrust in the Branch Purchase, in excess of
float and cash required to operate the branches, $140.2 million will be invested
in short-term (two years or less) U.S. Treasury or Agency securities at a yield
of 6.00% and $100.0 million will be used to reduce interest bearing liabilities
at current rates of 5.5%. Although USTrust's review of the commercial and
industrial loans to be purchased has not been completed as of the date of this
Joint Proxy Statement - Prospectus, it is anticipated that the current yield on
this portfolio will approximate 9.25%. Other loans to be purchased by USTrust,
comprised primarily of residential mortgage loans and loans with related branch
deposits (home equity credit lines and overdraft checking), will approximate
$382.5 million and the portfolio is expected to produce an initial yield of
approximately 7.50%. As noted above, the deposit liabilities to be assumed carry
a historical cost of approximately 2.80%. As a result of the likelihood that, as
is customary in transactions of the type of the Branch Purchase, a number of
depositors at the branches to be purchased may elect to continue their
relationships with FNBB or BayBank, N.A., as applicable, or remove their
accounts from a branch for other reasons, UST has assumed a probable run-off of
accounts of 10%. UST also assumes that it will retain the existing level of
earning assets at a comparable yield and mix and replace the deposit run-off
with higher yielding deposits at a cost of 5.0%. As a result, the effective cost
of funds on the Assumed Deposits would increase from 2.80% to approximately
3.0%. Based upon the preceding assumptions, UST estimates that the Purchased
Loans, short-term investments and
 
                                       65
<PAGE>   79
 
Assumed Deposits would combine to produce additional net interest income on an
annualized basis of approximately $28.6 million.
 
<TABLE>
<CAPTION>
                                                                      INTEREST INCOME/
                      (IN THOUSANDS)               BALANCE    RATE       (EXPENSE)
                                                   --------   -----   ----------------
          <S>                                      <C>        <C>     <C>
          Commercial and industrial loans........  $127,500    9.25%      $ 11,800
          Other loans............................   382,500    7.50         28,700
          Short-term investments.................   140,200    6.00          8,425
          Pay-down of interest bearing
            liabilities..........................   100,000    5.50          5,500
          Deposit liabilities....................   860,000    3.00        (25,800)
                                                                      ----------------
          Net interest income....................                         $ 28,625
                                                                      ===============
</TABLE>
 
     The foregoing table contains or reflects forward-looking information
regarding the actual effect of the Branch Purchase on net interest income of
UST. The actual amount of net interest income may vary significantly from the
amounts set forth above. The foregoing table assumes no significant variations
in interest rates or asset/liability volume or mix since UST is not in a
position to predict future interest rates or customer balances. Interest rate
movements may occur at different frequency and in different amounts from those
assumed by UST, and assets and liabilities may reprice at maturity or on
repricing dates at rates lower or higher than those in effect on any given
measurement date. Accordingly, no assurance can be made that these estimates
will be indicative of actual results.
 
     Provision for Possible Loan Losses.  USTrust estimates that it will
allocate approximately $6.4 million from the unallocated portion of its existing
reserve for possible loan losses to the $510 million of Purchased Loans. As
provided in the Purchase Agreement, USTrust may elect not to purchase any
commercial loan attributable to a branch to be purchased if (i) such loan has a
credit or documentation deficiency; (ii) such loan is rated less than
"Satisfactory" under the FNBB's or BayBank, N.A.'s (as applicable) internal loan
rating system; or (iii) such loan is unrated and is deemed substandard by
USTrust under certain conditions. Additionally, USTrust may reject a residential
real estate loan that is sixty days or more past due. USTrust has assumed that
all Purchased Loans will initially qualify as "Satisfactory" under USTrust's
internal risk rating system thereby requiring an initial reserve allocation of
1.25% of the principal balance. Future provisions for possible loan losses
related to the portfolio of Purchased Loans, which are estimated at 25 basis
points for purposes of the Proxy Statement - Prospectus, will be based on actual
performance, delinquency, regional economic conditions and other factors.
 
     Noninterest Income.  USTrust expects to realize noninterest income from the
Branch Purchase primarily in the form of deposit service charges and expects to
match a number of products and service charge schedules while offering both
value and convenience options designed to retain deposits. USTrust estimates
that deposit service charges, overdraft fees and related income will increase by
approximately $6.0 million on an annualized basis as a result of the Branch
Purchase.
 
     Noninterest Expense.  USTrust expects to incur approximately $22.7 million
of additional noninterest expense during the first full year of operation
following the Branch Purchase. The additional noninterest expense consists of
existing branch overhead of $6.9 million (approximately $350 thousand per branch
including personnel expense, occupancy expense, equipment expense and other
direct operating costs), incremental operating expenses of $8.4 million
necessary to support the additional activity in the operations area, and an
estimated $7.4 million representing the first year charge for the amortization
of intangible assets.
 
     The $8.4 million estimate for incremental expense includes the following:
(i) $3.0 million in personnel costs and support systems for additional check
processing volumes, (ii) an estimated $4.4 million to support additional retail
banking operations (staff additions, marketing and communication costs, foreign
ATM fees, branch automation and other direct expenses), and (iii) approximately
$1 million for other costs related to loan servicing facilities management and
other support functions.
 
     The $7.4 million charge to be recorded for the amortization of intangibles
assumes a balance at acquisition of $60.2 million with a twelve year accelerated
amortization.
 
     Income Taxes.  Taxes are calculated at an assumed combined Federal and
State rate of 40%.
 
                                       66
<PAGE>   80
 
     Summary Impact of Branch Purchase on Operating Performance.  The following
table summarizes the expected effect, subject to the qualifications set forth
above, of the Branch Purchase on the operating performance of UST and USTrust
during the first full year of operation of the branches under the management of
UST and USTrust.
 
<TABLE>
          <S>                                                               <C>
          Net interest income.............................................  $28,625
          Provision for possible loan losses..............................   (1,275)
                                                                            -------
          Net interest income after provision for loan losses.............  $27,350
          Noninterest income..............................................    6,000
          Noninterest expense:
            Existing branch overhead......................................   (6,900)
            Incremental expenses..........................................   (8,400)
            Amortization of intangible assets.............................   (7,400)
                                                                            -------
          Income before income taxes......................................   10,650
          Income tax provision............................................   (4,250)
                                                                            -------
          Income from operations..........................................  $ 6,400
                                                                            =======
</TABLE>
 
     In addition to the above, USTrust expects to record a pre-tax charge of
approximately $4.7 million of nonrecurring charges at consummation for
expenditures such as customer communications, new customer checkbooks,
replacement ATM and debit cards, acquisition advertising, business development
and expenses related to loan redocumentation and appraisals.
 
     The foregoing table contains or reflects certain forward-looking
information regarding the future performance of UST and USTrust and the actual
effect of the Branch Purchase on UST and USTrust. The actual effect of the
Branch Purchase may vary significantly from this assessment due to a number of
factors beyond UST's control, such as interest rate levels, earning
asset/interest bearing liability balances and mix, regional economic conditions
and the actual amount of noninterest income and expense. As a result,
shareholders of UST and Walden must recognize that there can be no assurance
that the effect of the Branch Purchase will be as anticipated by UST.
 
                                       67
<PAGE>   81
 
                       CERTAIN REGULATORY CONSIDERATIONS
 
GENERAL
 
     As bank holding companies registered under the Bank Holding Company Act of
1956, as amended (the "BHCA"), UST and Walden are subject to substantial
regulation and supervision by the Federal Reserve Board. As state-chartered
banks, USTrust, United States Trust Company, UST Bank/Conn, Concord and
Braintree are subject to substantial regulation and supervision by the FDIC and
by applicable state regulatory agencies. To the extent that the following
information describes statutory or regulatory provisions, it is qualified in its
entirety by reference to those particular statutory or regulatory provisions.
Any change in applicable law or regulation may have a material effect on the
business and prospects of UST and Walden. See "CERTAIN REGULATORY CONSIDERATIONS
- -- Legislation and Related Matters." For a more complete description of specific
regulatory matters relating to UST and Walden, see the UST Annual Report and the
Walden Annual Report respectively, on Form 10-K filed for the fiscal year ended
December 31, 1995.
 
     UST and Walden are required by the BHCA to file with the Federal Reserve
Board an annual report and such additional reports as the Federal Reserve Board
may require. The Federal Reserve Board also makes periodic inspections of UST,
Walden and their subsidiaries. The BHCA requires every bank holding company to
obtain the prior approval of the Federal Reserve Board before it may acquire
ownership or control of any voting shares of any bank, if, after such
acquisition, it would own or control, directly or indirectly, more than 5
percent of the voting shares of such bank. Additionally, as bank holding
companies, UST and Walden are prohibited from acquiring ownership or control of
5% or more of any company not a bank or from engaging in activities other than
banking or controlling banks except where the Federal Reserve Board has
determined that such activities are so closely related to banking as to be a
"proper incident thereto."
 
     Because UST and Walden are also bank holding companies under the
Massachusetts General Laws, the Massachusetts Commissioner has authority to
require certain reports from UST and Walden from time to time and to examine UST
and Walden and each of their subsidiaries. In August 1996, Massachusetts adopted
legislation which will allow well-capitalized banks to be inspected by
Massachusetts regulators once every 18 months in contrast to the current yearly
examination. Prior approval of the Massachusetts Board of Bank Incorporation is
also required before UST and Walden may acquire any additional financial
institutions located in Massachusetts or in those states which permit
acquisitions of banking institutions located in their states by Massachusetts
bank holding companies. See "CERTAIN REGULATORY CONSIDERATIONS -- Legislation
and Related Matters -- Interstate Banking Legislation."
 
     Neither UST, Walden nor any of their subsidiaries is subject to any formal
written agreements with state and federal regulators. See "CERTAIN REGULATORY
CONSIDERATIONS -- Legislation and Related Matters -- Capital Guidelines."
 
DIVIDENDS
 
     General.  UST and Walden are each legal entities separate and distinct from
their subsidiary banks and other nonbank subsidiaries. The revenues of UST and
Walden (on a parent company only basis) are derived primarily from interest and
dividends paid to the corporations by their respective subsidiaries. The right
of UST and Walden, and consequently the right of stockholders of UST and Walden,
to participate in any distribution of the assets or earnings of any subsidiary
through the payment of such dividends or otherwise is necessarily subject to the
prior claims of creditors of the subsidiary (including depositors, in the case
of banking subsidiaries), except to the extent that certain claims of UST or
Walden in a creditor capacity may be recognized.
 
     The payment of dividends by UST and Walden is determined by their
respective boards of directors based on UST and Walden's liquidity, asset
quality profile, capital adequacy, and recent earnings history, as well as
economic conditions and other factors, including applicable government
regulations and policies and the amount of dividends payable to UST and Walden
by their respective subsidiaries.
 
     As set forth in the Affiliation Agreement, UST and Walden have agreed that
Walden may continue to pay a regular quarterly cash dividend to its shareholders
at a rate not exceeding its current dividend rate,
 
                                       68
<PAGE>   82
 
provided that Walden and UST mutually coordinate payment of such dividend with
the payment by UST of a dividend to UST's shareholders.
 
     It is the policy of the Federal Reserve Board that banks and bank holding
companies, respectively, should pay dividends only out of current earnings and
only if after paying such dividends the bank or bank holding company would
remain adequately capitalized. Federal banking regulators also have authority to
prohibit banks and bank holding companies from paying dividends if they deem
such payment to be an unsafe or unsound practice. In addition, it is the
position of the Federal Reserve Board that a bank holding company is expected to
act as a source of financial strength to its subsidiary banks.
 
     State law requires the approval of state bank regulatory authorities if the
dividends declared by state banks exceed prescribed limits. As of October 31,
1996, an aggregate of approximately $8.5 million of dividends were declared and
paid by UST's bank and nonbank subsidiaries. As of October 31, 1996, an
aggregate of approximately $13.0 million of dividends were declared and paid by
Walden's bank and nonbank subsidiaries. The payment of any future dividends by
UST and Walden's subsidiaries will be determined based on a number of factors,
including the subsidiary's liquidity, asset quality profile, capital adequacy
and recent earnings history.
 
     In connection with the Branch Purchase, USTrust has applied for and
received the approval of the FDIC and the Massachusetts Commissioner to
consummate such acquisition. However, as a condition to FDIC approval with
respect to the sixteen BayBank, N.A. branches to be acquired, USTrust must
comply with certain capital maintenance requirements at and within the first six
months after consummation of the acquisition of the BayBank branches. Therefore,
payment of dividends to UST by USTrust, and consequently payment of dividends to
UST stockholders by UST, may be limited to the extent required to achieve
compliance with the FDIC conditions to approval. See "CERTAIN REGULATORY
CONSIDERATIONS -- Legislation and Related Matters -- Capital Guidelines."
Because alternative ways of achieving the required minimum exist, however,
management of UST does not currently contemplate any such dividend limitation as
a result of the Branch Purchase. See "CAUTIONARY STATEMENT REGARDING
FORWARD-LOOKING INFORMATION."
 
LEGISLATION AND RELATED MATTERS
 
     General.  In addition to extensive existing government regulation, federal
and state statutes and regulations are subject to changes that may have
significant impact on the way in which banks may conduct business. The
likelihood and potential effects of any such changes cannot be predicted.
Legislation enacted in recent years has substantially increased the level of
competition among commercial banks, thrift institutions and non-banking
institutions, including insurance companies, brokerage firms, mutual funds,
investment banks, finance companies and major retailers. In addition, the
existence of banking legislation such as the Financial Institutions Reform,
Recovery and Enforcement Act of 1989 ("FIRREA") and the Federal Deposit
Insurance Corporation Improvement Act of 1991 ("FDICIA") have affected the
banking industry by, among other things, broadening the regulatory powers of the
federal banking agencies in a number of areas. The following summary is
qualified in its entirety by the text of the relevant statutes and regulations.
 
     FIRREA.  As a result of the enactment of FIRREA on August 9, 1989, any or
all of UST or Walden's subsidiary depository institutions can be held liable for
any loss incurred by, or reasonably expected to be incurred by, the FDIC after
August 9, 1989, in connection with (a) the default of any other of UST's or
Walden's subsidiary depository institutions or (b) any assistance provided by
the FDIC to any other of UST's or Walden's subsidiary depository institutions in
danger of default. "Default" is defined generally as the appointment of a
conservator or receiver and "in danger of default" is defined generally as the
existence of certain conditions indicating that a "default" is likely to occur
without regulatory assistance.
 
     FDICIA.  FDICIA, which was enacted on December 19, 1991, provides for,
among other things, increased funding for the Bank Insurance Fund (the "BIF") of
the FDIC and expanded regulation of depository institutions and their
affiliates, including parent holding companies. A summary of certain material
provisions of FDICIA and its regulations is provided below.
 
                                       69
<PAGE>   83
 
     Prompt Corrective Action.  FDICIA provides the federal banking agencies
with broad powers to take prompt corrective action to resolve problems of
insured depository institutions, depending upon a particular institution's level
of capital. The FDICIA establishes five tiers of capital measurement for
regulatory purposes ranging from "well-capitalized" to "critically
undercapitalized." A depository institution may be deemed to be in a
capitalization category that is lower than is indicated by its actual capital
position under certain circumstances. As of June 30, 1996, each of UST and
Walden's subsidiary depository institutions were classified as
"well-capitalized" under the applicable prompt corrective action regulations.
 
     Brokered Deposits.  Under FDICIA, a depository institution that is
well-capitalized may accept brokered deposits. A depository institution that is
adequately capitalized may accept brokered deposits only if it obtains a waiver
from the FDIC, and may not offer interest rates on deposits "significantly
higher" than the prevailing rate in its market. An undercapitalized depository
institution may not accept brokered deposits.
 
     Safety and Soundness Standards.  FDICIA, as amended, directs each federal
banking agency to prescribe safety and soundness standards for depository
institutions relating to internal controls, information systems, internal audit
systems, loan documentation, credit underwriting, interest rate exposure, asset
growth, compensation, asset-quality, earnings and stock valuation. The Community
Development and Regulatory Improvement Act of 1994 amended FDICIA by allowing
federal banking activities to publish guidelines rather than regulations
concerning safety and soundness.
 
     The Federal Reserve Board has finalized these safety and soundness
guidelines. These guidelines relate to the management policies of financial
institutions and are designed, in large part, to implement the safety and
soundness criteria outlined in FDICIA. These guidelines will be published after
the other federal bank regulatory agencies have developed their guidelines. At
this time, it is not known what effect the applicable guidelines will have on
the current practices of UST, Walden or their subsidiaries.
 
     FDICIA also contains a variety of other provisions that may affect UST,
Walden or their subsidiaries' respective operations, including reporting
requirements, regulatory guidelines for real estate lending, "truth in savings"
provisions, and the requirement that a depository institution give 90 days'
prior notice to customers and regulatory authorities before closing any branch.
Certain of the provisions in FDICIA have recently been or will be implemented
through the adoption of regulations by the various federal banking agencies and,
therefore, their precise impact cannot be assessed at this time.
 
     Capital Guidelines.  Under the uniform capital guidelines adopted by the
federal banking agencies, a well-capitalized institution must have a minimum
ratio of total capital to risk-adjusted assets (including certain off-balance
sheet items, such as standby letters of credit) of 10%, a minimum Tier 1
(comprised of common equity, retained earnings, minority interests in the equity
accounts of consolidated subsidiaries and a limited amount of noncumulative
perpetual preferred stock, less deductible intangibles) capital-to-total risk
based assets of 6% and a minimum leverage ratio (Tier 1 capital to average
quarterly assets, net of goodwill).
 
     As of June 30, 1996, each of USTrust, USTC and UST/Conn were classified as
"well-capitalized." As of June 30, 1996, Concord and Braintree were each
classified as "well-capitalized."
 
     In connection with the Branch Purchase, USTrust has applied for and
received the approval of the FDIC and The Massachusetts Commissioner to
consummate the acquisition. However, as a condition to FDIC approval with
respect to the sixteen BayBank branches to be acquired in the Branch Purchase,
USTrust must have a Tier 1 Capital Ratio of not less than (i) 4.8%, no later
than ten days after consummation of the acquisition of the BayBank branches and
(ii) 5%, no later than three months after consummation of the acquisition of the
BayBank branches and for a period of six months thereafter. Other than as set
forth above, neither UST nor Walden nor any of their subsidiaries is subject to,
or party to, any order or agreement with any federal banking agency with respect
to the capital maintenance.
 
     The federal banking agencies continue to indicate their desire to raise
capital requirements applicable to banking organizations, and recently proposed
amendments to their risk-based capital regulations to provide for the
consideration of interest rate risk in the determination of a bank's minimum
capital requirements. The proposed amendments are intended to require that banks
effectively measure and monitor their interest rate risk and that they maintain
capital adequate for that risk. Under the proposed amendments, banks with
 
                                       70
<PAGE>   84
 
interest rate risk in excess of a defined supervisory threshold would be
required to maintain additional capital beyond that generally required. In
addition, effective January 17, 1995, the federal banking agencies adopted
amendments to their risk-based capital standards to provide for the
concentration of credit risk and certain risks arising from nontraditional
activities, as well as a bank's ability to manage these risks, as important
factors in assessing a bank's overall capital adequacy.
 
     Under federal banking laws, failure to meet the minimum regulatory capital
requirements could subject a banking institution to a variety of enforcement
remedies available to federal regulatory authorities, including the termination
of deposit insurance by the FDIC and seizure of the institution.
 
     Community Reinvestment Act.  Pursuant to the Community Reinvestment Act
("CRA") and similar provisions of Massachusetts and Connecticut law (with
respect to UST/Conn), regulatory authorities review the performance of UST,
Walden and their subsidiary banks in meeting the credit needs of the communities
served by the subsidiary banks. The applicable regulatory authorities consider
compliance with this law in connection with applications for, among other
things, approval of branches, branch relocations and acquisitions of banks and
bank holding companies. USTrust and UST/Conn both received "outstanding" ratings
from the FDIC at their most recent CRA examinations. Concord and Braintree both
received "outstanding" ratings at their most recent FDIC CRA examinations.
Concord and Braintree both received "satisfactory" ratings at their most recent
Massachusetss CRA examination. In 1995, the FDIC adopted new regulations whereby
an institution that offers a narrow product line to a regional or broader market
can apply for status as a "Limited Purpose Institution" and be examined as such
by the FDIC and CRA compliance. United States Trust Company will apply for this
status since its focus is only upon trust and asset management activities. The
Massachusetts Commissioner has continued to examine USTC for CRA compliance, and
currently rates USTC "satisfactory."
 
     Interstate Banking Legislation.  The Interstate Banking and Branching
Efficiency Act of 1994 facilitates the interstate expansion and consolidation of
banking organizations by permitting (i) beginning one year after enactment of
the legislation, bank holding companies that are adequately capitalized and
managed to acquire banks located in states outside their home states regardless
of whether such acquisitions are authorized under the law of the host state,
(ii) the interstate merger of banks after June 1, 1997, subject to the right of
individual states to "opt in" or "opt out" of this authority prior to such date,
(iii) banks to establish new branches on an interstate basis provided that such
action is specifically authorized by the law of the host state, (iv) foreign
banks to establish, with approval of the appropriate regulators in the United
States, branches outside their home states to the same extent that national or
state banks located in such state would be authorized to do so and (v) banks to
receive deposits, renew time deposits, close loans, service loans and receive
payments on loans and other obligations as agent for any bank or thrift
affiliate, whether the affiliate is located in the same or different state.
 
     In August 1996, Massachusetts enacted legislation implementing the
provisions of the Interstate Banking Act. In the new legislation, Massachusetts
authorized immediate "opt in" to interstate banking. Thus, the new legislation
substantially facilitates the geographic expansion of banking by Massachusetts
and out-of-state banks.
 
     The new legislation allows out-of-state banks to establish and maintain
branches through a merger or consolidation with or the purchase of assets or
stock of any Massachusetts bank or through de novo branch establishment or
purchase of a branch without purchase of the bank which owns the branch, in
Massachusetts, provided that such out-of-state bank is expressly authorized to
do so by the laws of the state under which it is organized. The new legislation
also allows Massachusetts banks to establish and maintain branches through a
merger or consolidation with or by the purchase of the whole or any part of the
assets or stock of any out-of-state bank or through de novo branch establishment
in any other state other than Massachusetts. Finally, the new legislation
prohibits the establishment of bank holding companies and acquisition of banks
and bank holding companies by Massachusetts and out-of-state bank holding
companies if the Massachusetts bank to be acquired has been in existence less
than 3 years or if, after such acquisition, the bank holding company
 
                                       71
<PAGE>   85
 
would control 28% of the deposits in Massachusetts (until 1998, when the deposit
limitation is increased to 30%).
 
     Federal Home Loan Bank System.  The Federal Home Loan Bank of Boston
("FHLBB") provides a central credit facility for member institutions. As members
of the FHLBB, USTrust, Concord and Braintree are required to acquire and hold
shares of capital stock in that bank in an amount at least equal to 1% of the
aggregate principal amount of its unpaid residential mortgage loans, home loan
purchase contracts, and similar obligations at the end of each calendar year, or
1/20 of its advance from the FHLBB, whichever is greater.
 
     Savings Association Insurance Fund.  In September 1996, legislation was
enacted by Congress providing for the recapitalization of the Savings
Association Insurance Fund ("SAIF"). Savings associations and commercial banks
holding SAIF-insured deposits will be assessed a one-time charge in connection
with the servicing of the debt incurred with respect to the thrift bailout
through the issuance of FICO bonds. USTrust acquired SAIF-insured deposits,
indirectly through an affiliate on September 7, 1990, when it assumed certain
deposits and liabilities of the failed Home Owners Federal Loan Bank, FSB, from
the Resolution Trust Company. As a result, USTrust expects to accrue a one-time
charge of $3 million during the quarter ended September 30, 1996, representing
its current estimate of the SAIF assessment, to be paid by December 31, 1996.
 
OTHER PROPOSALS
 
     Other legislative and regulatory proposals regarding changes in banking,
and the regulation of banks and other financial institutions, are regularly
considered by the executive branch of the federal government, Congress and
various state governments, including Massachusetts, and state and federal
regulatory authorities. It cannot be predicted what additional legislative
and/or regulatory proposals, if any, will be considered in the future, whether
any such proposals will be adopted or, if adopted, how any such proposals would
affect UST or Walden or their respective subsidiaries.
 
                                       72
<PAGE>   86
 
                        DESCRIPTION OF UST CAPITAL STOCK
 
GENERAL
 
     The Company is authorized by its Articles of Organization to issue
30,000,000 shares of UST Common Stock and 4,000,000 shares of preferred stock
(the "Preferred Stock"). As of the Record Date, there were outstanding
17,936,989 shares of UST Common Stock and no shares of Preferred Stock.
 
COMMON STOCK
 
     Dividend Rights.  The ability of UST and its bank subsidiaries to pay
dividends is subject to certain limitations imposed by statutes of The
Commonwealth of Massachusetts and certain restrictions imposed by regulatory
authorities. Generally, with respect to the bank subsidiaries, the payment of
dividends is limited by statute to the amount of retained earnings, after
deducting losses and statutorily defined bad debts in excess of established
allowances for loan losses. As a condition to the FDIC's approval of the Branch
Purchase, UST's lead bank subsidiary, USTrust must maintain certain prescribed
capital levels until six months after the consummation of the Branch Purchase.
Therefore, to the extent that the payment of dividends to UST by USTrust would
negatively impact USTrust's ability to meet those capital levels, USTrust may
limit such payments accordingly. Any such limits on the payment of dividends to
UST may limit UST's ability to pay dividends to its stockholders during the
prescribed time period. See "CERTAIN REGULATORY CONSIDERATIONS -- Dividends" for
a discussion of the condition. However, management of UST does not currently
contemplate any such dividend limitation as a result of the Branch Purchase. See
"CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING INFORMATION." When, as and if
dividends, payable in cash, stock or other property, are declared by the UST
Board out of funds legally available therefor, the holders of UST Common Stock
are entitled to share equally, share for share, in such dividends.
 
     Voting Rights.  Holders of UST Common Stock are entitled to one vote for
each share on all matters voted upon by stockholders. Shares of UST Common Stock
have non-cumulative voting rights, which means that the holders of more than 50%
of the shares voting in an election of directors can elect 100% of the directors
being elected if they choose to do so.
 
     Preemptive Rights.  Authorized shares of UST Common Stock may be issued at
any time, and from time to time, in such amounts and for such consideration as
may be fixed by the UST Board. No holder of UST Common Stock has any preemptive
or preferential right to purchase or to subscribe for any shares of capital
stock or other securities which may be issued by UST.
 
     Liquidation Rights.  In the event of any liquidation, dissolution or
winding-up of UST whether voluntary or involuntary, the holders of UST Common
Stock are entitled to share, on a share for share basis, in any of the assets
UST legally available for distribution to such shareholders after the payment of
all debts and other liabilities of UST and any preferential amounts attributable
to any Preferred Stock that may then be outstanding.
 
     Assessments.  Outstanding shares of UST Common Stock are, and the shares of
UST Common Stock being registered hereby will be, fully paid and non-assessable.
 
     Transfer Agent and Registrar.  UST's wholly-owned subsidiary, United States
Trust Company, 30 Court Street, Boston, Massachusetts 02108, serves as transfer
agent and registrar for UST's Common Stock.
 
     Stockholder Rights Agreement.  On September 19, 1995, the UST Board adopted
the UST Rights Agreement providing for a dividend of one preferred share
purchase right for each outstanding share of UST Common Stock (the "Rights").
The dividend was distributed on October 6, 1995, to stockholders of record on
that date. Holders of shares of UST Common Stock issued subsequent to that date
receive the Rights with their shares. The Rights trade automatically with shares
of UST Common Stock and become exercisable only under certain circumstances as
described below. The Rights are designed to protect the interests of UST and its
stockholders against coercive third-party takeover tactics. The purpose of the
Rights is to encourage potential acquirers to negotiate with the UST Board prior
to attempting a takeover and to provide the UST Board with leverage in
negotiating on behalf of all stockholders the terms of any proposed takeover.
The
 
                                       73
<PAGE>   87
 
Rights may have certain anti-takeover effects. The Rights should not, however,
interfere with any merger or other business combination approved by the UST
Board.
 
     The Rights will become exercisable only if a person or group (i) acquires
15% or more of the outstanding shares of UST Common Stock, (ii) announces a
tender offer that would result in ownership of 15% or more of the outstanding
UST Common Stock, or (iii) is declared to be an "Adverse Person" by the UST
Board. An "Adverse Person" includes any person or group who owns at least 10% of
the outstanding shares of UST Common Stock and attempts an action that would
adversely impact UST. Each right would entitle a stockholder to buy 1/100th of a
share of UST's Series A Junior Participating Preferred Stock. See "DESCRIPTION
OF UST CAPITAL STOCK -- Preferred Stock."
 
     Once a person or group has acquired 15% or more of the outstanding shares
of UST Common Stock or is declared an "Adverse Person" by the UST Board, each
Right may entitle its holder (other than the acquiring person or adverse person)
to purchase, at an exercise price of $40 per share, shares of UST Common Stock
(or of any company that acquires UST) at a price equal to 50% of their current
market price. Under certain circumstances, the Continuing Directors (as defined
in the Stockholder Rights Agreement) may exchange the Rights for UST Common
Stock (or equivalent securities) on a one-for-one-basis.
 
     Until declaration of a Person as an Adverse Person, or ten days after
public announcement that any person or group has acquired 15% or more of the
outstanding shares of UST Common Stock, the Rights are redeemable at the option
of the UST Board in certain cases with the concurrence of the Continuing
Directors. Thereafter, they may be redeemed by the Continuing Directors in
connection with certain acquisitions not involving any acquiring person or
Adverse Person or in certain circumstances following a disposition of shares by
the acquiring person or Adverse Person. The redemption price is $0.001 per
Right. The Rights will expire on October 6, 2005, unless redeemed prior to that
date.
 
     The foregoing description of the Rights does not purport to be complete and
is qualified in its entirety by the description of the Rights contained in the
UST Rights Agreement, dated as of June 28, 1990, between UST and USTC, as Rights
Agent, which is incorporated herein by reference to Exhibit 1 to UST's
Registration Statement on Form 8-A dated September 26, 1995.
 
PREFERRED STOCK
 
     General.  The Preferred Stock is of a serial or "blank check" nature. Under
Chapter 156B of the Massachusetts General Laws, after stockholder authorization
of such a class of preferred stock, one or more series of preferred stock may be
established and designated by action of the UST Board with varying rights,
preferences and limitations and without further stockholder action. The UST
Board may also fix the number of shares of the series. Series are established by
the filing with the Secretary of State of The Commonwealth of Massachusetts of a
certificate which is made in part of the filing company's Articles of
Organization and which sets forth the rights, preferences and limitations of the
respective series.
 
     Dividend and Liquidation Rights.  Each series of the Preferred Stock, when
issued, would have preference over the UST Common Stock with respect to the
payment of all dividends and distribution of assets in the event of liquidation
or dissolution of UST, and may have other preferences.
 
     Determinations to be Made by the UST Board.  The determinations for each
series of Preferred Stock which would be made by the UST Board include (1) the
number of shares to constitute such series, (2) the dividend rate or rates (or
the manner of determining the same) on the shares of such series, (3) whether
dividends shall be cumulative, (4) whether the shares of the series shall be
redeemable and the terms thereof, (5) whether the shares of the series shall be
convertible into other securities of UST, including the Common Stock, and the
terms and conditions thereof, (6) the special relative rights of holders of
shares of the series in the event of liquidation, distribution or sale of
assets, dissolution or winding-up of UST, (7) the terms of voting rights, if
any, of shares of the series, (8) the title or designation of the series and (9)
such other rights and privileges and any qualifications, limitations or
restrictions of such rights or privileges of such series as may be permitted by
applicable law. As noted above, before any series would be issued, a certificate
setting
 
                                       74
<PAGE>   88
 
forth the terms thereof would be authorized by the UST Board and filed pursuant
to the MBCL but no further stockholder action would be required for the issuance
of such authorized shares.
 
     Series A Junior Participating Preferred Stock.  In connection with the UST
Rights Agreement, the UST Board established a series of Preferred Stock, par
value $1.00 per share, designated as Series A Junior Participating Preferred
Stock ("Series A"). The number of shares constituting Series A is 300,000. A
certificate was filed with the Secretary of the Commonwealth of Massachusetts on
September 29, 1995 setting forth the determinations discussed above. Holders of
Series A Preferred Stock are entitled to receive, in preference to the holders
of UST Common Stock, quarterly dividends payable in cash on the first of March,
June, September and December in each year after the first issuance of a share or
a fraction of a share of Series A Preferred Stock, in an amount per share equal
to the greater of (a) $1 or (b) subject to adjustment, 100 times the aggregate
per share amount of all cash dividends, and 100 times the aggregate per share
amount (payable in kind) of all non-cash dividends, other than a dividend
payable in UST Common Stock. Series A Preferred Stock dividends are cumulative
but do not bear interest. Shares of Series A Preferred Stock are not redeemable.
Each share of Series A Preferred Stock entitles the holder thereof to 100 votes
on all matters submitted to a vote of the UST stockholders and no other special
voting rights. Upon any liquidation, dissolution or winding up holders of Series
A Preferred Stock are entitled to priority over the holders of share of UST
Common Stock or other junior ranking stock. No such shares of Series A Preferred
Stock are issued or outstanding, however, each holder of UST Common Stock was
granted the right to purchase Series A Preferred Stock upon the happening of
certain events, such as a hostile takeover attempt of UST, as described in the
UST Rights Agreement. See "DESCRIPTION OF UST CAPITAL STOCK -- Stockholder
Rights Plan."
 
                                       75
<PAGE>   89
 
                       COMPARATIVE RIGHTS OF STOCKHOLDERS
 
GENERAL
 
     Upon consummation of the transactions contemplated in the Affiliation
Agreement, the stockholders of Walden who do not perfect and exercise their
statutory dissenters' rights will become stockholders of UST. Since both UST and
Walden are Massachusetts corporations, Walden stockholders who receive UST
Common Stock will continue to be subject to the privileges and restrictions set
forth in the MBCL. In addition, the rights of such stockholders as stockholders
of UST will be governed by the Articles and By-laws of UST, which differ in
certain respects from Walden's Articles and By-laws. This summary contains a
list of differences but is not meant to be relied upon as an exhaustive list or
a detailed description of the provisions discussed. This summary is qualified in
its entirety by reference to the Massachusetts General Laws, the MBCL, the UST
Rights Agreement and the Articles and By-laws of each of UST and Walden. See
"AVAILABLE INFORMATION."
 
SIZE AND CLASSIFICATION OF THE BOARD OF DIRECTORS
 
     Consistent with the MBCL, each of the UST Board and the Walden Board is
divided into three classes and the directors of each class are elected by the
stockholders to serve staggered three-year terms. The UST By-laws provide that
the UST Board be composed of not less than three nor more the twenty-four.
Presently there are twenty directors on the UST Board and eight directors on the
Walden Board.
 
REMOVAL OF DIRECTORS
 
     Notwithstanding contrary provisions in the UST By-laws and the Walden
Articles, pursuant to the MBCL, directors on the UST Board and the Walden Board,
respectively, may be removed by the affirmative vote of a majority of the
holders of the shares outstanding and entitled to vote in the election of UST
and Walden Directors, respectively only for "cause" as defined in the MBCL.
 
STOCKHOLDER NOMINATIONS
 
     UST.  The UST Articles and the UST By-laws do not set forth procedures
regarding stockholder nominations of individuals for election to the UST Board.
 
     Walden.  The Walden Articles set forth procedures that must be followed for
stockholders to nominate individuals for election to the Walden Board.
Nominations by stockholders entitled to vote generally in the election of
directors must be made in writing, delivered or mailed by first class United
States mail, postage prepaid, to the Clerk of Walden not less than 30 days nor
more than 60 days prior to any meeting at with directors are to be elected. Each
such notice must include (i) the name, age, business address and, if known, the
residence address of each nominee proposed in the notice, (ii) the principal
occupation in employment of each such nominee, and (iii) the number of shares of
stock of Walden beneficially owned by each nominee.
 
INTERESTED TRANSACTIONS
 
     UST.  None of the MBCL, UST Articles or the UST By-laws has a general
provision governing interested transactions. Therefore, transactions between UST
and any of its directors, officers or security holders or between UST and any
entity in which any director, officer or security holder of UST is financially
interested is governed by the decisional law set down by the Massachusetts
Courts. Interested transactions are not per se voidable but may be challenged on
the grounds that such a transaction was not entered into in good faith or was
unfair to the corporation. In determining good faith and fairness, courts will
consider whether a full and honest disclosure of all relevant circumstances of
the transaction had been disclosed as well as whether approval of disinterested
stockholders had been obtained. The determination of good faith and fairness is
particular to the facts and circumstances of each case.
 
     Walden.  Under the Walden Articles, no contract or transaction between
Walden, and any of its directors, officers or security holders, or between
Walden and any entity in which a director, officer or security holder is,
directly or indirectly, financially interested will be void or voidable solely
because of this relationship,
 
                                       76
<PAGE>   90
 
or solely because of the presence of the interested party at the meeting
authorizing the transaction or contract, or solely because of his or their
participation in the authorization of the transaction or contract or vote at the
meeting for authorization, whether or not such participation in the vote was
necessary for such authorization provided that, (a) the material facts as to the
relationship or interest and as to the contract or transaction are disclosed or
are known to the Walden Board (or committee thereof) and the Walden Board,
nevertheless in good faith authorized or ratifies the contract or transaction by
a majority of the directors present, counting each interested director for
quorum purposes but not for calculating the majority necessary for approval, and
(b) the contract or transaction is fair to Walden as of the time it was
authorized or ratified by the Walden Board (or committee thereof) or the
stockholders.
 
MEETINGS OF STOCKHOLDERS
 
     UST.  The By-laws of UST provide that special meetings of stockholders may
be called by the President or by the UST Board or, upon written application of
one or more stockholders who hold at least 10% of the capital stock entitled to
vote at the meeting, by the Clerk, or in the case of the death, absence
incapacity or refusal of the Clerk, by any other officer.
 
     Walden.  Under the Articles of Organization of Walden, special meetings of
stockholders may be called at any time by the Walden Board, the president, the
chairman of the board or by a committee of the Walden Board which has been duly
authorized by the Walden Board or the by-laws to do so. No other person may call
a special meeting.
 
STOCKHOLDER ACTION WITHOUT A MEETING
 
     UST.  As authorized by the MBCL, the UST By-laws provide that any action to
be taken by UST stockholders may be taken without a meeting if all stockholders
entitled to vote on the matter consent to the action by a writing filed with the
records of the meetings of the stockholders.
 
     Walden.  The Walden Articles specifically deny the power of stockholders to
consent in writing, without a meeting, to the taking of any action required to
be taken or which may be taken at any annual or special meeting of the
stockholders of Walden.
 
AMENDMENT OF BY-LAWS
 
     UST.  The UST By-laws may at any time be amended by a vote of the
stockholders, provided that notice of the substance of the proposed amendment is
stated in the notice of the meeting.
 
     Walden.  Unlike the UST Articles, the Walden Articles specifically
authorize the Walden Board to make, repeal, alter, amend and rescind the Walden
by-laws by a vote of two-thirds of the directors then in office. No by-law of
Walden may be made, repealed, altered, amended or repealed by the Walden
stockholders except by a vote of the holders of not less than two-thirds of the
outstanding shares of capital stock of Walden entitled to vote on the election
of Directors cast at a meeting of the stockholders called for the purpose
(provided that notice of such proposed adoption, repeal, alteration, amendment
or recession is included in the notice of such meeting).
 
REQUIRED VOTE FOR CERTAIN BUSINESS COMBINATIONS
 
     UST.  The MBCL provides that an agreement of merger or consolidation, or a
sale, lease or exchange of all or substantially all of the property and assets
of a corporation must be approved by the holders of two-thirds of the shares of
each class of stock outstanding and entitled to vote thereon, unless a
corporation's articles of organization designate a lower percentage (but not
less than a majority). The UST Articles and the UST By-laws do not contain
provisions that require a specific lower or higher stockholder vote for such
transactions.
 
                                       77
<PAGE>   91
 
     Walden.  In addition to the affirmative vote required by the MBCL, the
Walden Articles provide that the affirmative vote of either a majority of the
continuing Directors (as defined in the provision) or of the holders of at least
two-thirds of the outstanding shares entitled to vote thereon is required to
authorize any reclassification of the Walden Common Stock or any
recapitalization involving the Walden Common Stock, or any combination or other
transactions with a stockholder who beneficially owns 10% or more of the
outstanding Walden Common Stock (a "Related Person") or with an affiliate of a
Related Person unless:
 
          (a) the aggregate amount of cash and Fair Market Value (as defined in
     the provision) of consideration other than cash to be received by holders
     of Walden Common Stock is at least equal to the highest of (i) the highest
     price per share paid by the Related Person in acquiring any share of Walden
     Common Stock within the two-year period immediately prior to the first
     public announcement of the proposal of the business combination (the
     "Announcement Date"), or in the transaction in which it became a Related
     Person, whichever is higher; (ii) the Fair Market value per share of Walden
     Common Stock on the Announcement Date or on the date on which the Related
     Person became a Related Person (the "Determination Date"), whichever is
     higher, or (iii) the price per share equal to the Fair Market Value per
     share of Walden Common Stock determined by the preceding clause (a)(ii),
     multiplied by a ratio of (x) the highest per share price paid by the
     Related Person for any shares of Walden Common Stock acquired within the
     two-year period immediately prior to the Announcement Date to (y) the Fair
     Market Value per share of Walden Common Stock on the first day in such
     two-year period on which the Related Person acquired any shares of Walden
     Common Stock;
 
          (b) the aggregate amount of cash and Fair Market Value of
     consideration other than cash to be received by holders of shares of any
     class of outstanding voting stock other then Walden Common Stock is at
     least equal to the highest of (i) the highest price per share paid by the
     Related Person in acquiring any share of such voting stock acquired by it
     within the two-year period immediately prior to the Announcement Date or in
     the transaction in which it became a Related Person, whichever is higher,
     (ii) the highest preferential amount per share to which holders of shares
     of such class of voting stock would be entitled in the event of any
     voluntary or involuntary liquidation, dissolution or winding up of the
     affairs of Walden, even if the business combination to be consummated does
     not constitute such an event, (iii) the Fair Market Value per share of such
     class of voting stock on the Announcement Date or the Determination Date,
     whichever is higher, or (iv) the price per share equal to the Fair Market
     Value per share of such class of voting stock determined by the preceding
     clause (b)(iii) multiplied by a ration of (x) the highest per share price
     paid by the Related Person for any share of such voting stock acquired
     within the two-year period immediately prior to the Announcement Date to
     (y) the Fair Market Value per share of such voting stock on the first day
     in such two-year period upon which the Related Person acquired any shares
     of such class of voting stock; and
 
          (c) certain procedural requirements were satisfied including the
     requirement that the considerations to be paid to Walden's stockholders
     must be in cash or the same type of consideration previously used by the
     Related Person to acquire the largest number of shares of such class of
     voting stock previously acquired.
 
     The Walden Board has determined that the requirements described in
paragraphs (a) through (c) above do not apply to the Affiliation Agreement, the
Plan of Merger and the transactions contemplated thereby.
 
STOCKHOLDER RIGHTS PLAN
 
     UST.  UST has distributed to each holder of UST Common Stock one Right per
each outstanding share of UST Common Stock. In addition, a Right is distributed
with each newly issued share of UST Common Stock. Holders of Walden Common Stock
will receive one Right with each share of UST Common Stock upon the conversion
of their shares of Walden Common Stock at the Effective Time. Each Right
entitles the holder thereof to purchase one share of preferred stock in the
event of certain transactions involving UST. See "DESCRIPTION OF UST CAPITAL
STOCK -- Common Stock -- Stockholder Rights Plan."
 
     Walden.  Walden has no stockholder rights plan.
 
                                       78
<PAGE>   92
 
STATE ANTI-TAKEOVER STATUTES
 
     The Massachusetts General Laws prohibit corporations from engaging in a
"business combination" with an "interested stockholder" for a period of three
years after the date of the transaction in which the person becomes an
interested stockholder, unless: (a) the interested stockholder obtains the
approval of the board of directors prior to becoming an interested stockholder,
or (b) the interested stockholder acquires 90% of the outstanding voting stock
of the corporation (excluding shares held by certain affiliates of the
corporation) at the time that he becomes an interested Stockholder, or (c) the
business combination is approved by both the board of directors and two-thirds
of the outstanding voting stock of the corporation (excluding shares held by the
interested stockholder). An "interested stockholder" is a person who, together
with affiliates and associates, owns (or at any time with the prior three years
did own) 5% or more of a corporation's voting stock. A "business combination"
includes mergers, stock and asset sales and other transactions resulting in a
financial benefit to the stockholders. The business combinations statute does
not apply to the Affiliation Agreement, the Plan of Merger, the Stock Option
Agreement or any of the transactions contemplated by such agreements, because
the UST Board and the Walden Board each had approved the Affiliation Agreement,
the Plan of Merger and the Stock Option Agreement prior to their execution.
 
     The Massachusetts General Laws include a statute concerning "control share
acquisitions," which limits the voting rights of shares held by persons who have
acquired a certain percentage of the voting power of a corporation. Under the
Massachusetts statute, shares acquired in a control share acquisition retain the
same voting rights as all other shares of the same class or series but only to
the extent authorized by a vote of the majority of all shares entitled to vote
for the election of directors (such acquired shares not being entitled to vote).
 
                          MARKET PRICES AND DIVIDENDS
 
     General.  Transactions with respect to UST Common Stock and Walden Common
Stock are quoted on the NASDAQ National Market under the Symbols "USTB" and
"WLDN," respectively. The following tables set forth the high and low sales
prices for each of UST Common Stock and Walden Common Stock as quoted by NASDAQ
and dividends declared for the periods indicated. The stock prices for Walden
listed below for the periods prior to December 8, 1995 are those of Concord
because it is considered to be the predecessor institution of Walden for
historical reporting purposes by NASDAQ.
 
<TABLE>
<CAPTION>
                                                  UST                                WALDEN
                                    --------------------------------     -------------------------------
                                                            DIVIDEND                            DIVIDEND
                                      LOW        HIGH       DECLARED       LOW        HIGH      DECLARED
                                    -------     -------     --------     -------     ------     --------
<S>                                 <C>         <C>         <C>          <C>         <C>        <C>
1994
  First Quarter...................  $ 10.50     $ 13.50          --      $ 14.75     $20.50      $ 0.05
  Second Quarter..................    12.625      14.375         --        16.50      21.25        0.08
  Third Quarter...................    11.25       13.50          --        16.50      19.75        0.08
  Fourth Quarter..................     8.75       11.75          --        12.50      17.25        0.10
1995
  First Quarter...................     9.75       11.375         --        13.00      17.25        0.10
  Second Quarter..................    10.50       13.50          --        14.50      20.50        0.12
  Third Quarter...................    13.25       15.00          --        15.625     19.50        0.12
  Fourth Quarter..................    12.75       15.50        0.05        16.75      20.00        0.14
1996
  First Quarter...................    13.00       15.125       0.06        18.00      20.00        0.14
  Second Quarter..................    12.75       15.125       0.07        18.50      20.50        0.16
  Third Quarter...................    14.25       17.125       0.08        18.50      31.00        0.16
</TABLE>
 
                                    EXPERTS
 
     The consolidated financial statements of UST appearing in UST's Annual
Report on Form 10-K for the year ended December 31, 1995, have been audited by
Arthur Andersen LLP, independent public accountants, as indicated in their
reports with respect thereto, and are included therein and incorporated herein
by reference. Such consolidated financial statements are incorporated in
reliance upon the authority of such firm as experts in accounting and auditing
in giving said report.
 
                                       79
<PAGE>   93
 
     The consolidated financial statements of Walden as of December 31, 1995
have been audited by Arthur Andersen LLP, independent public accountants, as
indicated in their report with respect thereto, and those consolidated financial
statements and the reports of Arthur Andersen LLP with respect to those
consolidated financial statements and the consolidated financial statements of
The Bank of Braintree as of December 31, 1994 and 1993 are incorporated by
reference herein in reliance upon the authority of said firm as experts in
accounting and auditing in giving said reports.
 
     The report of KPMG Peat Marwick LLP with respect to the consolidated
financial statements of The Co-operative Bank of Concord as of December 31, 1994
and 1993 is incorporated by reference herein in reliance upon the authority of
said firm as experts in accounting and auditing in giving said report.
 
                                 LEGAL OPINIONS
 
     The validity of the UST Common Stock offered hereby will be passed upon for
UST by Eric R. Fischer, General Counsel. As of October 1, 1996, Mr. Fischer had
a direct or indirect interest in 37,371 shares of UST Common Stock and had
options to purchase an additional 40,800 shares, all of which options were
immediately exercisable.
 
     The Affiliation Agreement provides as a condition to UST and Walden's
obligation to consummate the Affiliation that UST receive a tax opinion, dated
as of the date of the closing of the Affiliation, from its counsel, Bingham,
Dana & Gould LLP, and Walden receive a tax opinion, dated as of the date of this
Joint-Proxy Statement-Prospectus and as of the date of the closing of the
Affiliation, from its tax advisor Arthur Andersen LLP (or from another tax
advisor acceptable to UST and Walden) substantially to the effect that, among
other things, the Affiliation will be treated as a reorganization as described
in Section 368 of the Code. As required by the Affiliation Agreement, Arthur
Andersen LLP has delivered such an opinion to Walden dated as of the date of
this Joint Proxy Statement - Prospectus. See "THE AFFILIATION -- Certain Federal
Income Tax Consequences."
 
                     MANAGEMENT AND ADDITIONAL INFORMATION
 
     Certain information relating to the executive compensation, various benefit
plans (including stock option plans), voting securities and the principal
holders thereof, certain relationships and related transactions and other
related matters as to UST and Walden is incorporated by reference or set forth
in UST's Annual Report on Form 10-K for the year ended December 31, 1995 and
Walden's Annual Report on Form 10-K for the year ended December 31, 1995, each
of which is incorporated herein by reference. See "INCORPORATION OF CERTAIN
INFORMATION BY REFERENCE." Stockholders of Walden desiring copies of such
documents may contact UST or Walden, as the case may be, at its address or phone
number indicated under "INCORPORATION OF CERTAIN INFORMATION BY REFERENCE." For
certain information regarding the directors and certain executive officers of
Walden after the effective time of the Affiliation, see "THE AFFILIATION --
Management and Operations After the Affiliation," "-- Interests of Certain
Persons in the Affiliation" and "-- Employee Matters."
 
                            SOLICITATION OF PROXIES
 
     Walden and UST will each bear their own expenses incurred in connection
with the solicitation of proxies from holders of UST Common Stock and Walden
Common Stock, including the cost of reimbursing brokerage houses and other
Custodians, nominees or fiduciaries for forwarding proxies and proxy statements
to their principals; however, pursuant to the Affiliation Agreement, the expense
of printing and distributing the Registration Statement and this Joint Proxy
Statement - Prospectus will be shared equally by Walden and UST. In addition to
solicitation of proxies by mail, proxies may also be solicited by telephone or
personal interview by certain directors, officers and regular employees of UST
and Walden and its subsidiaries, who will not receive additional compensation
therefor. UST has retained Morrow & Company to assist in the distribution and
solicitation of proxies, at a fee of approximately $6,000 plus reasonable out of
pocket expenses. Walden has retained Morrow & Company to assist in the
distribution and solicitation of proxies, at a fee of approximately $6,000, plus
reasonable out-of-pocket expenses. UST and Walden will also reimburse brokerage
firms and others who hold record ownership for third parties for their expenses
in forwarding proxy materials to the beneficial owners of UST Common Stock and
Walden Common Stock.
 
                                       80
<PAGE>   94
 
                              [ALTERNATE UST PAGE]
 
                     THE UST MEETING -- ADDITIONAL MATTERS
 
                    INCREASE IN NUMBER OF AUTHORIZED SHARES
                              OF UST COMMON STOCK
 
                                 (Proxy Item 2)
 
     The UST Board has adopted a vote recommending that stockholders amend the
UST Articles to increase the authorized shares of UST Common Stock from
30,000,000 shares to 45,000,000.
 
     On the Record Date, the number of shares of UST Common Stock issued or
reserved for issuance totaled approximately 19,269,430. UST expects to issue
approximately 10,611,549 shares of UST Common Stock to holders of Walden Common
Stock in the Affiliation. Thus out of the 30,000,000 shares currently
authorized, UST would have only approximately 119,021 shares of UST Common Stock
available for future issuance following the Affiliation.
 
     The increase in authorized shares, in the opinion of the UST Board, is
desirable to provide UST with the ability to meet future business needs and
opportunities, including the ability to exercise, if it is deemed appropriate to
do so, its option to increase the consideration to be received by the holders of
Walden Common Stock in the Affiliation by adjusting the Conversion Number in
order to prevent a termination of the Affiliation Agreement by Walden in the
event that the value of UST Common Stock declines in an amount greater than the
formula set forth in the Affiliation Agreement. The increased number of
authorized shares will be available for issuance from time to time, without
further action or authorization by the stockholders (except as required under
applicable law or by an applicable national stock exchange or market), in
connection with potential investment opportunities, acquisitions of other
companies or for other corporate purposes as determined by the UST Board. These
other purposes might include raising additional capital funds through offerings
of shares of UST Common Stock, the issuance of shares of UST Common Stock in
connection with the declaration of stock dividends, and the issuance of shares
in connection with employee benefit plans and incentive compensation plans of
UST and its subsidiaries.
 
     If such additional authorized shares are issued to persons other than
existing stockholders, the percentage interest of existing stockholders in UST
will be reduced. Although the existence or issuance of authorized but unissued
shares of UST capital stock could, under certain circumstances, have an
anti-takeover effect, UST has no present intention of issuing such shares for
anti-takeover purposes.
 
     If the amendment is approved, as soon as practicable after the UST Meeting,
UST will file with the Massachusetts Secretary of State's Office, Articles of
Amendment to the UST Articles reflecting the increase in authorized shares.
 
     Approval of this proposal requires the affirmative vote of the holders of
at least a majority of the outstanding shares of UST Common Stock.
 
     THE UST BOARD RECOMMENDS THAT YOU VOTE FOR THE PROPOSAL TO AMEND THE UST
ARTICLES TO PROVIDE FOR AN INCREASE IN THE NUMBER OF AUTHORIZED SHARES OF UST
COMMON STOCK.
 
                                       81
<PAGE>   95
 
                              [ALTERNATE UST PAGE]
 
                           PROPOSALS OF STOCKHOLDERS
 
     Any stockholder of UST desiring to submit proposals pursuant to Rule 14a-8
under the Exchange Act for action at the 1997 Annual Meeting of UST, must have
delivered such proposal to the main office of UST no later than December 26,
1996, for it to be included in UST's proxy statement and form of proxy relating
to that meeting. Stockholders submitting a proposal must meet the requirements
specified in Rule 14a-8 under the Exchange Act.
 
                                            By Order of the Board of Directors
 
                                            /s/ Eric R. Fischer
                                            ERIC R. FISCHER, Executive Vice
                                            President, General Counsel and
                                            Clerk
 
                                       82
<PAGE>   96
 
                            [ALTERNATE WALDEN PAGE]
 
                           PROPOSALS OF STOCKHOLDERS
 
     Walden will hold an Annual Meeting in 1997 only if the Affiliation is not
consummated before the time of such meeting. If necessary, the Annual Meeting is
expected to be held on April 30, 1997.
 
     Any stockholder of Walden desiring to present a proposal for action at the
1997 Annual Meeting of Walden, in the event that such a meeting is held, must
have delivered such proposal to the main office of Walden no later than November
21, 1996, for it to be included in Walden's proxy statement and form of proxy
relating to that meeting. Stockholders submitting a proposal must meet the
requirements specified in Rule 14a-8 under the Exchange Act.
 
                                            By Order of the Board of Directors
 
 
                                            /s/ JOSIAH S. CUSHING, II
                                                Clerk
 
                                       81
<PAGE>   97
                                                                      APPENDIX A
                                                                      ----------


================================================================================


                            AFFILIATION AGREEMENT AND
                             PLAN OF REORGANIZATION



                           DATED AS OF AUGUST 30, 1996

                                     BETWEEN

                                    UST CORP.

                                       AND

                              WALDEN BANCORP, INC.




================================================================================

<PAGE>   98


                                TABLE OF CONTENTS

                                                                          Page
                                                                          ----

ARTICLE I      DEFINITIONS  ............................................   A-1

ARTICLE II     THE MERGER  .............................................   A-5

ARTICLE III    REPRESENTATIONS AND WARRANTIES OF THE BUYER  ............   A-6

  [Section]3.01  Corporate Organization  ...............................   A-6
  [Section]3.02  Capitalization  .......................................   A-6
  [Section]3.03  Authority; No Violation  ..............................   A-7
  [Section]3.04  Consents and Approvals  ...............................   A-8
  [Section]3.05  Financial Statements  .................................   A-9
  [Section]3.06  Absence of Undisclosed Liabilities  ...................   A-9
  [Section]3.07  Broker's Fees  ........................................   A-9
  [Section]3.08  Absence of Certain Changes or Events  .................   A-9
  [Section]3.09  Legal Proceedings  ....................................  A-10
  [Section]3.10  Reports  ..............................................  A-10
  [Section]3.11  Buyer Common Stock  ...................................  A-10
  [Section]3.12  Ownership of Seller Common Stock  .....................  A-10
  [Section]3.13  Taxes and Tax Returns  ................................  A-10
  [Section]3.14  Employees  ............................................  A-11
  [Section]3.15  Agreements with Banking Authorities  ..................  A-12
  [Section]3.16  Compliance with Applicable Law  .......................  A-12
  [Section]3.17  Capitalization  .......................................  A-12
  [Section]3.18  CRA Rating  ...........................................  A-12
  [Section]3.19  Buyer Information  ....................................  A-12
  [Section]3.20  Disclosure  ...........................................  A-12

ARTICLE IV     REPRESENTATIONS AND WARRANTIES OF THE SELLER  ...........  A-13

  [Section]4.01  Corporate Organization  ...............................  A-13
  [Section]4.02  Capitalization  .......................................  A-13
  [Section]4.03  Authority; No Violation  ..............................  A-14
  [Section]4.04  Consents and Approvals  ...............................  A-15
  [Section]4.05  Financial Statements  .................................  A-16
  [Section]4.06  Absence of Undisclosed Liabilities  ...................  A-16
  [Section]4.07  Broker's Fees  ........................................  A-16
  [Section]4.08  Absence of Certain Changes or Events  .................  A-16
  [Section]4.09  Legal Proceedings  ....................................  A-16
  [Section]4.10  Taxes and Tax Returns  ................................  A-17
  [Section]4.11  Employees  ............................................  A-17
  [Section]4.12  Agreements with Banking Authorities  ..................  A-18
  [Section]4.13  Material Agreements  ..................................  A-19
  [Section]4.14  Ownership of Property  ................................  A-19
  [Section]4.15  Reports  ..............................................  A-20
  [Section]4.16  Compliance with Applicable Law  .......................  A-20
  [Section]4.17  Environmental Matters  ................................  A-20
  [Section]4.18  Chapters 110D and 110F Not Applicable  ................  A-22
  [Section]4.19  Ownership of Buyer Common Stock  ......................  A-22
  [Section]4.20  Insurance  ............................................  A-22
  [Section]4.21  Labor  ................................................  A-22
  [Section]4.22  Material Interests of Certain Persons  ................  A-22

                                      A-i
<PAGE>   99

  [Section]4.23  Absence of Registration Obligations  ..................  A-23
  [Section]4.24  Loans  ................................................  A-23
  [Section]4.25  Capitalization  .......................................  A-23
  [Section]4.26  CRA Rating  ...........................................  A-23
  [Section]4.27  Seller Information  ...................................  A-23
  [Section]4.28  Disclosure  ...........................................  A-23

ARTICLE V      COVENANTS OF THE PARTIES  ...............................  A-24

  [Section]5.01  Conduct of the Business of Seller  ....................  A-24
  [Section]5.02  Access to Properties and Records; Confidentiality  ....  A-27
  [Section]5.03  No Solicitation  ......................................  A-28
  [Section]5.04  Regulatory Matters; Consents  .........................  A-29
  [Section]5.05  Approval of Stockholders  .............................  A-30
  [Section]5.06  Agreements of Affiliates; Publication of Combined
                  Financial Results  ...................................  A-30
  [Section]5.07  Further Assurances  ...................................  A-31
  [Section]5.08  Public Announcements  .................................  A-31
  [Section]5.09  Post-Closing Governance  ..............................  A-31
  [Section]5.10  Merger Subsidiary  ....................................  A-31
  [Section]5.11  Tax-Free Reorganization Treatment; Accounting  ........  A-32
  [Section]5.12  Stock Listing  ........................................  A-32
  [Section]5.13  Employment and Benefit Matters  .......................  A-32
  [Section]5.14  Accountants' Letters  .................................  A-32
  [Section]5.15  Directors' and Officers' Indemnification and Insurance   A-33
  [Section]5.16  Conversion of Seller Stock Options  ...................  A-33
  [Section]5.17  Maintenance of Records  ...............................  A-33
  [Section]5.18  Leases  ...............................................  A-33
  [Section]5.19  Dividends  ............................................  A-39
  [Section]5.20  Notice of Change  .....................................  A-43
  [Section]5.21  Changes in Accounting  ................................  A-34
  [Section]5.22  SEC Filings  ..........................................  A-34
  [Section]5.23  Covenants of Buyer  ...................................  A-34
  [Section]5.24  Regulatory Reports  ...................................  A-34
  [Section]5.25  Registration of Shares  ...............................  A-34
  [Section]5.26  Environmental Remediation  ............................  A-34
  [Section]5.27  Bank Mergers  .........................................  A-35

ARTICLE VI     CLOSING CONDITIONS  .....................................  A-35

  [Section]6.01  Conditions to Each Party's Obligations Under This
                   Agreement  ..........................................  A-35
  [Section]6.02  Conditions to the Obligations of the Buyer Under This
                   Agreement  ..........................................  A-35
  [Section]6.03  Conditions to the Obligations of the Seller Under This
                   Agreement  ..........................................  A-37

ARTICLE VII    CLOSING  ................................................  A-38

  [Section]7.01  Time and Place  .......................................  A-38
  [Section]7.02  Deliveries at the Closing  ............................  A-38

                                      A-ii
<PAGE>   100
ARTICLE VIII   TERMINATION, AMENDMENT AND WAIVER........................  A-38

  [Section]8.01  Termination  ..........................................  A-38
  [Section]8.02  Effect of Termination  ................................  A-40
  [Section]8.03  Amendment, Extension and Waiver  ......................  A-40

ARTICLE IX     MISCELLANEOUS  ..........................................  A-41

  [Section]9.01  Expenses  .............................................  A-41
  [Section]9.02  Survival  .............................................  A-41
  [Section]9.03  Notices  ..............................................  A-41
  [Section]9.04  Parties in Interest  ..................................  A-42
  [Section]9.05  Complete Agreement  ...................................  A-42
  [Section]9.06  Counterparts  .........................................  A-42
  [Section]9.07  Governing Law  ........................................  A-42
  [Section]9.08  Captions  .............................................  A-42
  [Section]9.09  Effect of Investigations  .............................  A-42
  [Section]9.10  Severability  .........................................  A-43
  [Section]9.11  Specific Enforceability  ..............................  A-43

                             EXHIBITS AND SCHEDULES

EXHIBITS
- --------


Exhibit A      Agreement and Plan of Merger (See Appendix B)
Exhibit B-1    Buyer Affiliates Agreement
Exhibit B-2    Seller Affiliates Agreement
Exhibit C      Seller Option Agreement
Exhibit D      Stockholder Agreement
Exhibit E      List of Index Companyies with Weighted Averages

SCHEDULES
- ---------

Buyer Disclosure Schedule (omitted)
Seller Disclosure Schedule (omitted)

                                     A-iii

<PAGE>   101


                AFFILIATION AGREEMENT AND PLAN OF REORGANIZATION

     AFFILIATION AGREEMENT AND PLAN OF REORGANIZATION (the "AGREEMENT"), dated
as of August 30, 1996, between UST CORP., a Massachusetts corporation (the
"BUYER"), and WALDEN BANCORP, INC., a Massachusetts corporation (the "SELLER").

     The Boards of Directors of the Buyer and the Seller deem it advisable and
in the best interests of their respective stockholders to consummate, and have
approved, the business combination transactions provided for herein.

     In consideration of the mutual covenants, representations, warranties and
agreements contained herein and in consideration of the Seller Option Agreement
(as hereinafter defined), pursuant to which the Seller has on this day granted
the Seller Option (as hereinafter defined) and in consideration of the execution
and delivery of the Stockholder Agreement to the Buyer, the parties agree as
follows:

                                    ARTICLE I

                                   DEFINITIONS
                                   -----------

     Except as otherwise provided herein or as otherwise clearly required by the
context, the following terms shall have the respective meanings indicated when
used in this Agreement:

     "AMEX" shall mean the American Stock Exchange.

     "ACQUISITION TRANSACTION" shall have the meaning ascribed thereto in
Section 5.03 hereof.

     "AGREEMENT" shall mean this Affiliation Agreement and Plan of
Reorganization by and between the Buyer and the Seller.

     "BHCA" shall mean the Bank Holding Company Act of 1956, as amended.

     "BUYER" shall have the meaning ascribed thereto in the introductory
paragraph hereof.

     "BUYER AFFILIATEs" shall have the meaning ascribed thereto in Section
5.06(b) hereof.

     "BUYER AFFILIATES AGREEMENT" shall mean the form of written agreement to be
executed and delivered to the Seller prior to the Effective Time by the Buyer
Affiliates, substantially in the form attached hereto as Exhibit B-1.

     "BUYER BALANCE SHEET" shall have the meaning ascribed thereto in Section
3.05 hereof.

     "BUYER COMMON STOCK" shall have the meaning ascribed thereto in Section
3.02(a) hereof.

     "BUYER COMPANIES" shall have the meaning ascribed thereto in Section
3.13(a) hereof.

     "BUYER DISCLOSURE SCHEDULE" shall have the meaning ascribed thereto in
Section 3.01(b) hereof.

     "BUYER PENSION PLANS" shall have the meaning ascribed thereto in Section
3.14(a) hereof.

     "BUYER PREFERRED STOCK" shall have the meaning ascribed thereto in Section
3.02(a) hereof.

<PAGE>   102


     "BUYER REPORTS" shall have the meaning ascribed thereto in Section 3.10
hereof.

     "BUYER RIGHTS AGREEMENT" shall mean that certain Rights Agreement which was
adopted by the Buyer on September 19, 1995.

     "CLOSING" shall mean the consummation of the Merger.

     "CLOSING DATE" shall mean the time and date specified pursuant to Section
7.01 hereof as the time and date on which the parties hereto shall consummate
the Merger.

     "CMPs" has the meaning ascribed to such term in Section 4.16 hereof.

     "CODE" shall mean the Internal Revenue Code of 1986, as amended.

     "COMPANIES" shall have the meaning ascribed thereto in Section 4.10(a)
hereof.

     "CONFIDENTIAL INFORMATION" shall have the meaning ascribed thereto in
Section 5.02(b) hereof.

     "CONFIDENTIALITY AGREEMENT" shall mean that certain letter agreement
between the Buyer and the Seller dated August 7, 1996.

     "CONSENTS" shall have the meaning ascribed thereto in Section 6.01(b)
hereof.

     "DISCLOSURE SCHEDULES" shall mean the Buyer Disclosure Schedule and the
Seller Disclosure Schedule, considered together.

     "D&O INSURANCE" shall have the meaning ascribed thereto in Section 5.15
hereof.

     "DOJ" shall mean the United States Department of Justice.

     "EFFECTIVE TIME" shall mean the date and time at which the Merger has
become effective pursuant to the applicable laws of The Commonwealth of
Massachusetts.

     "EPA" shall mean the United States Environmental Protection Agency.

     "EQUITY INVESTMENT" shall have the meaning set forth for such term as of
the date hereof in the FDIC's rules and regulations regarding activities and
investments of insured state banks at 12 C.F.R. [Section]362.2(k).

     "ERISA" shall mean the Employee Retirement Income Security Act of 1974, as
amended.

     "EXCHANGE ACT" shall have the meaning ascribed thereto in Section 3.05
hereof.

     "FDIA" shall mean the Federal Deposit Insurance Act, as amended.

     "FDIC" shall mean the Federal Deposit Insurance Corporation.

     "FEDERAL RESERVE BOARD" shall mean the Board of Governors of the Federal
Reserve System or the Federal Reserve Bank of Boston, as applicable.

     "FILED TAX RETURNS" shall mean, with respect to the Buyer Companies or the
Seller Companies, all Tax Returns that were required to be filed by any member
of such group of Companies on or prior to the date hereof.

                                      A-2
<PAGE>   103

     "GAAP" shall mean generally accepted accounting principles and practices in
effect from time to time within the United States applied consistently
throughout the period involved.

     "HAZARDOUS MATERIAL" shall have the meaning ascribed to such term in
Section 4.17(i) hereof.

     "INJUNCTION" shall have the meaning ascribed thereto in Section 6.01(d)
hereof.

     "JOINT PROXY STATEMENT" shall have the meaning ascribed thereto in Section
5.04(a) hereof.

     "IRS" shall mean the United States Internal Revenue Service.

     "LOAN PROPERTY" shall have the meaning ascribed thereto in Section 4.17(i)
hereof.

     "MBCL" shall mean the Massachusetts Business Corporation Law.

     "MASSACHUSETTS BOARD" shall have the meaning ascribed thereto in Section
3.04 hereof.

     "MATERIAL ADVERSE EFFECT" shall mean, with respect to any Person, a
material adverse effect on the business, results of operations or financial
condition of such Person taken as a whole; PROVIDED THAT "Material Adverse
Effect" shall not be deemed to include the impact of (a) changes in laws and
regulations or interpretations thereof by courts or governmental authorities
(including changes in insurance deposit assessment rates and special assessments
with respect thereto), (b) changes in GAAP or regulatory accounting principles
generally applicable to financial institutions and their holding companies, (c)
actions and omissions of a party (or any of its Subsidiaries) taken with the
prior written consent of the other party, (d) changes in economic conditions
(including changes in the level of interest rates) generally affecting financial
institutions, and (e) the direct effects of compliance with this Agreement on
the operating performance of the parties including expenses incurred by the
parties hereto in consummating the transactions contemplated by this Agreement
and the expenses associated with the termination of the Seller Benefit Plans as
and to the extent contemplated herein.

     "MERGER" shall have the meaning ascribed thereto in Article II hereof.

     "Merger Subsidiary" shall mean that certain business corporation that has
been or shall be organized as a wholly-owned subsidiary of the Buyer under the
laws of The Commonwealth of Massachusetts for the purpose of merging with and
into the Seller pursuant to the terms of the Plan of Merger.

     "NASD" shall mean the National Association of Securities Dealers, Inc.

     "NASDAQ" shall mean the National Association of Securities Dealers
Automated Quotation system.

     "NYSE" shall mean the New York Stock Exchange.

     "PBGC" shall mean the Pension Benefit Guaranty Corporation.

     "PARTICIPATION FACILITY" shall have the meaning ascribed to such term in
Section 4.17(i) hereof.

     "PERSON" shall mean any individual, corporation, partnership, joint
venture, association, trust, unincorporated organization or other legal entity,
or any governmental agency or political subdivision thereof.

                                      A-3
<PAGE>   104
     "PLAN OF MERGER" shall mean that certain Agreement and Plan of Merger to be
entered into by and among the Buyer, the Seller and the Merger Subsidiary at or
prior to the Effective Time, substantially in the form attached hereto as
EXHIBIT A.

     "PUBLIC ANNOUNCEMENT" shall mean a written press release, public
announcement or public information disclosure by the Seller or the Buyer or any
of their subsidiaries relating to the Merger or the other transactions
contemplated hereby.

     "RECORDS" means all records and original documents in the Seller's
possession which pertain to and are utilized by the Seller or any of its
Significant Subsidiaries to administer, reflect, monitor, evidence or record
information respecting its business and operations, including but not limited to
all records and documents relating to (a) corporate, regulatory, supervisory and
litigation matters, (b) tax planning and payment of taxes, (c) personnel and
employment matters, and (d) the business or conduct of the business of the
Seller or any of its Significant Subsidiaries.

     "REPRESENTATIVE(S)" shall have the meaning ascribed thereto in Section
5.02(b) hereof.

     "REQUISITE REGULATORY APPROVALS" shall have the meaning ascribed thereto in
Section 6.01(b) hereof.

     "SEC" shall have the meaning ascribed thereto in Section 3.04 hereof.

     "S-4" shall have the meaning ascribed thereto in Section 5.04(a) hereof.

     "SECURITIES ACT" shall mean the Securities Act of 1933, as amended.

     "SELLER" shall have the meaning ascribed thereto in the preamble to this
Agreement and, in addition, shall mean throughout this Agreement, unless the
context contemplates otherwise, the Seller and each of its subsidiaries,
considered separately and on a consolidated basis.

     "SELLER AFFILIATES" shall have the meaning ascribed thereto in Section
5.06(a) hereof.

     "SELLER AFFILIATES AGREEMENT" shall mean the form of written agreement to
be executed and delivered to the Buyer prior to the Effective Time by the Seller
Affiliates, substantially in the form attached hereto as EXHIBIT B-2.

     "SELLER BALANCE SHEET" shall have the meaning ascribed thereto in Section
4.05 hereof.

     "SELLER BENEFIT PLANS" shall have the meaning ascribed thereto in Section
4.11(a) hereof.

     "SELLER COMMON STOCK" shall have the meaning ascribed thereto in Section
4.02(a) hereof.

     "SELLER COMPANIES" shall have the meaning ascribed thereto in Section
4.10(a) hereof.

     "SELLER DISCLOSURE SCHEDULE" shall have the meaning ascribed thereto in
Section 4.01(a) hereof.

     "SELLER OPTION" shall mean the option granted to the Buyer pursuant to the
Seller Option Agreement.

     "SELLER OPTION AGREEMENT" shall mean that certain Stock Option Agreement of
even date herewith by and between the Seller and the Buyer in the form attached
hereto as EXHIBIT C.

     "SELLER OTHER PLANS" shall have the meaning ascribed thereto in Section
4.11(a) hereof.

     "SELLER PENSION PLANS" shall have the meaning ascribed thereto in Section
4.11(a) hereof.

                                      A-4
<PAGE>   105

     "SELLER REPORTS" shall have the meaning ascribed thereto in Section 4.15
hereof.

     "STOCKHOLDER AGREEMENT" shall mean that certain Stockholder Agreement dated
as of the date hereof between the Buyer and Mr. Bradbury substantially in the
form attached hereto as EXHIBIT D.

     "SIGNIFICANT SUBSIDIARY" shall mean, when used with reference to a party,
any "significant subsidiary" of such party as such term is defined in Regulation
S-X of the SEC, and with respect to the Seller, the term "Significant
Subsidiary" shall also include Walden Financial Corporation, Builders
Collaborative, Inc., Walden Securities Corporation, Inc., Braintree Savings
Corporation, Bra-Prop Corporation and Braintree Securities Corporation.

     "SUBSIDIARIES" shall mean, when used with reference to a party, any
corporation or other organization, whether incorporated or unincorporated, of
which such party or any other subsidiary of such party is a general partner
(excluding partnerships the general partnership interests of which held by such
party or any subsidiary of such party do not have a majority of the voting
interests in such partnership) or, with respect to such corporation or other
organization, at least a majority of the securities or other interests having by
their terms ordinary voting power to elect a majority of the board of directors
or others performing similar functions is directly or indirectly owned or
controlled by such party or by any one or more of its subsidiaries, or by such
party and one or more of its subsidiaries.

     "TAX" means any federal, state, local or foreign income, gross receipts,
franchise, estimated, alternative minimum, add-on minimum, sales, use, transfer,
registration, value added, excise, natural resources, severance, stamp,
occupation, premium, windfall profit, environmental, customs, duties, real
property, personal property, capital stock, intangibles, social security,
unemployment, disability, payroll, license, employee or other tax or levy, of
any kind whatsoever, including any interest, penalties or additions to tax in
respect of the foregoing.

     "TAX RETURN" means any return, declaration, report, claim for refund,
information return or other document (including any related or supporting
estimates, elections, schedules, statements or information) filed or required to
be filed in connection with the determination, assessment or collection of any
Tax or the administration of any laws, regulations or administrative
requirements relating to any Tax.

     "TERMINATION DATE" shall have the meaning ascribed thereto in Section
8.01(b) hereof.

     "TRANSACTION DOCUMENTS" shall mean this Agreement, the Confidentiality
Agreement, the Plan of Merger, the Seller Option Agreement, the Shareholders
Agreement, and each other agreement, document or instrument executed in
connection herewith or therewith.

     "TRANSFERRED EMPLOYEE" shall have the meaning ascribed thereto in Section
5.13(a) hereof.

     "TRUST ACCOUNT SHARES" shall have the meaning ascribed thereto in Section
3.12 hereof.

                                   ARTICLE II

                                   THE MERGER
                                   ----------

     Subject to the terms and conditions of this Agreement and the Plan of
Merger, the Merger Subsidiary will merge with and into the Seller (the
"MERGER"), with the Seller being the surviving corporation, pursuant to the
provisions of, and with the effect provided in, the MBCL. The Plan of 

                                      A-5
<PAGE>   106

Merger provides for the terms and conditions of the Merger, including but not
limited to the conversion and exchange of Seller Common Stock for Buyer Common
Stock, all of which are incorporated herein and made a part of this Agreement by
reference whether or not the Plan of Merger is executed on or subsequent to the
date hereof.

                                   ARTICLE III

                   REPRESENTATIONS AND WARRANTIES OF THE BUYER
                   -------------------------------------------

     The Buyer hereby represents and warrants to the Seller as follows:

     3.01 Corporate Organization.
          ----------------------

          (a) The Buyer is a corporation duly organized, validly existing and in
     good standing under the laws of The Commonwealth of Massachusetts. The
     Buyer has all requisite corporate power and authority to own, lease or
     operate all of its properties and assets and to carry on its business as it
     is now being conducted. The Buyer is duly licensed or qualified to do
     business in each jurisdiction in which the nature of the business conducted
     by it or the character or location of the properties and assets owned,
     leased or operated by it makes such licensing or qualification necessary,
     except where the failure to be so licensed or qualified would not result
     in, with respect to the Buyer, a Material Adverse Effect. The Buyer is a
     bank holding company registered with the Federal Reserve Board under the
     BHCA.

          (b) Except as set forth in Section 3.01 of the disclosure schedule
     which is being delivered to the Seller together herewith (the "BUYER
     DISCLOSURE SCHEDULE"), the Buyer has no subsidiaries and no Equity
     Investments (other than its investments in such subsidiaries).

          (c) Each Significant Subsidiary of the Buyer is duly organized,
     validly existing and in corporate good standing under the laws of the
     jurisdiction of its incorporation. Each Significant Subsidiary of the Buyer
     has all requisite corporate power and authority to own, lease or operate
     all of its properties and assets and to carry on its business as it is now
     being conducted. Each Significant Subsidiary is duly licensed or qualified
     to do business in each jurisdiction in which the nature of the business
     conducted by it or the character or location of the properties and assets
     owned, leased, or operated by it makes such licensing or qualification
     necessary, except where the failure to be so licensed or qualified would
     neither individually nor in the aggregate result in any Material Adverse
     Effect on the Buyer or such Significant Subsidiary.

     3.02 Capitalization.
          --------------

          (a) The authorized capital stock of the Buyer consists of 30,000,000
     shares of common stock, par value $0.625 per share ("BUYER COMMON STOCK"),
     and 4,000,000 shares of preferred stock, par value $1.00 per share ("BUYER
     PREFERRED STOCK"). As of the close of business on July 31, 1996, there were
     17,901,990 shares of Buyer Common Stock and no shares of Buyer Preferred
     Stock issued and outstanding. In addition, as of the close of business on
     July 31, 1996, there were 1,367,440 shares of Buyer Common Stock reserved
     for issuance upon exercise of outstanding stock options. All issued and
     outstanding shares of Buyer Common Stock and Buyer Preferred Stock have
     been duly authorized and validly issued and are fully paid, nonassessable
     and free of preemptive rights, with no personal liability attaching to the
     ownership thereof. Except for rights issuable in accordance with the Buyer
     Rights Agreement upon the issuance of Buyer Common Stock as permitted under
     this Agreement or as referred to in this Section 3.02 or reflected in
     Section 3.02(a) of the Buyer Disclosure Schedule, the Buyer does not have
     and is not bound by any 

                                      A-6
<PAGE>   107

     outstanding subscriptions, options, warrants, calls, commitments, rights
     agreements or agreements of any character calling for the Buyer to issue,
     deliver or sell, or cause to be issued, delivered or sold any shares of
     Buyer Common Stock or Buyer Preferred Stock or any other equity security of
     the Buyer or any subsidiary of the Buyer or any securities convertible
     into, exchangeable for or representing the right to subscribe for, purchase
     or otherwise receive any shares of Buyer Common Stock or Buyer Preferred
     Stock or any other equity security of the Buyer or any subsidiary of the
     Buyer or obligating the Buyer to grant, extend or enter into any such
     subscriptions, options, warrants, calls, commitments, rights agreements or
     agreements. As of the date hereof there are no outstanding contractual
     obligations of the Buyer to repurchase, redeem or otherwise acquire any
     shares of capital stock of the Buyer or any subsidiary of the Buyer.

          (b) Section 3.02(b) of the Buyer Disclosure Schedule lists each of the
     Significant Subsidiaries of the Buyer on the date of this Agreement and
     indicates for each such subsidiary as of such date: (i) the percentage and
     type of equity securities owned or controlled by the Buyer; (ii) the
     jurisdiction of incorporation; and (iii) if the subsidiary is a depository
     institution, whether it is a member of the Federal Reserve System. Each of
     the subsidiaries of the Buyer that is a depository institution is an
     "insured depository institution" as defined in the FDIA and applicable
     regulations thereunder, and the deposits of each such depository
     institution are insured by the Bank Insurance Fund of the FDIC in
     accordance with the FDIA, and each such depository institution has paid all
     assessments and filed all reports required by the FDIA. As of the date
     hereof, no proceedings for the revocation or termination of such deposit
     insurance are pending or, to the knowledge of the Buyer, threatened. No
     subsidiary of the Buyer has or is bound by any outstanding subscriptions,
     options, warrants, calls, commitments or agreements of any character
     calling for a subsidiary of the Buyer to issue deliver or sell, or cause to
     be issued, delivered or sold any equity security of the Buyer or of any
     subsidiary of the Buyer or any securities convertible into, exchangeable
     for or representing the right to subscribe for, purchase or otherwise
     receive any such equity security or obligating a subsidiary of the Buyer to
     grant, extend or enter into any such subscriptions, options, warrants,
     calls, commitments or agreements. As of the date hereof, there are no
     outstanding contractual obligations of any subsidiary of the Buyer to
     repurchase, redeem or otherwise acquire any shares of capital stock of the
     Buyer or any subsidiary of the Buyer. Except as may be provided under
     applicable law in the case of any subsidiary of the Buyer that is a bank,
     all of the shares of capital stock of each of the subsidiaries of the Buyer
     held by the Buyer are fully paid and nonassessable and, except for
     directors' qualifying shares, are owned by the Buyer free and clear of any
     claim, lien, encumbrance or agreement with respect thereto.

     3.03 Authority; No Violation.
          -----------------------

          (a) The Buyer has all requisite corporate power and authority to
     execute and deliver the Transaction Documents to which it is a party and to
     consummate the transactions contemplated thereby. The Merger Subsidiary has
     or will have prior to the Closing Date all requisite corporate power and
     authority to execute and deliver the Plan of Merger and to consummate the
     transactions contemplated thereby. The execution and delivery of this
     Agreement and the other Transaction Documents to which the Buyer is a party
     and the consummation of the transactions contemplated hereby and thereby
     have been duly and validly approved by the Board of Directors of the Buyer.
     The execution and delivery of the Plan of Merger and the consummation of
     the transactions contemplated thereby have been or will be prior to the
     Closing Date duly and validly approved by the Buyer, as sole stockholder of
     the Merger Subsidiary, and by the Board of Directors of the Merger
     Subsidiary. The Board of Directors of the Buyer has directed that this
     Agreement and the Plan of Merger and the transactions contemplated hereby
     and thereby be submitted to the stockholders of the Buyer for approval at a
     meeting of such stockholders, and except for the adoption of this 

                                      A-7

<PAGE>   108

     Agreement and the Plan of Merger by the Buyer's stockholders, no other
     corporate proceedings on the part of the Buyer are necessary to consummate
     any of the transactions so contemplated by the Transaction Documents. This
     Agreement and the Seller Option Agreement have been, and the Plan of Merger
     and the other Transaction Documents to be executed by the Buyer will be,
     duly and validly executed and delivered by the Buyer and (assuming due
     authorization, execution and delivery by the Seller) constitute (or, in the
     case of the Plan of Merger or such other Transaction Documents, will
     constitute at Closing) the valid and binding obligations of the Buyer,
     enforceable against the Buyer in accordance with their respective terms,
     except that enforcement thereof may be limited by the receivership,
     conservatorship and supervisory powers of bank regulatory agencies
     generally as well as bankruptcy, insolvency, reorganization, moratorium or
     other similar laws affecting enforcement of creditors' rights generally and
     except that enforcement thereof may be subject to general principles of
     equity (regardless of whether enforcement is considered in a proceeding in
     equity or at law) and the availability of equitable remedies.

          (b) Neither the execution and delivery of any of the Transaction
     Documents by the Buyer nor the consummation by the Buyer of the
     transactions contemplated thereby, nor compliance by the Buyer with any of
     the terms or provisions thereof, will (i) assuming that the consents and
     approvals referred to in Section 3.04 hereof are duly obtained, violate any
     statute, code, ordinance, rule, regulation, judgment, order, writ, decree
     or injunction applicable to the Buyer or any of its subsidiaries or any of
     their respective properties or assets, or (ii) violate, conflict with,
     result in a breach of any provisions of, constitute a default (or an event
     which, with notice or lapse of time, or both, would constitute a default)
     under, result in the termination of, accelerate the performance required
     by, or result in a right of termination or acceleration or the creation of
     any lien, security interest, charge or other encumbrance upon any of the
     respective properties or assets of the Buyer or any of its subsidiaries
     under, any of the terms, conditions or provisions of (A) the Articles of
     Organization or other charter document of like nature or By-Laws of the
     Buyer, or such subsidiary, as the case may be, or (B) any note, bond,
     mortgage, indenture, deed of trust, license, lease, agreement or other
     instrument or obligation to which the Buyer or any of its subsidiaries is a
     party as issuer, guarantor or obligor, or by which they or any of their
     respective properties or assets may be bound or affected, except, in the
     case of clause (ii)(B) above, for such violations, conflicts, breaches or
     defaults which either individually or in the aggregate will not result,
     with respect to the Buyer or any Significant Subsidiary of the Buyer, in a
     Material Adverse Effect.

     3.04 CONSENTS AND APPROVALS. Except for consents, waivers or approvals of,
or filings or registrations with, the Federal Reserve Board, the Board of Bank
Incorporation of The Commonwealth of Massachusetts (the "MASSACHUSETTS BOARD"),
the Securities and Exchange Commission (the "SEC"), the Secretary of State of
The Commonwealth of Massachusetts, NASDAQ, certain state "Blue Sky" or
securities commissioners, the DOJ and the stockholders of the Seller, no
consents, waivers or approvals of or filings or registrations with any public
body or authority are necessary, and no consents or approvals of any third
parties (which term does not include the Board of Directors of the Buyer or the
Merger Subsidiary) are necessary, in connection with (a) the execution and
delivery by the Buyer of the Transaction Documents to which it is a party, (b)
the execution and delivery by the Merger Subsidiary of the Plan of Merger, or
(c) the consummation by the Buyer or the Merger Subsidiary, as the case may be,
of the transactions contemplated by the Transaction Documents. The affirmative
vote of holders of a majority of the outstanding shares of Buyer Common Stock
who are present and voting at a meeting called for such purpose is the only vote
of the holders of any class or series of capital stock or other securities of
the Buyer necessary to approve of the Transaction Documents and the transactions
contemplated thereby. Other than as publicly disclosed, the Buyer has no
knowledge of any fact or circumstance relating to the Buyer or its subsidiaries
that is reasonably likely to materially impede or delay receipt of any Consents
of 

                                      A-8
<PAGE>   109

regulatory or governmental authorities or result in the imposition of a
restriction or condition of the type referenced in Section 6.02(g) herein.

     3.05 FINANCIAL STATEMENTS. The Buyer has made available to the Seller
copies of (a) the consolidated balance sheets of the Buyer and its subsidiaries
as of December 31 for the fiscal years 1993 through 1995, inclusive, and the
related consolidated statements of income, changes in stockholders' equity and
cash flows for the fiscal years 1993 through 1995, inclusive, as reported in the
Annual Reports of the Buyer on Form 10-K for each of the three (3) fiscal years
ended December 31, 1993 through December 31, 1995 which were filed with the SEC
under the Securities Exchange Act of 1934, as amended (the "EXCHANGE ACT"), in
each case accompanied by the audit report of Arthur Andersen LLP, independent
accountants for the Buyer, and (b) the unaudited consolidated balance sheets of
the Buyer and its subsidiaries as of June 30, 1996 and June 30, 1995, the
related unaudited consolidated statements of income and changes in stockholders'
equity for the six (6) months ended June 30, 1996 and June 30, 1995 and the
related unaudited consolidated statements of cash flows for the six (6) months
ended June 30, 1996 and June 30, 1995, all as reported in the Buyer's Quarterly
Report on Form 10-Q for the quarter ended June 30, 1996 filed with the SEC under
the Exchange Act. The December 31, 1995 consolidated balance sheet (the "BUYER
BALANCE SHEET") of the Buyer (including the related notes, where applicable) and
the other financial statements referred to herein (including the related notes,
where applicable) fairly present, and the financial statements to be included in
any reports or statements (including reports on Forms 10-Q and 10-K) to be filed
by the Buyer with the SEC after the date hereof will fairly present, the
consolidated financial position and results of the consolidated operations and
cash flows and changes in stockholders' equity of the Buyer and its subsidiaries
for the respective fiscal periods or as of the respective dates therein set
forth; and each of such statements (including the related notes, where
applicable) has been and will be prepared in accordance with GAAP consistently
applied during the periods involved, except as otherwise set forth in the notes
thereto (subject, in the case of unaudited interim statements, to normal
year-end adjustments). The books and records of the Buyer and its subsidiaries
have been, and are being, maintained in accordance with GAAP and applicable
legal and regulatory requirements.

     3.06 ABSENCE OF UNDISCLOSED LIABILITIES. None of the Buyer or any of its
subsidiaries has any obligation or liability (contingent or otherwise) that is
material on a consolidated basis to the Buyer, or that when combined with all
similar obligations or liabilities would be material on a consolidated basis to
the Buyer or any of its Significant Subsidiaries, except as disclosed or
reflected in the Buyer Balance Sheet or any of the other financial statements of
the Buyer described in Section 3.05 above.

     3.07 BROKER'S FEES. Neither the Buyer nor any of its officers, directors,
employees or agents has employed any broker, finder or financial advisor or
incurred any liability for any fees or commissions in connection with any of the
transactions contemplated by this Agreement, except for the fees incurred in
connection with the engagement of Fox-Pitt, Kelton Inc. and for legal,
accounting and other professional fees payable in connection with the Merger.
The Buyer will be responsible for the payment of all such fees.

     3.08 ABSENCE OF CERTAIN CHANGES OR EVENTS. Except as disclosed in the
Buyer's Quarterly Report on Form 10-Q for the quarter ended June 30, 1996 or in
any Current Reports of the Buyer on Form 8-K filed prior to the date of this
Agreement, since December 31, 1995, the Buyer and its subsidiaries have not
incurred any material liability, except in the ordinary course of their business
consistent with their past practices, nor has there been any change in the
business, assets, financial condition or results of operations of the Buyer or
any of its subsidiaries which has had, or is reasonably likely to have,
individually or in the aggregate, a Material Adverse Effect on the Buyer or any
Significant Subsidiary of the Buyer.

                                      A-9
<PAGE>   110


     3.09 LEGAL PROCEEDINGS. There is no suit, action or proceeding pending or,
to the best knowledge of the Buyer, threatened, against the Buyer or any
subsidiary of the Buyer or challenging the validity or propriety of the
transactions contemplated by this Agreement or the Plan of Merger, as to which
there is a reasonable possibility of an adverse determination and which, if
adversely determined, would, individually or in the aggregate, have a Material
Adverse Effect on the Buyer or any Significant Subsidiary of the Buyer or
otherwise materially adversely affect the Buyer's ability to perform its
obligations under this Agreement, nor is there any judgment, decree, injunction,
rule or order of any legal or administrative body or arbitrator outstanding
against the Buyer or any subsidiary of the Buyer having, or which insofar as
reasonably can be foreseen, in the future could have, any such effect.

     3.10 REPORTS. Since January 1, 1993, the Buyer and its subsidiaries have
filed, and subsequent to the date hereof will file, all reports, registrations
and statements, together with any amendments required to be made with respect
thereto, that were and are required to be filed with (a) the SEC, including, but
not limited to, Forms 10-K, Forms 10-Q, Forms 8-K and proxy statements (and all
such reports, registrations and statements have been or will be delivered by the
Buyer to the Seller), (b) the Federal Reserve Board, (c) the FDIC, and (d) any
applicable state securities or banking authorities (except, in the case of state
securities authorities, no such representation is made as to filings which are
not material) (all such reports and statements are collectively referred to
herein as the "BUYER REPORTS"). As of their respective dates, the Buyer Reports
complied and, with respect to filings made after the date of this Agreement,
will at the date of filing comply, in all material respects with all of the
statutes, rules and regulations enforced or promulgated by the regulatory
authority with which they were filed and did not contain and, with respect to
filings made after the date of this Agreement, will not at the date of filing
contain, any untrue statement of a material fact or omit to state a material
fact required to be stated therein or necessary in order to make the statements
therein, in light of the circumstances under which they were made, not
misleading.

     3.11 BUYER COMMON STOCK. Buyer Common Stock to be issued pursuant to the
Plan of Merger is duly authorized and, when issued at the Effective Time, will
be validly issued, fully paid and nonassessable and not subject to preemptive
rights, with no personal liability attaching thereto.

     3.12 OWNERSHIP OF SELLER COMMON STOCK. Neither the Buyer nor, to its best
knowledge, any of its affiliates or associates (as such terms are defined under
the Exchange Act) (a) beneficially own, directly or indirectly, or (b) are
parties to any agreement, arrangement or understanding for the purpose of
acquiring, holding, voting or disposing of, in each case, shares of capital
stock of the Seller, which in the aggregate represent five percent (5%) or more
of the outstanding shares of capital stock of the Seller entitled to vote
generally in the election of directors (other than shares in trust accounts,
managed accounts and the like that are beneficially owned by third parties (any
such shares, "TRUST ACCOUNT SHARES")).

     3.13 Taxes and Tax Returns.
          ---------------------

          (a) Except where the failure to do so would not have a Material
     Adverse Effect, the Buyer and each of its subsidiaries (referred to for
     purposes of this Section 3.13, collectively, as the "BUYER COMPANIES")
     have, since December 31 1989, timely filed in correct form all Filed Tax
     Returns.

          (b) The Buyer Companies have paid all Taxes shown as being due on the
     Filed Tax Returns.

          (c) No assessment that has not been settled or otherwise resolved has
     been made with respect to Taxes not shown on the Filed Tax Returns, other
     than such additional Taxes as are being contested in good faith and which
     if determined adversely to the Buyer 



                                      A-10

<PAGE>   111

     Companies would not have a Material Adverse Effect. No deficiency in Taxes
     or other proposed adjustment that has not been settled or otherwise
     resolved has been asserted in writing by any taxing authority against any
     of the Buyer Companies, which if determined adversely to the Buyer
     Companies would have a Material Adverse Effect. No material Tax Return of
     any of the Buyer Companies is now under examination by any applicable
     taxing authority. There are no material liens for Taxes (other than current
     Taxes not yet due and payable) on any of the assets of any Buyer Company.

          (d) Adequate provision has been made on the Buyer Balance Sheet for
     all Taxes of the Buyer Companies in respect of all periods through the date
     hereof.

          (e) Except with respect to intra-Buyer Company agreements made or
     required under the federal consolidated tax return regulations, none of the
     Buyer Companies is a party to or bound by any Tax indemnification, Tax
     allocation or Tax sharing agreement with any person or entity or has any
     current or potential contractual obligation to indemnify any other person
     or entity with respect to Taxes.

          (f) None of the Buyer Companies has filed or been included in a
     combined, consolidated or unitary income Tax Return (including any
     consolidated federal income Tax Return) other than one of which one of the
     Buyer Companies was the parent.

          (g) None of the Buyer Companies has made any payments, is obligated to
     make any payments, or is a party to any agreement that could obligate it to
     make any payments that will not be deductible under Code Section 280G.

     3.14 Employees.
          ---------

          (a) The current value of the assets of each of the "employee pension
     benefit plans", as such term is defined in Section 3 of ERISA, which is
     maintained or contributed to by the Buyer (each a "BUYER PENSION PLAN"),
     and which is subject to Title IV of ERISA, exceeds that plan's "Benefit
     Liabilities" as that term is defined in Section 4001(a)(16) of ERISA, when
     determined under actuarial factors that would apply if that plan terminated
     in accordance with all applicable legal requirements.

          (b) To the best knowledge of the Buyer, each of the Buyer Pension
     Plans and each of the "employee welfare benefit plans" (the "BUYER BENEFIT
     PLANS"), as such term is defined in Section 3 of ERISA, which is maintained
     or contributed to by the Buyer, has been administered in compliance with
     its terms in all material respects and is in compliance in all material
     respects with the applicable provisions of ERISA (including, but not
     limited to, the funding and prohibited transactions provisions thereof),
     the Code and other applicable laws, except to the extent that
     non-compliance would not have a Material Adverse Effect on the Buyer, taken
     as a whole.

          (c) To the best knowledge of the Buyer, there has been no reportable
     event within the meaning of Section 4043(b) of ERISA or any waived funding
     deficiency within the meaning of Section 412(d)(3) (or any predecessor
     section) of the Code with respect to any Buyer Pension Plan.

          (d) To the best knowledge of the Buyer, each of the Buyer Pension
     Plans which is intended to be a qualified plan within the meaning of
     Section 401(a) of the Code is so qualified, and the Buyer is not aware of
     any fact or circumstance which would adversely affect the qualified status
     of any such plan.


                                      A-11
<PAGE>   112

     3.15 AGREEMENTS WITH BANKING AUTHORITIES. Neither the Buyer nor any of its
subsidiaries is a party to any commitment, letter (other than letters addressed
to regulated depository institutions generally), written agreement, memorandum
of understanding or order to cease and desist with any federal or state
governmental entity charged with the supervision or regulation of banks or bank
holding companies or engaged in the insurance of bank deposits which restricts
materially the conduct of its business, or in any manner relates to its capital
adequacy, credit policies, management or overall safety and soundness or such
entity's ability to perform its obligations hereunder, and neither the Buyer nor
any of its subsidiaries has received written notification from any such federal
or state governmental entity that any such Person may be requested to enter
into, or otherwise be subject to, any such commitment, letter, written
agreement, memorandum of understanding or cease and desist order.

     3.16 COMPLIANCE WITH APPLICABLE LAW. Each of the Buyer and each Significant
Subsidiary thereof holds all licenses, franchises, permits and authorizations
necessary for the lawful conduct of its business, and each of the Buyer and each
Significant Subsidiary thereof has complied with and is not in violation of or
default in any respect under any, applicable law, statute, order, rule,
regulation or policy of, or agreement with, any federal, state or local
governmental agency or authority relating to the Buyer or such Significant
Subsidiary (other than where such default or noncompliance will not result in,
or create the possibility of resulting in, a material limitation on the conduct
of the business of the Buyer, will not cause, or create the possibility of
causing, the Buyer or any Significant Subsidiary thereof to incur any financial
penalty in excess of $20,000 (including but not limited to any civil money
penalty or other monetary sanction under Section 8(i)(2) of the FDIA, 12 U.S.C.
[Section]1818(i)(2), or under any applicable state law ("CMPs")), and will not
otherwise result, or create the possibility of resulting in any Material Adverse
Effect on the Buyer or any Significant Subsidiary of the Buyer), and neither the
Buyer nor any Significant Subsidiary of the Buyer has received any notice of any
violation of any such law, statute, order, rule, regulation, policy or
agreement, or the commencement of any proceeding in connection with any such
violation (including but not limited to any hearing or investigation relating to
the imposition or contemplated imposition of CMPs), and does not know of any
violation of, any such law, statute, order, rule, regulation, policy or
agreement which would have such a result.

     3.17 CAPITALIZATION. As of the date hereof, without giving effect to the
transactions contemplated hereby, the subsidiaries of the Buyer which are
"insured depository institutions" (a) are "well capitalized", as defined in the
FDIA, and (b) meet all capital requirements, standards and ratios required by
each state or federal bank regulator with jurisdiction over such Persons. No
such regulator has indicated that it will condition any of the regulatory
approvals upon an increase in any such Person's capital or compliance with any
special capital requirement, standard or ratio.

     3.18 CRA RATING. Each subsidiary of the Buyer which is an "insured
depository institution" was rated "Satisfactory" or better following its most
recent Community Reinvestment Act examination by the regulatory agency
responsible for its supervision. Neither the Buyer nor any of such subsidiaries
has received any notice of and none of such Persons has any knowledge of any
planned or threatened objection by any community group to the transactions
contemplated hereby.

     3.19 BUYER INFORMATION. The information relating to the Buyer and its
subsidiaries to be contained in the Joint Proxy Statement and the S-4, as
described in Section 5.04 hereof, and any other documents filed with the SEC or
any regulatory agency in connection herewith, to the extent such information is
provided in writing by the Buyer, will not contain any untrue statement of a
material fact or omit to state a material fact necessary to make such
information not misleading.

     3.20 DISCLOSURE. No representation or warranty contained in this Agreement,
and no statement contained in any certificate, list or other writing, including
but not necessarily limited to the Buyer Disclosure Schedule, furnished to the
Seller pursuant to the provisions hereof, to the best knowledge of the Buyer,
contains or will contain any untrue statement of a material fact or omits to

                                      A-12
<PAGE>   113

state a material fact necessary in order to make the statements herein or
therein not misleading. To the best knowledge of the Buyer, all information
material to the Merger and the transactions contemplated by this Agreement, or
which is necessary to make the representations and warranties herein contained
not misleading, has been disclosed in writing to the Seller.

                                   ARTICLE IV

                  REPRESENTATIONS AND WARRANTIES OF THE SELLER
                  --------------------------------------------

     The Seller hereby represents and warrants to the Buyer as follows:

     4.01 Corporate Organization.
          ----------------------

          (a) The Seller is a corporation duly organized, validly existing and
     in good standing under the laws of The Commonwealth of Massachusetts. The
     Seller has all requisite corporate power and authority to own, lease or
     operate all of its properties and assets and to carry on its business as it
     is now being conducted. The Seller is duly licensed or qualified to do
     business in each jurisdiction in which the nature of the business conducted
     by it or the character or location of the properties and assets owned,
     leased or operated by it makes such licensing or qualification necessary,
     except where the failure to be so licensed or qualified would not result
     in, with respect to the Seller, any Material Adverse Effect. The Seller is
     a bank holding company registered with the Federal Reserve Board under the
     BHCA.

          (b) Except as set forth in Section 4.01 of the disclosure schedule
     delivered to the Buyer together herewith (the "SELLER DISCLOSURE
     SCHEDULE"), the Seller has no subsidiaries and no Equity Investments (other
     than its investments in such subsidiaries).

          (c) Each Significant Subsidiary of the Seller is duly organized,
     validly existing and in corporate good standing under the laws of the
     jurisdiction of its incorporation. Each Significant Subsidiary of the
     Seller has all requisite corporate power and authority to own, lease or
     operate all of its properties and assets and to carry on its business as it
     is now being conducted. Each Significant Subsidiary is duly licensed or
     qualified to do business in each jurisdiction in which the nature of the
     business conducted by it or the character or location of the properties and
     assets owned, leased or operated by it makes such licensing or
     qualification necessary, except where the failure to be so licensed or
     qualified would, neither individually nor in the aggregate, result in any
     Material Adverse Effect on the Seller or such Significant Subsidiary.

          (d) The minute books of the Seller contain complete and accurate
     records of all meetings and other corporate actions authorized at such
     meetings held or taken since January 1, 1993 to date of its stockholders
     and Board of Directors.

     4.02 Capitalization.
          --------------

          (a) The authorized capital stock of the Seller consists of 10,000,000
     shares of common stock, par value $1.00 per share ("SELLER COMMON STOCK").
     As of the close of business on August 28, 1996, there were 5,109,892 shares
     of Seller Common Stock issued and outstanding. In addition, as of the close
     of business on August 28, 1996, there were 468,934 shares of Seller Common
     Stock reserved for issuance upon the exercise of outstanding stock options
     and incentive plans and 219,006 shares of Seller Common Stock reserved for
     issuance under the 1993 Employee Stock Purchase Plan. All issued and
     outstanding shares of Seller Common Stock have been duly authorized and
     validly issued and are fully paid, nonassessable and free of preemptive
     rights, with no personal liability attaching to the 

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     ownership thereof. Except as referred to in this Section 4.02, the Seller
     does not have and is not bound by any outstanding subscriptions, options,
     warrants, calls, commitments, rights agreements or agreements of any
     character calling for the Seller to issue, deliver or sell, or cause to be
     issued, delivered or sold any shares of Seller Common Stock or any other
     equity security of the Seller or any subsidiary of the Seller or any
     securities convertible into, exchangeable for or representing the right to
     subscribe for, purchase or otherwise receive any shares of Seller Common
     Stock or any other equity security of the Seller or any subsidiary of the
     Seller or obligating the Seller to grant, extend or enter into any such
     subscriptions, options, warrants, calls, commitments, rights agreements or
     agreements. As of the date hereof, there are no outstanding contractual
     obligations of the Seller to repurchase, redeem or otherwise acquire any
     shares of capital stock of the Seller or any subsidiary of the Seller. In
     addition, Section 4.02(a) of the Seller Disclosure Schedule sets forth, as
     of the date hereof, the number of shares of Seller Common Stock subject to
     outstanding stock options, the various dates on which such options were
     granted, the various exercise prices for such options, the number of shares
     for which such options are presently vested and the vesting schedule for
     the remaining balance of shares for which such options are not presently
     vested.

          (b) Section 4.02(b) of the Seller Disclosure Schedule lists each of
     the Significant Subsidiaries of the Seller as of the date of this Agreement
     and indicates for each such subsidiary as of such date: (i) the percentage
     and type of equity securities owned or controlled by the Seller; (ii) the
     jurisdiction of incorporation; and (iii) if the subsidiary is a depository
     institution, whether it is a member of the Federal Reserve System. Each of
     the subsidiaries of the Seller that is a depository institution is an
     "insured depository institution" as defined in the FDIA and applicable
     regulations thereunder, and the deposits of each such depository
     institution are insured by the Bank Insurance Fund of the FDIC in
     accordance with the FDIA. Further, The Share Insurance Fund of the
     Co-operative Central Bank insures deposits of The Co-operative Bank of
     Concord, and the Deposit Insurance Fund of the Mutual Savings Central Fund,
     Inc. of Massachusetts insures the deposits of The Braintree Savings Bank in
     each case in excess of the FDIC's insurance limits. Each such depository
     institution has paid all assessments and filed all reports required by the
     FDIA, the Deposit Insurance Fund and the Share Insurance Fund. As of the
     date hereof no proceedings for the revocation or termination of such
     deposit insurance are pending or to the knowledge of the Seller,
     threatened. No subsidiary of the Seller has or is bound by any outstanding
     subscriptions, options, warrants, calls, commitments or agreements of any
     character calling for a subsidiary of the Seller to issue, deliver or sell,
     or cause to be issued, delivered or sold, any equity security of the Seller
     or of any subsidiary of the Seller or any securities convertible into,
     exchangeable for or representing the right to subscribe for, purchase or
     otherwise receive any such equity security or obligating a subsidiary of
     the Seller to grant, extend or enter into any such subscriptions, options,
     warrants, calls, commitments or agreements. As of the date hereof, there
     are no outstanding contractual obligations of any subsidiary of the Seller
     to repurchase, redeem or otherwise acquire any shares of capital stock of
     the Seller or any subsidiary of the Seller. Except as may be provided under
     applicable law in the case of any subsidiary of the Seller that is a bank,
     all of the shares of capital stock of each of the subsidiaries held by the
     Seller are fully paid and nonassessable and, except for directors'
     qualifying shares, are owned by the Seller free and clear of any claim,
     lien, encumbrance or agreement with respect thereto.

     4.03 Authority; No Violation.
          -----------------------

          (a) The Seller has full corporate power and authority to execute and
     deliver the Transaction Documents to which it is a party and to consummate
     the transactions contemplated thereby. The execution and delivery of this
     Agreement and the other Transaction Documents to which the Seller is a
     party and the consummation of the 

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<PAGE>   115

     transactions contemplated hereby and thereby have been duly and validly
     approved by the Board of Directors of the Seller. The Board of Directors of
     the Seller has directed that this Agreement and the Plan of Merger and the
     transactions contemplated hereby and thereby be submitted to the
     stockholders of the Seller for approval at a meeting of such stockholders
     and, except for the adoption of this Agreement and the Plan of Merger by
     its stockholders, no other corporate proceedings on the part of the Seller
     are necessary to consummate any of the transactions so contemplated by the
     Transaction Documents. This Agreement and the Seller Option Agreement have
     been, and the Plan of Merger and the other Transaction Documents to be
     executed by the Seller will be, prior to the Closing Date, duly and validly
     executed and delivered by the Seller and (assuming due authorization,
     execution and delivery by the Buyer and, with respect to the Plan of
     Merger, the Merger Subsidiary) constitute (or, in the case of the Plan of
     Merger or such other Transaction Documents, will constitute at Closing) the
     valid and binding obligations of the Seller, enforceable against the Seller
     in accordance with their respective terms, except that enforcement thereof
     may be limited by the receivership, conservatorship and supervisory powers
     of bank regulatory agencies generally as well as bankruptcy, insolvency,
     reorganization, moratorium or other similar laws affecting enforcement of
     creditors' rights generally and except that enforcement thereof may be
     subject to general principles of equity (regardless of whether enforcement
     is considered in a proceeding in equity or at law) and the availability of
     equitable remedies.

          (b) Neither the execution and delivery of any of the Transaction
     Documents by the Seller, nor the consummation by the Seller of the
     transactions contemplated thereby, nor compliance by the Seller with any of
     the terms or provisions thereof, will (i) assuming that the consents and
     approvals referred to in Section 4.04 are duly obtained, violate any
     statute, code, ordinance, rule, regulation, judgment, order, writ, decree
     or injunction applicable to the Seller or any of its subsidiaries or any of
     their respective properties or assets, or (ii) violate, conflict with,
     result in a breach of any provisions of, constitute a default (or an event
     which, with notice or lapse of time, or both, would constitute a default)
     under, result in the termination of, accelerate the performance required
     by, or result in a right of termination or acceleration or the creation of
     any lien, security interest, charge or other encumbrance upon any of the
     respective properties or assets of the Seller or any of its subsidiaries
     under, any of the terms, conditions or provisions of (A) the Articles of
     Organization or other charter document of like nature or By-Laws of the
     Seller or such subsidiary, as the case may be, or (B) any note, bond,
     mortgage, indenture, deed of trust, license, lease, agreement or other
     instrument or obligation to which the Seller or any of its subsidiaries is
     a party as issuer, guarantor or obligor, or by which they or any of their
     respective properties or assets may be bound or affected, except, in the
     case of clause (ii)(B) above, for such violations, conflicts, breaches or
     defaults which either individually or in the aggregate will not result,
     with respect to the Seller or any Significant Subsidiary of the Seller, in
     any Material Adverse Effect.

     4.04 CONSENTS AND APPROVALS. Except for consents, waivers or approvals of,
or filings or registrations with, the Federal Reserve Board, the Massachusetts
Board, the SEC, the Secretary of State of The Commonwealth of Massachusetts,
NASDAQ, certain state "Blue Sky" or securities commissioners, the DOJ and the
stockholders of the Seller, no consents, waivers or approvals of or filings or
registrations with any public body or authority are necessary, and no consents
or approvals of any third parties (which term does not include the Board of
Directors of the Seller or any subsidiary of the Seller) are necessary, in
connection with (a) the execution and delivery by the Seller of the Transaction
Documents to which it is a party or (b) the consummation by the Seller of the
transactions contemplated by such agreements. The affirmative vote of holders of
two-thirds of the outstanding shares of Seller Common Stock is the only vote of
the holders of any class or series of capital stock or other securities of the
Seller necessary to approve of the Transaction Documents and the transactions
contemplated thereby.

    
                                      A-15
<PAGE>   116

     4.05 FINANCIAL STATEMENTS. The Seller has made available to the Buyer
copies of (a) the consolidated balance sheets of the Seller and its subsidiaries
as of December 31, 1995 and the consolidated balance sheets of each of The
Braintree Savings Bank and The Co-operative Bank of Concord for the fiscal years
1993 through 1995, inclusive, and the related consolidated statements of
operations, changes in stockholders' equity and cash flows for the fiscal years
1993 through 1995, inclusive, as reported in the Seller's Annual Reports on Form
10-K or such Significant Subsidiaries' Annual Reports on Form F-2 for each of
the three (3) fiscal years ended December 31, 1993 through December 31, 1995
which were filed with the SEC or the FDIC (as applicable) under the Exchange
Act, in each case accompanied by the audit report of Arthur Andersen LLP or such
other independent accountants for such Significant Subsidiaries, and (b) the
unaudited consolidated balance sheets of the Seller and its subsidiaries as of
June 30, 1996 and June 30, 1995, the related unaudited consolidated statements
of operations and changes in stockholders' equity for the six (6) months ended
June 30, 1996 and June 30, 1995 and the related unaudited consolidated
statements of cash flows for the six (6) months ended June 30, 1996 and June 30,
1995, all as reported in the Seller's Quarterly Report on Form 10-Q for the six
(6) months ended June 30, 1996 filed with the SEC under the Exchange Act. The
December 31, 1995 consolidated balance sheet (the "SELLER BALANCE SHEET") of the
Seller (including the related notes, where applicable) and the other financial
statements referred to herein (including the related notes, where applicable)
fairly present, and the financial statements to be included in any reports or
statements (including reports on Forms 10-Q and 10-K) to be filed by the Seller
with the SEC after the date hereof will fairly present, the consolidated
financial position and results of the consolidated operations and cash flows and
changes in shareholders' equity of the Seller and its subsidiaries for the
respective fiscal periods or as of the respective dates therein set forth; and
each of such statements (including the related notes, where applicable) has been
and will be prepared in accordance with GAAP consistently applied during the
periods involved, except as otherwise set forth in the notes thereto (subject,
in the case of unaudited interim statements, to normal year-end adjustments).
The books and records of the Seller and its subsidiaries have been, and are
being, maintained in accordance with GAAP and applicable legal and regulatory
requirements.

     4.06 ABSENCE OF UNDISCLOSED LIABILITIES. None of the Seller or any of its
subsidiaries has any obligation or liability (contingent or otherwise) that is
material on a consolidated basis to the Seller, or that when combined with all
similar obligations or liabilities would be material on a consolidated basis to
the Seller or any of its Significant Subsidiaries, except as disclosed or
reflected in the Seller Balance Sheet or any of the other financial statements
described in Section 4.05 above.

     4.07 BROKER'S FEES. Neither the Seller nor any of its officers, directors,
employees or agents has employed any broker, finder or financial advisor or
incurred any liability for any fees or commissions in connection with any of the
transactions contemplated by this Agreement, except for the fees incurred in
connection with the engagement of PaineWebber and except for legal, accounting
and other professional fees payable in connection with the Merger. The Seller
will be responsible for the payment of all such fees.

     4.08 ABSENCE OF CERTAIN CHANGES OR EVENTS. Except as disclosed in the
Seller's Quarterly Report on Form 10-Q for the six (6) months ended June 30,
1996 or in any Current Reports of the Seller on Form 8-K filed prior to the date
of this Agreement, since December 31, 1995, the Seller and its subsidiaries have
not incurred any material liability, except in the ordinary course of their
business consistent with their past practices, nor has there been any change in
the business, assets, financial condition or results of operations of the Seller
or any of its subsidiaries which has had, or is reasonably likely to have,
individually or in the aggregate, a Material Adverse Effect on the Seller or any
Significant Subsidiary of the Seller.

     4.09 LEGAL PROCEEDINGS. There is no suit, action or proceeding pending or,
to the best knowledge of the Seller, threatened, against the Seller or any
subsidiary of the Seller or challenging the validity or propriety of the
transactions contemplated by this Agreement or the Plan of Merger, 

                                      A-16

<PAGE>   117

as to which there is a reasonable possibility of an adverse determination and
which, if adversely determined, would, individually or in the aggregate, have a
Material Adverse Effect on the Seller or any Significant Subsidiary of the
Seller or otherwise materially adversely affect the Seller's ability to perform
its obligations under this Agreement, nor is there any judgment, decree,
injunction, rule or order of any legal or administrative body or arbitrator
outstanding against the Seller or any subsidiary of the Seller having, or which
insofar as reasonably can be foreseen, in the future could have, any such
effect.

     4.10 Taxes and Tax Returns.
          ---------------------

          (a) Except where the failure to do so would not have a Material
     Adverse Effect, the Seller and each of its subsidiaries (referred to for
     purposes of this Section 4.10, collectively, as the "SELLER COMPANIES")
     have, since December 31, 1989, timely filed in correct form all Filed Tax
     Returns.

          (b) The Seller Companies have paid all Taxes shown as being due on the
     Filed Tax Returns.

          (c) No assessment that has not been settled or otherwise resolved has
     been made with respect to Taxes not shown on the Filed Tax Returns, other
     than such additional Taxes as are being contested in good faith and which
     if determined adversely to the Seller Companies would not have a Material
     Adverse Effect. No deficiency in Taxes or other proposed adjustment that
     has not been settled or otherwise resolved has been asserted in writing by
     any taxing authority against any of the Seller Companies, which if
     determined adversely to the Seller Companies would have a Material Adverse
     Effect. No material Tax Return of any of the Seller Companies is now under
     examination by any applicable taxing authority. There are no material liens
     for Taxes (other than current Taxes not yet due and payable) on any of the
     assets of any Seller Company.

          (d) Adequate provision has been made on the Seller Balance Sheet for
     all Taxes of the Seller Companies in respect of all periods through the
     date hereof.

          (e) Except with respect to intra-Seller Company agreements made or
     required under the federal consolidated tax return regulations, none of the
     Seller Companies is a party to or bound by any Tax indemnification, Tax
     allocation or Tax sharing agreement with any person or entity or has any
     current or potential contractual obligation to indemnify any other person
     or entity with respect to Taxes.

          (f) None of the Seller Companies has filed or been included in a
     combined, consolidated or unitary income Tax Return (including any
     consolidated federal income Tax Return) other than one of which one of the
     Seller Companies was the parent.

          (g) None of the Seller Companies has made any payments, is obligated
     to make any payments, or is a party to any agreement that could obligate it
     to make any payments that will not be deductible under Code Section 280G.

     4.11 Employees.
          ---------

          (a) Except as set forth in Section 4.11(a) of the Seller Disclosure
     Schedule, neither the Seller nor any of its subsidiaries maintains or
     contributes to any "employee pension benefit plan", as such term is defined
     in Section 3 of ERISA (the "SELLER PENSION PLANS"), "employee welfare
     benefit plan", as such term is defined in Section 3 of ERISA (the "SELLER
     BENEFIT PLANS"), stock option plan, stock purchase plan, deferred
     compensation plan, other employee benefit plan for employees of the Seller
     or any subsidiary thereof, or any 

                                      A-17

<PAGE>   118

     other plan, program or arrangement of the same or similar nature that
     provides benefits to non-employee directors of the Seller or any subsidiary
     thereof (collectively, the "SELLER OTHER PLANS").

          (b) The Seller shall have delivered to the Buyer within five (5)
     business days after the delivery of the Seller Disclosure Schedule a
     complete and accurate copy of each of the following with respect to each of
     the Seller Pension Plans, the Seller Benefit Plans and the Seller Other
     Plans: (i) plan document; (ii) trust agreement or insurance contract, if
     any; (iii) most recent IRS determination letter, if any; (iv) most recent
     actuarial report, if any; and (v) most recent annual report on Form 5500.

          (c) The value of the assets of each of the Seller Pension Plans
     subject to Title IV of ERISA will exceed as of the Effective Time that
     plan's "Benefit Liabilities" as that term is defined in Section 4001(a)(16)
     of ERISA, when determined under actuarial factors that would apply if that
     plan terminated in accordance with all applicable legal requirements and,
     as of the date hereof, none of such plans are underfunded by any material
     amounts.

          (d) To the best knowledge of the Seller, each of the Seller Pension
     Plans and each of the Seller Benefit Plans has been administered in
     compliance with its terms in all material respects and is in compliance in
     all material respects with the applicable provisions of ERISA (including,
     but not limited to, the funding and prohibited transactions provisions
     thereof), the Code and other applicable laws, except to the extent that
     non-compliance would not have a Material Adverse Effect on the Seller,
     taken as a whole.

          (e) To the best knowledge of the Seller, there has been no reportable
     event within the meaning of Section 4043(b) of ERISA or any waived funding
     deficiency within the meaning of Section 412(d)(3) (or any predecessor
     section) of the Code with respect to any Seller Pension Plan.

          (f) The Seller and its subsidiaries have made or provided for all
     contributions to the Seller Pension Plans required thereunder.

          (g) Other than the contributions to the defined benefit plans
     maintained by the Co-operative Banks Employees Retirement Association
     and/or the Savings Banks Employees Retirement Association, neither the
     Seller nor any of its subsidiaries contributes or has contributed to any
     multiple employer pension plan or to any "Multiemployer Plan," as such term
     is defined in Section 3(37) of ERISA.

          (h) To the best knowledge of the Seller, each of the Seller Pension
     Plans which is intended to be a qualified plan within the meaning of
     Section 401(a) of the Code is so qualified, and the Seller is not aware of
     any fact or circumstance which would adversely affect the qualified status
     of any such plan.

          (i) Except as set forth in Section 4.11(i) of the Seller Disclosure
     Schedule, neither the Seller nor any of its subsidiaries is party to or
     maintains any contract or other arrangement with any employee or group of
     employees, providing severance payments, stock or stock-equivalent payments
     or post-employment benefits of any kind or providing that any otherwise
     disclosed plan, program or arrangement will irrevocably continue, with
     respect to any or all of its participants, for any period of time.

     4.12 AGREEMENTS WITH BANKING AUTHORITIES. Neither the Seller nor any of its
subsidiaries is a party to any commitment, letter (other than letters addressed
to regulated depository institutions generally), written agreement, memorandum
of understanding or order to cease and desist with any federal or state
governmental entity charged with the supervision or regulation of 



                                      A-18
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banks or bank holding companies or engaged in the insurance of bank deposits
which restricts materially the conduct of its business, or in any manner relates
to its capital adequacy, credit policies, management or overall safety and
soundness or such entity's ability to perform its obligations hereunder, and
neither the Seller nor any of its subsidiaries has received written notification
from any such federal or state governmental entity that any such Person may be
requested to enter into, or otherwise be subject to, any such commitment,
letter, written agreement, memorandum of understanding or cease and desist
order.

     4.13 MATERIAL AGREEMENTS. Except as set forth in any of the Seller
Disclosure Schedules or the index of exhibits in the Seller's Annual Report on
Form 10-K for the year ended December 31, 1995, as of the date of this
Agreement, except for this Agreement and the other Transaction Documents,
neither the Seller nor any of its subsidiaries is a party to or is bound by (a)
any agreement, arrangement, or commitment that is material to the financial
condition, results of operations or business of the Seller or any Significant
Subsidiary of the Seller, except those entered into in the ordinary course of
business; (b) any written (or oral, if material) agreement, arrangement, or
commitment relating to the employment of any person or the election or retention
in office or severance of any present or former director or officer of the
Seller or any of its subsidiaries; (c) any contract, agreement, or understanding
with any labor union; (d) any agreement by and among the Seller, its
subsidiaries and/or any Affiliate thereof; or (e) any contract or agreement or
amendment thereto that would be required to be filed as an Exhibit to a Form
10-K filed by the Seller as of the date hereof that has not been filed as an
Exhibit to the Form 10-K filed by it for 1995.

     4.14 OWNERSHIP OF PROPERTY. Section 4.14 of the Seller Disclosure Schedule
sets forth a true and complete list of all real property owned, leased or
operated by the Seller or its subsidiaries (including all of the branches of the
Seller's two subsidiary banks and all of the Seller's properties acquired by
foreclosure proceedings in the ordinary course of business but excluding any
specific listing of any real property carried at nominal value, for which only a
generic description will be included on such schedule) as of the date hereof.
The Seller directly or indirectly through its subsidiaries has good and
marketable title to all assets and properties, whether real or personal,
tangible or intangible, including, without limitation, the capital stock of its
subsidiaries and all other assets and properties reflected in its consolidated
balance sheet as of June 30, 1996, or acquired subsequent thereto subject to no
encumbrances, liens, mortgages, security interests or pledges, except (a) those
items that secure liabilities that are reflected in said balance sheet or the
notes thereto or incurred in the ordinary course of business after the date of
such balance sheet and not otherwise prohibited by the terms hereof, (b)
dispositions for adequate consideration in the ordinary course of business or as
expressly permitted by the terms hereof, (c) statutory liens for amounts not yet
delinquent or which are being contested in good faith, (d) those items that
secure public or statutory obligations or any discount with, borrowing from, or
other obligations to, any Federal Reserve Bank or Federal Home Loan Bank,
inter-bank credit facilities, or any transaction by a subsidiary acting in a
fiduciary capacity, and (e) such encumbrances, liens, mortgages, security
interests, and pledges that are not material in character, amount or extent.
Neither the Seller nor any of its subsidiaries has received any notice of
violation of any applicable zoning or environmental regulation, ordinance or
other law, order, regulation, or requirement relating to its properties, except
as set forth in Section 4.14 of the Seller Disclosure Schedule. The Seller and
its subsidiaries as lessees have the right under valid and existing leases to
occupy, use, possess and control all property leased by the Seller and its
subsidiaries as presently occupied, used, possessed and controlled by the Seller
and its subsidiaries. Neither the Seller nor any of its subsidiaries is in
default, and there has not occurred any event that with the lapse of time or
giving of notice or both would constitute a default, under any leases pursuant
to which the Seller or any of its subsidiaries leases any real property, except
for such defaults which, individually or in the aggregate, would not result in
the forfeiture of the use or occupancy of the property covered by any such lease
or would not result in a material liability to the Seller or any Significant
Subsidiary of the Seller which is not reflected on the consolidated balance
sheet of the Seller dated as of June 30, 1996. All such leases 


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constitute legal, valid and binding obligations of the Seller or its
subsidiaries and, to the knowledge of the Seller, the other party thereto,
enforceable by the Seller or such subsidiary in accordance with their respective
terms, except that enforcement thereof may be limited by the receivership,
conservatorship and supervisory powers of bank regulatory agencies generally as
well as bankruptcy, insolvency, reorganization, moratorium or other similar laws
affecting enforcement of creditors' rights generally and except that enforcement
thereof may be subject to general principles of equity (regardless of whether
enforcement is considered in a proceeding in equity or at law) and the
availability of equitable remedies. Section 4.14 of the Seller Disclosure
Schedule sets forth the expiration date and renewal terms of each such lease.
Neither the Seller nor any of its subsidiaries has received notice of, or made a
claim with respect to, any breach or default under any leases pursuant to which
the Seller or any of its subsidiaries lease any real property.

     4.15 REPORTS. Since January 1, 1993, the Seller and its subsidiaries have
filed, and subsequent to the date hereof will file, all reports, registrations
and statements, together with any amendments required to be made with respect
thereto, that were and are required to be filed with (a) the SEC, including, but
not limited to, Forms 10-K, Forms 10-Q, Forms 8-K and proxy statements (and all
such reports, registrations and statements have been or will be delivered by the
Seller to the Buyer), (b) the Federal Reserve Board, (c) the FDIC, and (d) any
applicable state securities or banking authorities (except, in the case of state
securities authorities, no such representation is made as to filings which are
not material) (all such reports and statements are collectively referred to
herein as the "SELLER REPORTS"). As of their respective dates, the Seller
Reports complied and, with respect to filings made after the date of this
Agreement, will at the date of filing comply, in all material respects with all
of the statutes, rules and regulations enforced or promulgated by the regulatory
authority with which they were filed and did not contain and, with respect to
filings made after the date of this Agreement, will not at the date of filing
contain, any untrue statement of a material fact or omit to state a material
fact required to be stated therein or necessary in order to make the statements
therein, in light of the circumstances under which they were made, not
misleading.

     4.16 COMPLIANCE WITH APPLICABLE LAW. Each of the Seller and each
Significant Subsidiary thereof holds all licenses, franchises, permits and
authorizations necessary for the lawful conduct of its business, and each of the
Seller and each Significant Subsidiary thereof has complied with and is not in
violation of or default in any respect under any, applicable law, statute,
order, rule, regulation or policy of, or agreement with, any federal, state or
local governmental agency or authority relating to the Seller or such
Significant Subsidiary (other than where such default or noncompliance will not
result in, or create the possibility of resulting in, a material limitation on
the conduct of the business of the Seller, will not cause, or create the
possibility of causing, the Seller or any Significant Subsidiary thereof to
incur any financial penalty in excess of $20,000 (including but not limited to
any civil money penalty or other monetary sanction under Section 8(i)(2) of the
FDIA, 12 U.S.C. [Section]1818(i)(2), or under any applicable state law
("CMPs")), and will not otherwise result, or create the possibility of resulting
in any Material Adverse Effect on the Seller or any Significant Subsidiary of
the Seller), and neither the Seller nor any Significant Subsidiary of the Seller
has received any notice of any violation of any such law, statute, order, rule,
regulation, policy or agreement, or the commencement of any proceeding in
connection with any such violation (including but not limited to any hearing or
investigation relating to the imposition or contemplated imposition of CMPs),
and does not know of any violation of, any such law, statute, order, rule,
regulation, policy or agreement which would have such a result.

     4.17 Environmental Matters.
          ---------------------

          (a) Except as set forth in Section 4.17(a) of the Seller Disclosure
     Schedule, the Seller, each of its Significant Subsidiaries and the
     Participation Facilities (as such term is hereinafter defined) are and have
     been in material compliance with all applicable laws, 

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<PAGE>   121

     rules, regulations, standards and requirements of the EPA and of state and
     local agencies with jurisdiction over pollution or protection of the
     environment.

          (b) Except as set forth in Section 4.17(b) of the Seller Disclosure
     Schedule, there is no suit, claim, action or proceeding now pending or, to
     the best knowledge of the Seller, threatened, before any court,
     governmental agency or board or other forum in which the Seller, any of its
     Significant Subsidiaries or any Participation Facility has been or, with
     respect to threatened proceedings, may be, named as a defendant (i) for
     alleged noncompliance (including by any predecessor), with any
     environmental law, rule or regulation or (ii) relating to the release into
     the environment of any Hazardous Material (as hereinafter defined) whether
     or not occurring at or on a site owned, leased or operated by the Seller,
     any of its Significant Subsidiaries or any Participation Facility.

          (c) Except as set forth in Section 4.17(c) of the Seller Disclosure
     Schedule, to the best knowledge of the Seller, there is no suit, claim,
     action or proceeding pending, or threatened, before any court, governmental
     agency or board or other forum in which any Loan Property has been or, with
     respect to threatened proceedings, may be, named as a defendant or involved
     (i) for alleged noncompliance (including by any predecessor) with any
     environmental law, rule or regulation or (ii) relating to the release into
     the environment of any Hazardous Material whether or not occurring at or on
     a site owned, leased, operated or involving a Loan Property.

          (d) Except as set forth in Sections 4.17(a), (b) and (c) of the Seller
     Disclosure Schedule, to the best knowledge of the Seller's management,
     there is no reasonable basis for any suit, claim, action or proceeding as
     described in subsection (b) or (c) of this Section 4.17.

          (e) Except as set forth in Section 4.17(e) of the Seller Disclosure
     Schedule, during and, to the best knowledge of the Seller, prior to the
     period of (i) the ownership or operation by the Seller or any of its
     Significant Subsidiaries of any of their current properties, or (ii) the
     participation by the Seller or any of its Significant Subsidiaries in the
     management of any Participation Facility, there has been no release of
     Hazardous Material in, on, under or affecting such properties, that would
     subject the Seller or such Significant Subsidiary to any liability which
     would result in a Material Adverse Effect with respect to the Seller or
     such Significant Subsidiary. Except as set forth in Section 4.17(e) of the
     Seller Disclosure Schedule, to the best knowledge of the Seller, none of
     the branch offices of any subsidiary or any other real property owned,
     operated or leased by the Seller was at any time the site of any gas
     station, manufacturing plant or industrial business or activity or was at
     any time a site on which any Hazardous Material, was stored, produced or
     otherwise located.

          (f) The Seller and its Significant Subsidiaries have asked for
     representations from borrowers and/or have conducted due diligence with
     respect to each of the Loan Properties in a manner consistent with industry
     practice at the time the loan was granted for secured loan transactions of
     the size and type of the loan for which such Loan Property was granted as
     security, and in the course thereof, or subsequent thereto, nothing has
     come to the attention of the Seller or any of its Significant Subsidiaries
     which could be reasonably likely to prevent the Seller or such Significant
     Subsidiary from exercising its right to foreclose on its security interest
     therein.

          (g) None of the disclosures set forth in Section 4.17 of the Seller
     Disclosure Schedule is reasonably likely to result in the closure of any of
     the branch offices of any of the Significant Subsidiaries of the Seller or
     in a Material Adverse Effect with respect to the Seller or any Significant
     Subsidiary.

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<PAGE>   122

          (h) The transactions contemplated herein are not subject to the
     provisions of any applicable environmental restrictive transfer law.

          (i) The following definitions apply for purposes of this Section 4.17:
     (i) "LOAN PROPERTY" means any property in which the Seller or any of its
     Significant Subsidiaries holds a security interest, and, where required by
     the context, said term means the owner or operator of such property; (ii)
     "PARTICIPATION FACILITY" means any facility in which the Seller or any of
     its Significant Subsidiaries participates in the management and, where
     required by the context, said term means the owner or operator of such
     property; (iii) "HAZARDOUS MATERIAL" means any pollutant, contaminant,
     hazardous material, hazardous waste, or hazardous substance as defined
     under the Comprehensive Environmental Response, Compensation, and Liability
     Act, 42 U.S.C. [Section]9601 ET SEQ., or the Resource Conservation and
     Recovery Act, 42 U.S.C. [Sections]6901 ET SEQ., the Clear Water Act, 33
     U.S.C. [Section]1321, ET SEQ., or any other federal, state or local law
     relating to safety, health, or environmental protection or any regulations
     promulgated under any of the foregoing, and specifically includes oil and
     any other petroleum derived products, asbestos, polychlorinated biphenyls
     (PCB's) and, with respect to any residential property, lead paint and
     radon.

     4.18 CHAPTERS 110D AND 110F NOT APPLICABLE. The provisions of Chapters 110D
and 110F of the Massachusetts General Laws will not, prior to the termination of
this Agreement, assuming the accuracy of the representations contained in
Section 3.12 hereof (without giving effect to the knowledge qualification
thereof), apply to this Agreement or any of the other Transaction Documents or
any of the transactions contemplated hereby or thereby.

     4.19 OWNERSHIP OF BUYER COMMON STOCK. As of the date hereof, neither the
Seller nor, to its best knowledge, any of its affiliates or associates (as such
terms are defined under the Exchange Act), (a) beneficially own, directly or
indirectly, or (b) are parties to any agreement, arrangement or understanding
for the purpose of acquiring, holding, voting or disposing of, in each case,
shares of capital stock of the Buyer, which in the aggregate represent five
percent (5%) or more of the outstanding shares of capital stock of the Buyer
entitled to vote generally in the election of directors (other than Trust
Account Shares).

     4.20 INSURANCE. The Seller and each of its subsidiaries is presently
insured, and since January 1, 1996 has been insured, for reasonable amounts
against such risks as companies engaged in a similar business in a similar
location would, in accordance with good business practice, customarily be
insured. The Seller has made available to the Buyer copies of policies relating
to insurance maintained by the Seller or its subsidiaries with respect to their
properties and the conduct of their respective businesses.

     4.21 LABOR. No work stoppage involving the Seller or any of its
subsidiaries is pending or, to the best knowledge of the Seller's management,
threatened. Neither the Seller nor any of its subsidiaries is involved in, or,
to the best knowledge of the Seller's management, threatened with or affected
by, any dispute, arbitration, lawsuit or administrative proceeding relating to
labor or employment matters which might reasonably be expected to result in a
Material Adverse Effect with respect to the Seller or any of its Significant
Subsidiaries. No employees of the Seller or any of its subsidiaries are
represented by any labor union, and, to the best knowledge of the Seller's
management, no labor union is attempting to organize employees of the Seller or
any of its subsidiaries.

     4.22 MATERIAL INTERESTS OF CERTAIN PERSONS. Except as disclosed in Section
4.22 of the Seller Disclosure Schedule, no officer or director of the Seller, or
any "associate" (as such term is defined in Rule 14a-1 under the Exchange Act)
of any such officer or director, has any material interest in any material
contract or property (real or personal), tangible or intangible, used in or
pertaining to the business of the Seller or any of its subsidiaries.

    
                                      A-22
<PAGE>   123

     4.23 ABSENCE OF REGISTRATION OBLIGATIONS. Neither the Seller nor any of its
subsidiaries is under any obligation, contingent or otherwise, by reason of any
agreement to register any of its securities under the Securities Act which will
survive the Merger.

     4.24 LOANS. All currently outstanding loans of, or current extensions of
credit by, the Seller or any of its Significant Subsidiaries (individually, a
"LOAN," and collectively, the "LOANS") were solicited, originated and currently
exist in material compliance with all applicable requirements of federal and
state law and regulations promulgated thereunder and applicable loan policies of
the Person extending the same, except for such changes to the circumstances of
the obligor thereunder or the collateral occurring subsequent to the origination
thereof and over which the Seller or such subsidiary had no control. The Loans
are adequately documented and, to the best knowledge of the Seller, each note
evidencing a Loan or loan or credit agreement or security instrument related to
the Loans constitutes a valid, legal and binding obligation of the obligor
thereunder, enforceable in accordance with the terms thereof, except where the
failure thereof, individually or in the aggregate, would not have a Material
Adverse Effect with respect to the Seller or any of its Significant
Subsidiaries. There are no oral modifications or amendments or additional
agreements related to the Loans that are not reflected in the records of the
Seller or such subsidiary, and no claims of defense as to the enforcement of any
Loan has been asserted and the Seller is aware of no acts or omissions which
would give rise to any claim or right of rescission, set-off, counterclaim or
defense, except where such would not have, either individually or in the
aggregate, a Material Adverse Effect with respect to the Seller or any of its
Significant Subsidiaries. The Seller and its Significant Subsidiaries currently
maintain, and shall continue to maintain, an allowance for loan losses allocable
to the Loans which is adequate to provide for all known and reasonably estimable
losses, net of any recoveries relating to such extensions of credit previously
charged off, on the Loans, such allowance for loan losses complying in all
material respects with all applicable loan loss reserve requirements established
in accordance with GAAP and by any governmental authorities having jurisdiction
with respect to the Seller or any such subsidiary. Except as set forth in
Section 4.24 of the Seller Disclosure Schedule, none of the Loans are presently
serviced by third parties and, other than pursuant to obligations in accordance
with sales contracts entered into in the ordinary course of business and
consistent with past practice, there is no obligation which could result in any
Loan becoming subject to any third party servicing.

     4.25 CAPITALIZATION. As of the date hereof, without giving effect to the
transactions contemplated hereby, the subsidiaries of the Seller which are
"insured depository institutions" (a) are "well capitalized", as defined in the
FDIA, and (b) meet all capital requirements, standards and ratios required by
each state or federal bank regulator with jurisdiction over such Persons. No
such regulator has indicated that it will condition any of the regulatory
approvals upon an increase in any such Person's capital or compliance with any
special capital requirement, standard or ratio.

     4.26 CRA RATING. Each subsidiary of the Seller which is an "insured
depository institution" was rated "Satisfactory" or better following its most
recent Community Reinvestment Act examination by the regulatory agency
responsible for its supervision. Neither the Seller nor any of such subsidiaries
has received any notice of and none of such Persons has any knowledge of any
planned or threatened objection by any community group to the transactions
contemplated hereby.

     4.27 SELLER INFORMATION. The information relating to the Seller and its
subsidiaries to be contained in the Joint Proxy Statement as described in
Section 5.04 hereof, and any other documents filed with the SEC or any
regulatory agency in connection herewith, to the extent such information is
provided in writing by the Seller, will not contain any untrue statement of a
material fact or omit to state a material fact necessary to make such
information not misleading.

     4.28 DISCLOSURE. No representation or warranty contained in this Agreement,
and no statement contained in any certificate, list or other writing, including
but not necessarily limited to the Seller Disclosure Schedule, furnished to the
Buyer pursuant to the provisions hereof, to the best 


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<PAGE>   124

knowledge of the Seller, contains or will contain any untrue statement of a
material fact or omits to state a material fact necessary in order to make the
statements herein or therein not misleading. To the best knowledge of the
Seller, all information material to the Merger and the transactions contemplated
by this Agreement, or which is necessary to make the representations and
warranties herein contained not misleading, has been disclosed in writing to the
Buyer.

                                    ARTICLE V

                            COVENANTS OF THE PARTIES
                            ------------------------

     5.01 CONDUCT OF THE BUSINESS OF SELLER. During the period from the date of
this Agreement to the earlier of the Effective Time or the date of termination
of this Agreement, the Seller:

          (a) shall, and shall cause each of its subsidiaries to, conduct its
     business and engage in transactions only in the ordinary and usual course
     of business consistent with past practices, which shall mean (i) conducting
     its banking and other business in the ordinary and usual course, (ii)
     refraining from any of the activities described in Section 5.01(b) below,
     (iii) not entering into any material transactions except in the ordinary
     and usual course of business consistent with past practices and (iv)
     complying with the following covenants:

          (A) maintaining its corporate existence and good standing, except
     where any failure to maintain such good standing does not or would not have
     a Material Adverse Effect on the Seller or any of its Significant
     Subsidiaries;

          (B) using all reasonable efforts to maintain and keep its properties
     in as good repair and condition in all material respects as they presently
     exist, except for ordinary wear and tear and damage due to casualty;

          (C) using all reasonable efforts to maintain in full force and effect
     insurance generally comparable in amount and in scope of coverage to that
     now maintained by it;

          (D) complying with and performing in all material respects its
     obligations and duties (y) under contracts, leases and documents relating
     to or affecting its assets, properties and business and (z) imposed upon it
     by all federal, state and local laws and all rules, regulations and orders
     imposed by federal, state or local governmental authorities, judicial
     orders, judgments, decrees and similar determinations; and

          (E) using all reasonable efforts to preserve its business organization
     intact and the goodwill of those having business relationships with the
     Seller or any of the Seller's subsidiaries, to keep available the services
     of its officers and employees as a group and to maintain satisfactory
     relationships with borrowers, depositors, other customers and others having
     business relationships with it;

          (b) shall not, and shall not permit any of its subsidiaries to,
     without the prior written consent of the Buyer:

               (i) engage or participate in any material transaction or incur or
          sustain any material obligation or liability except in the ordinary,
          regular and usual course of its businesses consistent with past
          practices;

               (ii) offer an interest rate with respect to any deposit that
          would constitute such deposit a "brokered deposit" under 12 C.F.R.
          [Section]337.6(a)(l)(ii);


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<PAGE>   125

               (iii) except in the ordinary, regular and usual course of
          business consistent with past practices, sell, lease, transfer,
          assign, encumber or otherwise dispose of or enter into any contract,
          agreement or understanding to lease, transfer, assign, encumber or
          dispose of any of its assets; PROVIDED that the Seller and its
          subsidiaries may (A) sell the four automobiles more specifically
          described in Section 5.01(b)(iii) of the Seller Disclosure Schedule to
          the employees currently using the same in the performance of their
          duties with the Seller and/or such subsidiaries at a purchase price
          equal to the depreciated value thereof reflected on the Seller's or
          such subsidiary's books and records and as otherwise described in said
          Section of the Seller Disclosure Schedule and (B) acquire and dispose
          of loans and investment securities in the ordinary course of business
          consistent with past practice;

               (iv) file any application to open, close or relocate any branch
          office;

               (v) open, close, relocate, or give any notice (written or verbal)
          to customers or governmental authorities or agencies to open, close or
          relocate the operations of any branch office; or

               (vi) waive any material right, whether in equity or at law, that
          it has with respect to any asset except in the ordinary, regular and
          usual course of business consistent with past practice;

          (c) shall, at the Buyer's request and expense, use its best efforts to
     cooperate with the Buyer with respect to preparation for the combination
     and integration as of the Effective Time of the businesses, systems and
     operations of the Buyer and the Seller, and shall confer on a regular and
     frequent basis with one or more representatives of the Buyer to report on
     operational and related matters;

          (d) shall not declare or pay any dividends on or make any other
     distributions in respect of Seller Common Stock, except for regular
     quarterly cash dividends on Seller Common Stock at a rate not in excess of
     the Seller's current dividend rate and subject to the terms of Section 5.19
     hereof;

          (e) shall not adopt or amend (other than amendments required by
     applicable law or amendments that reduce amounts payable by it or its
     subsidiaries) in any material respect any Seller Pension Plan, any Seller
     Benefit Plan or any Seller Other Plan or enter (or permit any of its
     subsidiaries to enter) into any employment, retention, severance or similar
     contract with any person (including, without limitation, contracts with
     management which might require that payments be made upon the consummation
     of the transactions contemplated hereby) or amend any such existing
     agreements, plans or contracts to increase any amounts payable thereunder
     or benefits provided thereunder, or grant or permit any increase in
     compensation to its or its subsidiaries' employees as a class or pay any
     bonus except (i) as previously determined and consistent with the terms of
     the Seller's short term incentive plans, the Seller may pay bonuses to its
     employees under and in accordance with the provisions of such short term
     incentive plans, PROVIDED that such bonuses do not exceed the amount set
     forth in Section 5.01(e)(i) of the Seller Disclosure Schedule, and (ii) as
     otherwise set forth in Section 5.01(e)(ii) of the Seller Disclosure
     Schedule provided that with respect to this clause (ii) such bonuses and
     increases are made in the ordinary course of business in accordance with
     past practice;

          (f) except as permitted in Section 5.01(b)(iii), shall not, with
     respect to itself or any of its subsidiaries, authorize, recommend, propose
     or announce an intention to authorize, recommend or propose, or enter into
     an agreement with respect to, any merger, consolidation, purchase and
     assumption transaction or business combination (other than the 




                                      A-25
<PAGE>   126

          Merger), any acquisition of a material amount of assets or securities
     or assumption of liabilities (including deposit liabilities), any
     disposition of a material amount of assets or securities, or any release or
     relinquishment of any material contract rights;

          (g) shall not propose or adopt amendments to its or any of its
     subsidiaries' articles of organization or By-Laws;

          (h) shall not issue, deliver or sell any shares (whether original
     issuance or from treasury shares) of its capital stock or securities
     convertible into or exercisable for shares of its capital stock (or permit
     any of its subsidiaries to issue, deliver or sell any shares of such
     subsidiaries' capital stock or securities convertible into or exercisable
     for shares of such subsidiaries' capital stock), except for the sale of up
     to 6,200 shares of Seller Common Stock pursuant to the Seller's 1993
     Employee Stock Purchase Plan and except upon exercise or fulfillment of
     rights or options issued or existing pursuant to employee benefit plans,
     programs or arrangements, dividend reinvestment plans, or the terms of
     convertible securities, all to the extent outstanding or in existence on
     the date hereof, and except upon exercise of the Seller Option, as
     applicable, or effect any stock split, reverse stock split,
     recapitalization, reclassification or similar transaction or otherwise
     change its equity capitalization as it existed on June 30, 1996;

          (i) shall not grant, confer or award any options, warrants, conversion
     rights or other rights, not existing on the date hereof, to acquire any
     shares of its capital stock;

          (j) shall not purchase, redeem or otherwise acquire, or permit any of
     its subsidiaries to purchase, redeem or otherwise acquire, any shares of
     its capital stock or any securities convertible into or exercisable for any
     shares of its capital stock, except in a fiduciary capacity;

          (k) shall not impose, or suffer the imposition, on any share of
     capital stock held by it or by any of its subsidiaries of any material
     lien, charge, or encumbrance, or permit any such lien, charge, or
     encumbrance to exist;

          (l) shall not incur, or permit any of its subsidiaries to incur, any
     additional debt obligation or other obligation for borrowed money, or to
     guaranty any additional debt obligation or other obligation for borrowed
     money, except in the ordinary course of business consistent with past
     practices, which shall include but not necessarily be limited to creation
     of deposit liabilities, Federal Home Loan Bank advances, purchases of
     federal funds, sales of certificates of deposit and entry into repurchase
     agreements or other similar arrangements commonly employed by banks;

          (m) shall not incur or commit to any capital expenditures or any
     obligations or liabilities in connection therewith, other than capital
     expenditures and such related obligations or liabilities incurred or
     committed to in the ordinary and usual course of business consistent with
     past practices, and, in all cases, the Seller agrees to consult with the
     Buyer with respect to capital expenditures that individually exceed $75,000
     or cumulatively exceed $300,000;

          (n) shall use all reasonable efforts to improve its business, results
     of operations, financial condition and prospects;

          (o) shall not, except as expressly contemplated hereby, enter into any
     contract with any Affiliate;


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<PAGE>   127

          (p) shall not, except for transactions in the ordinary course of
     business consistent with past practice, enter into or terminate any
     material contract or agreement, or make any changes in any of its material
     leases or contracts, other than renewals of contracts for less than a two
     (2) year period and, subject to the provisions of Section 5.18 hereof,
     leases without material adverse change of terms;

          (q) shall not, other than in prior consultation with the other party
     to this Agreement or except in the ordinary course of business and
     consistent with past practice, restructure or materially change its
     investment securities portfolio or its "gap position" through purchases,
     sales or otherwise, or the manner in which the portfolio is classified or
     reported;

          (r) shall not agree, in writing or otherwise, to take any of the
     foregoing actions or any action which would make any of its representations
     or warranties contained herein untrue or incorrect in any material respect.

     5.02 Access to Properties and Records; Confidentiality.
          -------------------------------------------------

          (a) The Seller shall permit the Buyer reasonable access to its
     properties and those of its subsidiaries, and shall disclose and make
     available to the Buyer all Records, including all books, papers and records
     relating to the assets, stock ownership, properties, operations,
     obligations and liabilities of the Seller and its subsidiaries, including,
     but not limited to, all books of account (including the general ledger),
     tax records, minute books of directors and stockholders meetings,
     organizational documents, By-Laws, material contracts and agreements,
     filings with any regulatory authority, accountants' work papers (to the
     extent consent from such accountants is obtained), litigation files, plans
     affecting employees, and any other business activities or prospects in
     which the Buyer may reasonably have an interest in light of the
     transactions contemplated hereby. The Seller shall make arrangements with
     each third party provider of services to the Seller to permit the Buyer
     reasonable access to all of the Seller's Records held by each such third
     party. The Buyer shall permit the Seller reasonable access to such
     properties and records of the Buyer and/or its subsidiaries in which the
     Seller may reasonably have an interest in light of the transactions
     contemplated hereby. Neither the Buyer nor the Seller nor any of their
     respective subsidiaries shall be required to provide access to or to
     disclose information where such access or disclosure would violate or
     prejudice the rights of any customer, would jeopardize the attorney-client
     privilege of the institution in possession or control of such information,
     or would contravene any law, rule, regulation, order, judgment, decree or
     binding agreement or, in the event of any litigation or threatened
     litigation between the parties over the terms of this Agreement where
     access to information may be adverse to the interests of such party. The
     parties will use all reasonable efforts to make appropriate substitute
     disclosure arrangements under circumstances in which the restrictions of
     the preceding sentence apply.

          (b) All Confidential Information furnished by each party hereto to the
     other, or to any of its affiliates, directors, officers, employees,
     representatives or agents (such persons being collectively referred to
     herein as "REPRESENTATIVES"), shall be treated as the sole property of the
     party furnishing the information until consummation of the transactions
     contemplated hereby, and, if such transactions shall not occur, the party
     receiving the information, or any of its affiliates or Representatives, as
     the case may be, shall return to the party which furnished such information
     all documents or other materials containing, reflecting or referring to
     such information, shall keep confidential all such information for the
     period hereinafter referred to, and shall not directly or indirectly at any
     time use such information for any competitive or other commercial purpose;
     PROVIDED, HOWEVER, that the Buyer and its affiliates shall be permitted to
     retain and share with their regulators, 





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<PAGE>   128
     examiners and auditors (who need to know such information and are informed
     of the confidential nature thereof and directed to treat such information
     confidentially) such materials, files and information relating to or
     constituting the Buyer's or any of its affiliate's or Representatives' work
     product, presentations or evaluation materials as the Buyer deems
     reasonably necessary or advisable in connection with auditing or
     examination purposes. The obligation to keep such information confidential
     shall continue for two (2) years from the date this Agreement is
     terminated. In the event that either party or its affiliates or
     Representatives are requested or required in the context of a litigation,
     governmental, judicial or regulatory investigation or other similar
     proceeding (by oral questions, interrogatories, requests for information or
     documents, subpoenas, civil investigative demands or similar process) to
     disclose any Confidential Information, the party or its affiliate or its
     Representative so requested or required will directly or through the party
     of such affiliate or Representative, if practicable and legally permitted,
     prior to providing such information, and as promptly as practicable after
     receiving such request, provide the other party with notice of each such
     request or requirement so that the other party may seek an appropriate
     protective order or other remedy or, if appropriate, waive compliance with
     the provisions of this Agreement. If, in the absence of a protective order
     or the receipt of a waiver hereunder, the party or affiliate or
     Representative so requested or required is, in the written opinion of its
     counsel, legally required to disclose Confidential Information to any
     tribunal, governmental or regulatory authority, or similar body, the party
     or affiliate or Representative so required may disclose that portion of the
     Confidential Information which it is advised in writing by such counsel it
     is legally required to so disclose to such tribunal or authority or similar
     body without liability to the other party hereto for such disclosure. The
     parties and their affiliates and Representatives will exercise reasonable
     efforts to obtain assurance that confidential treatment will be accorded
     the information so disclosed.

     As used in this Section 5.02(b), "CONFIDENTIAL INFORMATION" means all data,
reports, interpretations, forecasts and records (whether in written form,
electronically stored or otherwise) containing or otherwise reflecting
information concerning the disclosing party or its affiliates which is not
available to the general public and which the disclosing party or any affiliate
or any of their respective Representatives provides or has previously provided
to the receiving party or to the receiving party's affiliates or Representatives
at any time in connection with the transactions contemplated by this Agreement,
including but not limited to any information obtained by meeting with
Representatives of the disclosing party or its affiliates, together with
summaries, analyses, extracts, compilations, studies, personal notes or other
documents or records, whether prepared by the receiving party or others, which
contain or otherwise reflect such information. Notwithstanding the foregoing,
the following information will not constitute "CONFIDENTIAL INFORMATION": (i)
information that is or becomes generally available to the public other than as a
result of a disclosure by the receiving party or any affiliate or Representative
of the receiving party, (ii) information that was previously known to the
receiving party or its affiliates or Representatives on a nonconfidential basis
prior to its disclosure by the disclosing party, its affiliates or
Representatives, (iii) information that became or becomes available to the
receiving party or any affiliate or Representative thereof on a nonconfidential
basis from a source other than the disclosing party or any affiliate or
Representatives of the disclosing party, provided that such source is not known
by the disclosing party or its affiliates or Representatives to be subject to
any confidentiality agreement or other legal restriction on disclosing such
information and (iv) information that has been independently acquired or
developed by the receiving party or its affiliates or Representatives without
violating the obligation's of this Section 5.02(b).

     5.03 NO SOLICITATION. Unless and until this Agreement shall have been
properly terminated by either party pursuant to Section 8.01 hereof, neither the
Seller nor any of its subsidiaries shall (and the Seller and each of its
subsidiaries shall use its best efforts to cause its Representatives, including,
but not limited to, investment bankers, attorneys and accountants, not to),
directly or indirectly, encourage, solicit, initiate or participate in any
discussions or negotiations

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with, or, subject to the fiduciary obligations of the Seller's Board of
Directors (as determined in good faith in consultation with outside counsel),
provide any information to, any corporation, partnership, person or other entity
or group (other than the Buyer and its affiliates or Representatives) concerning
any merger, tender offer, sale of substantial assets, sale of shares of capital
stock or debt securities or similar transaction involving the Seller or any of
its subsidiaries (an "ACQUISITION TRANSACTION"), PROVIDED that in accordance
with the fiduciary obligations of the Seller's Board of Directors, the Seller
may participate in discussions in the event that the Seller did not solicit or
initiate such discussions with respect to Acquisition Transactions.
Notwithstanding the foregoing, nothing contained in this Section 5.03 shall
prohibit the Seller or its Board of Directors from taking and disclosing to the
Seller's stockholders a position with respect to a tender offer by a third party
pursuant to Rules 14d-9 and 14e-2(a) promulgated under the Exchange Act or from
making such disclosure to the Seller's stockholders which, in the judgment of
the Board of Directors determined in good faith in consultation with outside
counsel, may be required under applicable law. The Seller will immediately
communicate to the Buyer the terms of any proposal, discussion, negotiation or
inquiry relating to an Acquisition Transaction and the identity of the party
making such proposal or inquiry which it may receive in respect of any such
transaction (which shall mean that any such communication shall be delivered no
less promptly than by telephone within 24 hours of the Seller's receipt of any
such proposal or inquiry) or its receipt of any request for information from the
Federal Reserve Board, the DOJ, or any other governmental agency or authority
with respect to a proposed Acquisition Transaction.

     5.04 Regulatory Matters; Consents.
          ----------------------------

          (a) The Buyer and the Seller shall cooperate in the prompt preparation
     and filing with the SEC of a joint proxy statement in definitive form
     relating to the meetings of the Buyer's and the Seller's stockholders to be
     held in connection with this Agreement and the transactions contemplated
     hereby (the "JOINT PROXY STATEMENT") and the Buyer shall promptly prepare
     and file with the SEC a registration statement on Form S-4 (the "S-4") in
     which the Joint Proxy Statement will be included as a prospectus. Each of
     the Buyer and the Seller shall use all reasonable efforts to have the S-4
     declared effective under the Securities Act as promptly as practicable
     after such filing, and the Buyer and the Seller shall thereafter mail the
     Joint Proxy Statement to their respective stockholders. The Buyer shall
     also use all reasonable efforts to obtain all necessary state securities
     law or "Blue Sky" permits and approvals required to carry out the
     transactions contemplated by this Agreement, and the Buyer and the Seller
     shall each furnish to the other all information concerning itself and the
     holders of its Common Stock as may be reasonably requested in connection
     with any such action.

          (b) The Seller and the Buyer shall have the right to review in
     advance, and to the extent practicable each will consult the other on, in
     each case subject to applicable laws relating to the exchange of
     information, all the information relating to the Seller or the Buyer, as
     the case may be, and any of their respective subsidiaries, which appear in
     any filing made with, or written materials submitted to, any third party or
     any government regulatory body, department, agency or authority in
     connection with the transactions contemplated by this Agreement. In
     exercising the foregoing right, each of the parties hereto shall act
     reasonably and as promptly as practicable. The parties hereto agree that
     they will consult with each other with respect to the obtaining of all
     permits, consents, approvals and authorizations of all third parties and
     government regulatory bodies, departments, agencies or authorities
     necessary or advisable to consummate the transactions contemplated by this
     Agreement, and each party will keep the other apprised of the status of
     matters relating to completion of the transactions contemplated herein.

          (c) The Buyer and the Seller shall, upon request, furnish each other
     with all information concerning themselves, their subsidiaries, directors,
     officers and stockholders

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     and such other matters as may be reasonably necessary or advisable in
     connection with the Joint Proxy Statement, the S-4 or any other statement,
     filing, notice or application made by or on behalf of the Buyer, the Seller
     or any of their respective subsidiaries to any governmental regulatory
     body, department, agency or authority in connection with the Merger and the
     other transactions contemplated by this Agreement.

          (d) The Seller and the Buyer shall promptly advise each other upon
     receiving any communication from any government regulatory body,
     department, agency or authority whose consent or approval is required for
     consummation of the transactions contemplated by this Agreement which
     causes such party to believe that there is a reasonable likelihood that
     such requisite approval will not be obtained or that the receipt of such
     approval will be materially delayed.

          (e) Each of the Seller and the Buyer will cooperate with the other and
     use all reasonable efforts to prepare all necessary documentation, to
     obtain all necessary permits, consents, approvals and authorizations of all
     third parties and governmental bodies necessary to consummate the
     transactions contemplated by this Agreement.

          (f) The Buyer shall prepare and file as soon as practicable and the
     Seller shall cooperate in the preparation and, where appropriate, filing
     of, applications requesting the Consents (as contemplated in Section
     6.01(b) herein), from all required governmental or regulatory authorities
     or agencies. The Buyer shall provide the Seller and its counsel with copies
     of such applications for comment prior to the filing thereof. The parties
     shall immediately upon receipt deliver to each other copies of all filings,
     correspondence and orders to and from such governmental or regulatory
     authorities or agencies transmitted or received in connection with the
     transactions contemplated hereby.

     5.05 APPROVAL OF STOCKHOLDERS. Each party hereto will (a) as promptly as
practicable, take all steps necessary to duly call, give notice of, convene and
hold a meeting of its stockholders for the purpose of approving this Agreement
and the Merger, and for such other purposes as may be necessary or desirable,
(b) recommend to its stockholders the approval of the aforementioned matters to
be submitted by it to its stockholders (subject to compliance with their
fiduciary duties as determined in good faith in consultation with outside
counsel), and (c) cooperate and consult with the other with respect to each of
the foregoing matters.

     5.06 AGREEMENTS OF AFFILIATES; PUBLICATION OF COMBINED FINANCIAL RESULTS.
(a) The Seller shall identify in a letter to the Buyer, after consultation with
counsel, all Persons who, at the time of the meeting of its stockholders
referred to in Section 5.05 hereof, it believes may be deemed to be "affiliates"
of the Seller, as that term is defined for purposes of paragraphs (c) and (d) of
Rule 145 under the Securities Act and SEC accounting Rules 130 and 135 (the
"SELLER AFFILIATES"). The Seller shall use all reasonable efforts to cause each
Person who is identified as a Seller Affiliate in the letter referred to above
to deliver to the Buyer at least forty (40) days prior to the Effective Time an
executed copy of the Seller Affiliates Agreement. Prior to the Effective Time,
the Seller shall amend and supplement such letter and use all reasonable efforts
to cause each additional person who is identified as a Seller Affiliate to
execute a copy of the Seller Affiliates Agreement. Within thirty (30) days after
the end of the first fiscal quarter of the Buyer ending at least thirty (30)
days after the Effective Time, the Buyer will publish results including at least
thirty (30) days of combined operations of the Buyer and the Seller as referred
to in the Seller Affiliates Letter.

     (b) The Buyer shall identify in a letter to the Seller, after consultation
with counsel, all Persons who, at the time of the meeting of its stockholders
referred to in Section 5.05 hereof, it believes may be deemed to be "affiliates"
of the Buyer, as that term is defined for purposes of SEC accounting Rules 130
and 135 (the "BUYER AFFILIATES"). The Buyer shall use all reasonable efforts to
cause each Person who is identified as a Buyer Affiliate in the letter referred
to above to deliver to 


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the Seller at least forty (40) days prior to the Effective Time an executed copy
of the Buyer Affiliates Agreement. Prior to the Effective Time, the Buyer shall
amend and supplement such letter and use all reasonable efforts to cause each
additional person who is identified as a Buyer Affiliate to execute a copy of
the Buyer Affiliates Agreement.

     (c) The Buyer shall use its best efforts to publish, no later than thirty
(30) days after the end of the first month after the Effective Time in which
there are at least thirty (30) days of post-Merger combined operations (which
month may be the month in which the Effective Time occurs), combined sales and
net income figures as contemplated by and in accordance with the terms of SEC
Accounting Series Release No. 135.

     5.07 FURTHER ASSURANCES. Subject to the terms and conditions herein
provided, each of the parties hereto agrees to use all reasonable efforts to, as
promptly as practicable, take, or cause to be taken, all action and to do, or
cause to be done, all things necessary, proper or advisable under applicable
laws and regulations to consummate and make effective the transactions
contemplated by this Agreement or to vest the Buyer with full title to all
properties, assets, rights, approvals, immunities and franchises of the Seller.
In case at any time after the Effective Time any further action is necessary or
desirable to carry out the purposes of this Agreement or to vest the Buyer with
full title to all properties, assets, rights, approvals, immunities and
franchises of the Seller, the proper officers and directors of each party to
this Agreement shall take all such necessary action.

     5.08 PUBLIC ANNOUNCEMENTS. From the date of this Agreement to the Closing
Date, neither of the parties hereto shall make or send a Public Announcement
unless the other party shall have first been afforded reasonable opportunity to
review and comment on the text of such Public Announcement prior to the delivery
of the same; PROVIDED, HOWEVER, that nothing in this Section shall prohibit any
party hereto from making any Public Announcement which its legal counsel deems
necessary under law, if it makes a good faith effort to obtain the other party's
comment to the text of the Public Announcement before making it public.

     5.09 POST-CLOSING GOVERNANCE. From and after the Effective Time, the Board
of Directors of the Buyer shall be expanded by three members and Mr. Bradbury
and two additional individuals selected by the Seller and approved of by the
Buyer in its reasonable business judgment prior to the Effective Time, shall be
appointed as directors of the Buyer. The directors selected by the Seller to
serve as directors of the Buyer shall be divided equally among the three classes
of directors of the Seller, with Mr. Bradbury to be appointed to the class of
directors whose term comes up for reelection in the year 2000. Mr. Bradbury
shall be entitled to serve as a member of the Steering Committee of the Buyer
for so long as he serves as a director of the Buyer. At the Effective Time,
subject to the rights of the Buyer as the sole stockholder of the Seller, the
Board of Directors of the Seller shall consist of those persons comprising the
Board of Directors of the Merger Sub prior to the Effective Time each to hold
office in accordance with the articles of organization and By-Laws of the Seller
as from time to time in effect. Further, at the Effective Time the Board of
Directors of the Subsidiaries of the Seller which are depository institutions
shall consist of those directors of such subsidiaries which the Buyer has
selected to serve as directors of such subsidiaries and such additional persons
as shall be designated by the Buyer prior to the Effective Time. In the event
that the subsidiary banks of the Seller are merged with and into the subsidiary
banks of the Buyer, then Mr. Bradbury and those directors of the Buyer who were
selected by the Seller pursuant to the first sentence of this Section 5.09 shall
become directors of the surviving subsidiary bank(s).

     5.10 MERGER SUBSIDIARY. The Buyer has caused or will cause the Merger
Subsidiary to be organized under the laws of The Commonwealth of Massachusetts.
The authorized capital stock of the Merger Subsidiary consists or will consist
of one hundred (100) shares of common stock, $0.01 par value per share, all of
which shares shall be directly owned by the Buyer. The Buyer, as the sole
stockholder of the Merger Subsidiary, will vote all outstanding shares of
capital stock of the Merger Subsidiary in favor of the Plan of Merger and the
Merger and will not vote to modify or rescind, or 


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otherwise permit the modification or rescission of, such vote prior to a
termination of this Agreement in accordance with Section 8.01 hereof.

     5.11 TAX-FREE REORGANIZATION TREATMENT; ACCOUNTING. (a) Neither the Buyer
nor the Seller shall intentionally take or cause to be taken any action, whether
before or after the Effective Time, which would disqualify the Merger as a
"reorganization" within the meaning of Section 368(a) of the Code; PROVIDED,
HOWEVER, that nothing herein shall limit the ability of the Buyer to exercise
its rights under the Seller Option Agreement.

     (b) Neither the Buyer nor the Seller shall intentionally take or cause to
be taken any action, whether before or after the Effective Time, which would
prevent the Merger from qualifying for pooling of interests accounting
treatment.

     5.12 STOCK LISTING. Buyer shall use all reasonable efforts to cause the
shares of Buyer Common Stock to be issued in connection with the Merger to be
approved for listing on the NASDAQ, subject to official notice of issuance, as
of or prior to the Effective Time.

     5.13 Employment and Benefit Matters.
          ------------------------------

          (a) SERVICE CREDIT. In the event that any employee of the Seller or
     its affiliates is transferred to the Buyer or any affiliate of the Buyer
     and becomes a participant in an employee benefit plan, program or
     arrangement maintained by or contributed to by the Buyer or its affiliates
     (any such employee, a "TRANSFERRED EMPLOYEE"), the Buyer shall cause such
     plan, program or arrangement to treat the prior service of such Transferred
     Employee with the Seller or its affiliates as service rendered to the Buyer
     or its affiliate, as the case may be, for purposes of eligibility to
     participate, vesting and eligibility for special benefits under such plan,
     program or arrangement of the Buyer, but not for purposes of benefit
     accrual. The Buyer agrees to provide the Transferred Employees with the
     types and levels of employee benefits maintained by the Buyer for similarly
     situated employees of the Buyer.

          (b) SEVERANCE OBLIGATIONS. For a period of one (1) year after the
     Closing Date, the Buyer will provide Transferred Employees with a severance
     plan with provisions which are at least as favorable in the aggregate to
     any terminating Transferred Employee as the severance plan currently
     maintained by the Seller for such employee. Any employee of the Seller or
     its affiliates who is not a Transferred Employee whose position is
     terminated on or prior to the Effective Time shall be entitled to severance
     benefits in accordance with the severance plan currently maintained by the
     Seller for such employee.

          (c) TERMINATED PLANS. The Buyer shall have no obligation to any
     Transferred Employee under the Seller's 1993 Employee Stock Purchase Plan
     or the Seller's Deferred Compensation Plan, each of which shall be
     terminated by the Seller prior to the Effective Time.

          (d) SEVERANCE AGREEMENTS. As of the Effective Time, the existing
     severance agreements between the Seller and each of Messrs. Bradbury,
     Cushing and Gilles and Ms. Bergemann shall each be terminated and the Buyer
     and the Seller agree that each such person shall, subject to the provisions
     thereof, each be entitled to the payment and benefits determined pursuant
     to Section 1(a) of their respective severance agreements, such payments to
     be made no later than the Effective Time.

     5.14 ACCOUNTANTS' LETTERS. Each of the Buyer and the Seller shall use all
reasonable efforts to cause to be delivered to the other letters from its
respective independent public accountants, respectively dated as of the date on
which the S-4 (or last amendment thereto) shall become effective and dated as of
the Closing Date, relating to the transactions contemplated by this 



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Agreement, and addressed to the other party, in form and substance which is
reasonably satisfactory to the party receiving such letters and customary in
transactions of the nature contemplated hereby.

     5.15. DIRECTORS' AND OFFICERS' INDEMNIFICATION AND INSURANCE. (a) After the
Effective Time, the Buyer shall honor the indemnification provisions for
officers and directors currently set forth in the Articles of Organization (or
charter or other organizational documents) and By-Laws of the Seller and its
subsidiaries with respect to acts and omissions taken prior to the Effective
Time by such officers and directors, but only to the extent permitted by federal
and Massachusetts law and regulations.

     (b) The Buyer shall maintain the Seller's (including its subsidiaries')
existing directors' and officers' liability insurance (the "D&O INSURANCE")
covering persons who are currently covered by the Seller's D&O Insurance for a
period of six (6) years after the Effective Time on terms no less favorable than
those in effect on the date hereof; PROVIDED, HOWEVER, that the Buyer may
substitute therefor policies providing at least comparable coverage and
containing terms and conditions no less favorable than those in effect on the
date hereof.

     5.16 CONVERSION OF SELLER STOCK OPTIONS. At the Effective Time, all rights
with respect to Seller Common Stock pursuant to stock options granted by the
Seller under any currently existing stock option plans of the Seller shall be
converted into corresponding rights to purchase shares of Buyer Common Stock in
accordance with the applicable provisions of the Plan of Merger.

     5.17 MAINTENANCE OF RECORDS. Through the Effective Time, each of the Buyer
and the Seller will maintain the Records in the same manner and with the same
care that the Records have been maintained prior to the execution of this
Agreement. The Buyer may, at its own expense, make such copies of and excerpts
from the Records as it may deem desirable. All Records, whether held by the
Buyer or the Seller, shall be maintained for such periods as are required by
law, unless the parties shall, applicable law permitting, agree in writing to a
different period. From and after the Effective Time, the Buyer shall be solely
responsible for continuing maintenance of such Records.

        5.18 LEASES. The Seller shall use all reasonable efforts to renew or
extend on a month-to-month basis or for such term as requested by the Buyer, any
lease of a branch office of any subsidiary, other lease of real property or
lease relating to furniture, fixtures or equipment that is currently in effect
but that would otherwise expire on or prior to the Effective Time. The Seller
shall not cancel, terminate or take other action that is likely to result in any
cancellation or termination of any such lease without prior written notice to
the Buyer.

        5.19 DIVIDENDS. After the date of this Agreement, each of the Seller and
the Buyer shall coordinate with the other the declaration of any dividends in
respect of Seller Common Stock and Buyer Common Stock and the record dates and
payment dates relating thereto, it being the intention of the parties hereto
that holders of Seller Common Stock or Buyer Common Stock shall not receive two
dividends, or fail to receive one dividend, for any single calendar quarter with
respect to their shares of Seller Common Stock and/or Buyer Common Stock and any
share of Buyer Common Stock any such holder received in exchange therefor in the
Merger.

        5.20 NOTICE OF CHANGE. Each of the parties hereto shall, subject to any
restrictions under applicable law or regulation, promptly notify the other of
any emergency or other change in the normal course of its or its subsidiaries'
businesses or in the operation of its or its subsidiaries' properties and of any
governmental complaints, investigations or hearings (or communications
indicating that the same may be contemplated) if such emergency, change,
complaint, investigation or hearing would be material to the business, results
of operations, financial condition or prospects of such Person on a consolidated
basis or any of its Significant Subsidiaries considered independently. Further,
each party agrees to give written notice promptly to the other party upon
becoming aware of the occurrence or impending occurrence of any event or
circumstance relating to 

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it or any of its subsidiaries which (i) is reasonably likely to have,
individually or in the aggregate, a Material Adverse Effect on it or (ii) would
cause or constitute a material breach of any of its representations, warranties,
or covenants contained herein, and to use its reasonable efforts to prevent or
promptly to remedy the same.

     5.21 CHANGES IN ACCOUNTING. Between the date hereof and the Closing Date,
neither of the parties hereto shall change its methods of accounting as in
effect at December 31, 1995, except as may be required by changes in GAAP or
regulatory accounting requirements, as concurred in by such party's independent
auditors, nor shall they change their respective fiscal years.

     5.22 SEC FILINGS. Each of the parties hereto shall file all reports,
applications and other documents required to be filed by it with the SEC or any
other governmental entity between the date of this Agreement and the Effective
Time and shall make available to the other copies of all such reports promptly
after the same are filed. If financial statements are contained in any such
reports filed with the SEC, such financial statements will fairly present the
consolidated financial position of the entity filing such statements as of the
dates indicated and the consolidated results of operations, changes in
shareholders' equity, and cash flows for the periods then ended in accordance
with GAAP (subject in the case of interim financial statements to normal
recurring year-end adjustments that are not material). As of their respective
dates, such reports filed with the SEC will comply in all material respects with
applicable securities laws and will not contain any untrue statement of a
material fact or omit to state a material fact required to be stated therein or
necessary in order to make the statements therein, in light of the circumstances
under which they were made, not misleading.

     5.23 COVENANTS OF BUYER. From the date of this Agreement until the earlier
of the Effective Time or the date of termination of this Agreement, the Buyer
covenants and agrees that it shall take no action which would (a) materially
adversely affect the ability of any party to obtain any Consents required for
consummation of the transactions contemplated hereby without the imposition of a
condition or restriction of the type referred to in Section 6.02(g) of this
Agreement, (b) materially adversely affect the ability of any party to perform
its covenants and agreements under this Agreement, or (c) result in the Buyer
entering into an agreement with respect to an acquisition proposed with a third
party which would result in the Merger not being consummated.

     5.24 REGULATORY REPORTS. Each party and its subsidiaries shall file all
reports required to be filed by it with regulatory authorities between the date
of this Agreement and the Effective Time and, to the extent permitted by law,
shall deliver to the other party copies of all such reports promptly after the
same are filed.

     5.25 REGISTRATION OF SHARES. On or prior to the Effective Time, the Buyer
shall file a registration statement on Form S-3 or Form S-8, as the case may be
(or any successor or other appropriate form), with respect to the shares of
Buyer Common Stock subject to the stock options of the Seller to be assumed by
the Buyer pursuant to Section 2.04 of the Plan of Merger and the Buyer shall use
its reasonable efforts to maintain the effectiveness of such registration
statement (and maintain the current status of the prospectus or prospectuses
contained therein) for so long as such options remain outstanding.

     5.26 ENVIRONMENTAL REMEDIATION. With respect to 97 Lowell Road, Concord,
Massachusetts, the Seller will (a) cause the removal of the underground storage
tank that was found to be leaking in 1996, (b) cause a "tightness test" to be
performed upon the other underground storage tank(s) on the premises, and if any
such tanks fail the tightness test, remove such tanks in accordance with
applicable law, (c) test the area surrounding the tanks for the presence of
contaminants and (d) in the event that contamination is found to be present, the
Seller shall effect such remediation as the Buyer shall request in writing.



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     5.27 BANK MERGERS. At the written request of the Buyer, the Seller shall
take and shall cause its bank subsidiaries to take all necessary actions to
effectuate mergers of each of its subsidiary banks with a subsidiary bank of the
Buyer as soon as practicable after the Effective Time and in accordance with the
requirements of all applicable laws and regulations.

                                   ARTICLE VI

                               CLOSING CONDITIONS
                               ------------------

     6.01 CONDITIONS TO EACH PARTY'S OBLIGATIONS UNDER THIS AGREEMENT. The
respective obligations of each party under this Agreement shall be subject to
the fulfillment at or prior to the Effective Time of the following conditions,
none of which may be waived:

          (a) STOCKHOLDERS' APPROVAL. This Agreement and the Plan of Merger and
     the transactions contemplated hereby and thereby shall have been approved
     by the affirmative vote of the holders of at least two-thirds of the
     outstanding shares of Seller Common Stock and at least a majority of those
     shares of Buyer Common Stock present and voting at a meeting of such
     stockholders, in each case in accordance with applicable law.

          (b) GOVERNMENTAL CONSENTS. All authorizations, consents, orders or
     approvals of, or declarations or filings with, and all expirations of
     waiting periods imposed by, any governmental or regulatory authority or
     agency (all of the foregoing being referred to as "CONSENTS") which are
     necessary for the consummation of the Merger, other than Consents the
     failure of which to obtain would neither make it impossible to consummate
     the Merger nor result in a Material Adverse Effect on the Buyer (on a
     consolidated basis with the Seller) after the Merger, shall have been
     filed, occurred or been obtained (all such authorizations, orders,
     declarations, approvals, filings and consents and the lapse of all such
     waiting periods being referred to as the "REQUISITE REGULATORY APPROVALS")
     and all such Requisite Regulatory Approvals shall be in full force and
     effect. In addition, the Buyer shall have received all state securities or
     blue sky permits and other authorizations necessary to issue Buyer Common
     Stock pursuant to the Merger in accordance with all applicable state
     securities or blue sky laws.

          (c) S-4. The S-4 shall have become effective under the Securities Act
     and shall not be subject to a stop order or a threatened stop order.

          (d) NO INJUNCTIONS OR RESTRAINTS. No temporary restraining order,
     preliminary or permanent injunction or other order issued by any court of
     competent jurisdiction or other legal restraint or prohibition (an
     "INJUNCTION") preventing the consummation of the Merger shall be in effect.

          (e) ACCOUNTING TREATMENT. Each of the parties shall have received a
     letter from Arthur Andersen, LLP, dated the date of the Closing,
     substantially to the effect that on the basis of a review of this Agreement
     and the transactions contemplated hereby, in such accountants' opinion,
     Accounting Principles Board Opinion No. 16 provides that the Merger may be
     accounted for as a pooling of interests.

     6.02 CONDITIONS TO THE OBLIGATIONS OF THE BUYER UNDER THIS AGREEMENT. The
obligations of the Buyer under this Agreement shall be further subject to the
satisfaction or waiver by the Buyer, at or prior to the Effective Time, of the
following conditions:

          (a) ABSENCE OF MATERIAL ADVERSE CHANGES. There shall not have occurred
     any change in the business, assets, financial condition, or results of
     operations of the Seller or any of its subsidiaries which has had, or is
     reasonably likely to have, individually or in the 


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     aggregate, a Material Adverse Effect on the Seller taken as a whole, or any
     of the Seller's banking subsidiaries taken on an individual basis.

          (b) REPRESENTATIONS AND WARRANTIES; PERFORMANCE OF OBLIGATIONS. (i)
     The obligations of the Seller required to be performed by it at or prior to
     the Closing pursuant to the terms of this Agreement shall have been duly
     performed and complied with in all material respects and (ii) the
     representations and warranties of the Seller contained in this Agreement
     shall be true and correct in all material respects as of the date of this
     Agreement and as of the Effective Time as though made at and as of the
     Effective Time (except as otherwise specifically contemplated by this
     Agreement and except as to any representation or warranty which
     specifically relates to an earlier date); PROVIDED, HOWEVER, that for
     purposes of determining the satisfaction of the conditions contained in
     clause (ii) of this paragraph (b), no effect shall be given to any
     exception in such representations and warranties relating to materiality or
     the existence of a Material Adverse Effect and, PROVIDED FURTHER, HOWEVER,
     that for purposes of clause (ii) of this paragraph (b), such
     representations and warranties shall be deemed to be true and correct in
     all material respects unless the failure or failures of such
     representations and warranties to be so true and correct, in the aggregate,
     represents a material adverse change from the business, assets, financial
     condition or results of operations of the Seller taken as a whole, or any
     of the Seller's banking subsidiaries taken on an individual basis, as
     represented herein. The Buyer shall have received a certificate to the
     foregoing effect signed by the chairman or president and the chief
     financial officer or chief accounting officer of the Seller.

          (c) THIRD-PARTY APPROVALS. Any and all permits, consents, waivers,
     clearances, approvals and authorizations of all non-governmental and
     non-regulatory third parties which are necessary in connection with the
     consummation of the transactions contemplated by this Agreement and are
     required to be received or obtained by the Seller, shall have been obtained
     by the Seller, other than permits, consents, waivers, clearances, approvals
     and authorizations the failure of which to obtain would neither make it
     impossible to consummate the Merger nor result in any Material Adverse
     Effect with respect to the Buyer (on a consolidated basis with the Seller).

          (d) TAX OPINION. The Buyer shall have received an opinion, dated the
     date of the Closing from its counsel, Bingham, Dana & Gould LLP or other
     counsel acceptable to the Buyer and the Seller, substantially to the effect
     that, on the basis of facts and representations set forth therein, or set
     forth in writing elsewhere and referred to therein, for federal income tax
     purposes the Merger constitutes a reorganization as described in Section
     368(a) of the Code and addressing such other substantial federal income tax
     effects of the Merger as the Buyer may reasonably require and which are
     customary in transactions of a like character. In rendering any such
     opinion, such counsel may rely, to the extent they deem necessary or
     appropriate, upon opinions of other counsel and upon representations of an
     officer or officers of the Seller and the Buyer or any of their affiliates.

          (e) SELLER AFFILIATES AGREEMENTS. The Seller shall have delivered to
     the Buyer the letter pertaining to the Seller Affiliates, as contemplated
     under Section 5.06 above, and each of the executed Seller Affiliates
     Agreements that have been received by the Seller as of the Effective Time.

          (f) TERMINATION OF CERTAIN BENEFIT PLANS. The Seller shall have
     terminated the Seller's 1993 Employee Stock Purchase Plan and the Seller's
     Deferred Compensation Plan.

          (g) BURDENSOME CONDITION. There shall not be any action taken by any
     federal or state governmental agency or authority which, in connection with
     the granting of any Consent or Requisite Regulatory Approval necessary to
     consummate the Merger or 


                                      A-36
<PAGE>   137

     otherwise, imposes any condition or restriction upon the Buyer, any
     subsidiary of the Buyer or the Seller after the Merger (including, without
     limitation, requirements relating to the disposition of assets or
     limitations on interest rates), which would so materially adversely impact
     the economic or business benefits of the transactions contemplated by this
     Agreement as to render inadvisable in the reasonable judgment of the Buyer
     the consummation of the Merger.

     6.03 CONDITIONS TO THE OBLIGATIONS OF THE SELLER UNDER THIS AGREEMENT. The
obligations of the Seller under this Agreement shall be further subject to the
satisfaction or waiver by the Seller, at or prior to the Effective Time, of the
following conditions:

          (a) ABSENCE OF MATERIAL ADVERSE CHANGES. There shall not have occurred
     any change in the business, assets, financial condition or results of
     operations of the Buyer or any of its subsidiaries which has had, or is
     reasonably likely to have, individually or in the aggregate, a Material
     Adverse Effect on the Buyer taken as a whole with its subsidiaries, or on
     any of the Buyer's banking subsidiaries on an individual basis.

          (b) REPRESENTATIONS AND WARRANTIES; PERFORMANCE OF OBLIGATIONS. (i)
     The obligations of the Buyer required to be performed by it at or prior to
     the Closing pursuant to the terms of this Agreement shall have been duly
     performed and complied with in all material respects and (ii) the
     representations and warranties of the Buyer contained in this Agreement
     shall be true and correct in all material respects as of the date of this
     Agreement and as of the Effective Time as though made at and as of the
     Effective Time (except as otherwise specifically contemplated by this
     Agreement and except as to any representation or warranty which
     specifically relates to an earlier date); PROVIDED, HOWEVER, that for
     purposes of determining the satisfaction of the conditions contained in
     clause (ii) of this paragraph (b), no effect shall be given to any
     exception in such representations and warranties relating to materiality or
     the existence of a Material Adverse Effect and, PROVIDED FURTHER, HOWEVER,
     that for purposes of clause (ii) of this paragraph (b), such
     representations and warranties shall be deemed to be true and correct in
     all material respects unless the failure or failures of such
     representations and warranties to be so true and correct, in the aggregate,
     represents a material adverse change from the business, assets, financial
     condition or results of operations of the Buyer taken as a whole, or any of
     the Buyer's banking subsidiaries taken on an individual basis, as
     represented herein. The Seller shall have received a certificate to the
     foregoing effect signed by the chairman or president and the chief
     financial officer or chief accounting officer of the Buyer.

          (c) THIRD-PARTY APPROVALS. Any and all permits, consents, waivers,
     clearances, approvals and authorizations of all non-governmental and
     non-regulatory third parties which are necessary in connection with the
     consummation of the transactions contemplated by this Agreement and are
     required to be received or obtained by the Buyer, shall have been obtained
     by the Buyer, other than permits, consents, waivers, clearances, approvals
     and authorizations the failure of which to obtain would neither make it
     impossible to consummate the Merger nor result in a Material Adverse Effect
     on the Buyer (on a consolidated basis with the Seller) after the Merger.

          (d) TAX OPINION. The Seller shall have received an opinion, dated the
     dates of the Proxy Statement and the Closing from its tax advisor Arthur
     Andersen LLP or other tax advisor acceptable to the Buyer and the Seller,
     substantially to the effect that, on the basis of facts and representations
     set forth therein, or set forth in writing elsewhere and referred to
     therein, for federal income tax purposes the Merger constitutes a
     reorganization as described in Section 368(a) of the Code and that no gain
     or loss will be recognized by the stockholders of the Seller upon the
     receipt, pursuant to this Agreement, of Buyer Common Stock solely in
     exchange for Seller Common Stock (it being understood that such opinion
     will not extend to 

                                      A-37
<PAGE>   138

     cash received in lieu of fractional share interests or cash received by
     dissenters, if any) and in respect of such other substantial federal income
     tax effects of the Merger as the Seller may reasonably require and which
     are customary in transactions of a like character. In rendering any such
     opinion, such advisor may rely, to the extent they deem necessary or
     appropriate, upon opinions of other advisors and upon representations of an
     officer or officers of the Seller and the Buyer or any of their affiliates.

          (e) BUYER AFFILIATES AGREEMENTS. The Buyer shall have delivered to the
     Seller the letter pertaining to the Buyer Affiliates, as contemplated under
     Section 5.06 above, and each of the executed Buyer Affiliates Agreements
     that have been received by the Buyer as of the Effective Time.

          (f) NASDAQ LISTING. The shares of Buyer Common Stock issuable to
     Seller's stockholders pursuant to this Agreement and the Plan of Merger
     shall have been authorized for listing on the NASDAQ upon official notice
     of issuance.

          (g) EXCHANGE AGENT CERTIFICATION. The Exchange Agent (as defined in
     the Plan of Merger) shall have delivered to the Seller a certificate, dated
     as of the Effective Time, to the effect that the Exchange Agent has
     received from the Buyer appropriate instructions and authorization for the
     Exchange Agent to issue a sufficient number of shares of Buyer Common Stock
     in exchange for all outstanding shares of Seller Common Stock and has
     deposited with the Exchange Agent sufficient funds to pay a reasonable
     estimate of the cash payments necessary to pay for fractional share
     interests.

                                   ARTICLE VII

                                     CLOSING
                                     -------

     7.01 TIME AND PLACE. Subject to the provisions of Articles VI and VIII
hereof, the Closing of the transactions contemplated hereby shall take place at
the Boston, Massachusetts offices of Bingham, Dana & Gould LLP at 10:00 A.M.,
local time, on the first business day after the date on which all of the
conditions contained in Article VI are satisfied or waived; or at such other
place, at such other time, or on such other date as the Seller and the Buyer may
mutually agree upon for the Closing to take place; PROVIDED, that the Closing
shall in no event take place prior to January 10, 1997.

     7.02 DELIVERIES AT THE CLOSING. Subject to the provisions of Articles VI
and VIII hereof, at the Closing there shall be delivered to the Seller and the
Buyer, the opinions, certificates, and other documents and instruments required
to be delivered under Article VI hereof.

                                  ARTICLE VIII

                        TERMINATION, AMENDMENT AND WAIVER
                        ---------------------------------

     8.01 TERMINATION. This Agreement may be terminated at any time prior to the
Effective Time, whether before or after approval of this Agreement and the Plan
of Merger and the transactions contemplated hereby and thereby by the Seller's
stockholders:

          (a) by mutual written consent of the Seller and the Buyer authorized
     by their respective Boards of Directors;

          (b) by the Seller or the Buyer if the Effective Time shall not have
     occurred on or prior to June 30, 1997 (the "TERMINATION DATE") or such
     later date as shall have been agreed to in writing by the Buyer and the
     Seller;


                                      A-38
    



<PAGE>   139

          (c) by the Buyer or the Seller if any governmental or regulatory
     authority or agency, or court of competent jurisdiction, shall have issued
     a final permanent order or Injunction enjoining, denying approval of, or
     otherwise prohibiting the consummation of the Merger and the time for
     appeal or petition for reconsideration of such order or Injunction shall
     have expired without such appeal or petition being granted; or

          (d) by the Buyer or the Seller (provided that the terminating party is
     not then in material breach of any representation, warranty or covenant or
     other agreement contained herein or in the Seller Option Agreement) if the
     approval of such Person's stockholders specified in Section 5.05 shall not
     have been obtained by reason of the failure to obtain the required vote at
     a duly held meeting of such stockholders or at any adjournment thereof; or

          (e) by the Board of Directors of the Buyer or the Board of Directors
     of the Seller (provided that the terminating party is not then in material
     breach of any representation, warranty, covenant or other agreement
     contained herein pursuant to the standard set forth in Section 6.02(b) or
     6.03(b), as may be applicable or in the Seller Option Agreement), in the
     event of a material breach by the other party of any representation,
     warranty, covenant or other agreement contained herein pursuant to the
     standard set forth in Section 6.02(b) or 6.03(b), as may be applicable or
     in the Seller Option Agreement which breach is not cured after forty-five
     (45) days written notice thereof is given to the party committing such
     breach; or

          (f) by the Seller, by action of its Board of Directors, whether before
     or after approval of the Merger by the stockholders of the Seller, by
     giving written notice of such election to the Buyer in the event that both
     of the following conditions are satisfied:

               (i) the average per share last sale prices of Buyer Common Stock
          as reported on NASDAQ over the ten (10) consecutive trading day period
          immediately preceding the date of the last Requisite Regulatory
          Approval to be received, in this case without regard to any waiting
          period attached to the effectiveness thereof (such period being
          hereinafter referred to as the "DETERMINATION PERIOD", and the price
          so obtained being referred to as, THE "CLOSING PRICE") is less than
          $13.81; and

               (ii) the number obtained by dividing the Closing Price by 16.25
          is less than the number obtained by subtracting (A) 0.15 from (B) the
          quotient obtained by dividing the Final Index Price (as defined below)
          by the Initial Index Price (as defined below).

          For the purposes hereof the following terms shall have the following
     meanings:

          "FINAL INDEX PRICE" shall mean the Weighted Average of the average of
     the closing prices of the Index Companies as reported on the NYSE, NASDAQ
     or AMEX for the Determination Period.

          "INDEX COMPANIES" shall mean the companies listed on EXHIBIT E hereto.

          "INITIAL INDEX PRICE" shall mean the Weighted Average of the closing
     prices of the Index Companies as reported on the NYSE, NASDAQ or AMEX on
     the trading day immediately preceding execution of this Agreement.

          "WEIGHTED AVERAGE" shall mean the average determined by giving the
     average of the closing prices for each of the Index Companies the
     corresponding weight listed on EXHIBIT E hereto.


                                      A-39
<PAGE>   140

     If the Buyer or any company listed on EXHIBIT E declares a stock dividend
     or effects a reclassification, recapitalization, split-up, combination, or
     subdivision of its common stock between the trading day immediately
     preceding execution of this Agreement and the date of the last Requisite
     Regulatory Approval to be received (without regard to any waiting period
     attached to the effectiveness thereof), the closing prices for such common
     stock shall be appropriately adjusted for the purposes of the definitions
     above so as to be comparable to the price on the date immediately preceding
     execution of this Agreement. There shall be excluded from the list of
     companies on EXHIBIT E any company as to which there is pending at any time
     during the Determination Period any publicly announced proposal for such
     company to be acquired by another company in exchange for its stock.

     Notwithstanding the foregoing, during the ten (10) business day period
     commencing with the Buyer's receipt of the Seller's notice of termination
     pursuant to this Section 8.01(f), the Buyer shall have the option to
     increase the consideration to be received by the holders of Seller Common
     Stock under the Plan of Merger by adjusting the Conversion Number
     (hereinafter, as such term is defined in the Plan of Merger) to equal a
     number (calculated to the nearest one-thousandth) obtained by dividing (x)
     $26.24 by (y) the Closing Price. If the Buyer so elects within such ten-day
     period, it shall give prompt written notice to the Seller of such election
     and the revised Conversion Number, whereupon no termination shall have
     occurred pursuant to this Section 8.01(f) and the Agreement shall remain in
     effect in accordance with its terms (except as the Conversion Number shall
     have been so modified).

          (g) By the Board of Directors of either party (provided that the
     terminating party is not then in breach of any representation or warranty,
     covenant or other agreement contained in this Agreement or in the Seller
     Option Agreement) in the event that any of the conditions precedent to the
     obligations of such party to consummate the Merger cannot be satisfied or
     fulfilled by the date specified in Section 8.01(b) of this Agreement.

     8.02 EFFECT OF TERMINATION. In the event of termination of this Agreement
by either the Seller or the Buyer as provided above, this Agreement shall
forthwith become null and void (other than Sections 5.02(b) and 9.01 hereof,
which shall remain in full force and effect) and there shall be no further
liability on the part of the Seller or the Buyer or their respective officers or
directors to the other, except (i) any liability of the Seller and the Buyer
under said Sections 5.02(b) and 9.01, (ii) that the Seller Option Agreement
shall be governed by its own terms as to termination, (iii) the Confidentiality
Agreement shall survive in accordance with its terms and (iv) in the event of a
willful breach of any representation, warranty, covenant or agreement contained
in this Agreement, in which case, the breaching party shall remain liable for
any and all damages, costs and expenses, including all reasonable attorneys'
fees, sustained or incurred by the non-breaching party as a result thereof or in
connection therewith or with the enforcement of its rights hereunder.

     8.03 AMENDMENT, EXTENSION AND WAIVER. Subject to applicable law and as may
be authorized by their respective Boards of Directors, at any time prior to the
consummation of the transactions contemplated by this Agreement or termination
of this Agreement in accordance with the provisions of Section 8.01 hereof,
whether before or after approval thereof by the stockholders of the Seller, the
Buyer and the Seller may, (a) amend this Agreement, (b) extend the time for the
performance of any of the obligations or other acts of any other party hereto,
(c) waive any inaccuracies in the representations and warranties contained
herein or in any document delivered pursuant hereto, or (d) waive compliance
with any of the agreements or conditions contained in Articles V and VI (other
than Section 6.01) hereof; PROVIDED, HOWEVER, that after any approval of the
transactions contemplated by this Agreement by the Seller's or the Buyer's
stockholders, there may not be, without further approval of such stockholders,
any amendment, extension or waiver of this Agreement which reduces the amount or
changes the form of the consideration to be delivered to the stockholders of the
Seller hereunder other than as contemplated by this Agreement. This Agreement
may not be amended except by an instrument in writing signed on behalf of each
of the 

                                      A-40
<PAGE>   141
parties hereto. Any agreement on the part of a party hereto to any extension or
waiver shall be valid only if set forth in an instrument in writing signed on
behalf of such party, but such waiver or failure to insist on strict compliance
with such obligation, covenant, agreement or condition shall not operate as a
waiver of, or estoppel with respect to, any subsequent or other failure.

                                   ARTICLE IX

                                  MISCELLANEOUS
                                  -------------

     9.01 EXPENSES. Except as may otherwise be agreed to hereunder or in other
writing by the parties, all legal and other costs and expenses incurred in
connection with this Agreement and the transactions contemplated hereby shall be
paid by the party incurring such costs and expenses; PROVIDED, HOWEVER, that all
such costs and expenses incurred in connection with the printing and mailing of
the S-4 and the Proxy Statement shall be borne equally by the Buyer and the
Seller.

     9.02 SURVIVAL. None of the representations, warranties, covenants and
agreements of the Seller or the Buyer shall survive after the Effective Time,
except for the agreements and covenants contained or referred to in Article II,
Section 5.02(b), the last sentence of Section 5.07, and Sections 5.09, 5.11,
5.13 and 5.15 hereof, and the agreements of the "affiliates" of the Seller
delivered pursuant to Section 5.06, which agreements and covenants shall survive
the Effective Time.

     9.03 NOTICES. All notices or other communications hereunder shall be in
writing and shall be deemed given if delivered personally or mailed by prepaid
registered or certified mail (return receipt requested) or by telecopy, cable,
telegram or telex addressed as follows:

               (a)     If to the Seller, to:
                       Walden Bancorp, Inc.
                       125 Nagog Park
                       Acton, Massachusetts 01720
                       Attention: Mr. David E. Bradbury
                                  Chairman of the Board,
                                   President and Chief Executive
                                   Officer
                       Facsimile No.: (508) 635-5052

        with a required copy to:
                Housely, Kantarian & Bronstein, P.C.
                1220 19th Street, N.W.
                Suite 700
                Washington, D.C. 20036
                Attention:  Harry K. Kantarian, Esq.
                Facsimile No.:  (202) 822-0140

               (b)     If to the Buyer, to:
                       UST Corp.
                       40 Court Street
                       Boston, Massachusetts 02108
                       Attention:  Mr. Neal F. Finnegan
                                   President and
                                    Chief Executive Officer
                       Facsimile No.:  (617) 726-7320

                                      A-41
<PAGE>   142


        with required copies to:
                UST Corp.
                40 Court Street
                Boston, Massachusetts 02108
                Attention:  Eric R. Fischer, Esq.
                Facsimile No.:  (617) 726-7320

        and

                Bingham, Dana & Gould LLP
                150 Federal Street
                Boston, Massachusetts 02110
                Attention:     Neal J. Curtin, Esq.
                                       and
                               Maria M. Park, Esq.
                Facsimile No.:  (617) 951-8736

or such other address as shall be furnished in writing by any party, and any
such notice or communication shall be deemed to have been given as of the date
so mailed.

     9.04 PARTIES IN INTEREST. This Agreement shall be binding upon and shall
inure to the benefit of the parties hereto and their respective successors and
assigns; PROVIDED, HOWEVER, that neither this Agreement nor any of the rights,
interests or obligations hereunder shall be assigned by any party hereto without
the prior written consent of the other parties, and that nothing in this
Agreement is intended to confer, expressly or by implication, upon any other
person any rights or remedies under or by reason of this Agreement except as
reflected in Sections 5.09, 5.13(d) and 5.15.

     9.05 COMPLETE AGREEMENT. This Agreement, including the documents and other
writings referred to herein or delivered pursuant hereto, including the
Confidentiality Agreement, the Plan of Merger and the other Transaction
Documents, contains the entire agreement and understanding of the parties with
respect to its subject matter. Except as set forth in the Transaction Documents
or in the Disclosure Schedules, there are no restrictions, agreements, promises,
warranties, covenants or undertakings between the parties other than those
expressly set forth herein or therein. This Agreement supersedes all prior
agreements (other than the Confidentiality Agreement) and understandings between
the parties, both written and oral, with respect to its subject matter.

     9.06 COUNTERPARTS. This Agreement may be executed in counterparts, all of
which shall be considered one and the same agreement and each of which shall be
deemed to be an original and shall become effective when a counterpart has been
signed by each of the parties and delivered to each of the other parties.

     9.07 GOVERNING LAW. This Agreement shall be governed by the laws of The
Commonwealth of Massachusetts, without giving effect to the principles of
conflicts of laws thereof.

     9.08 CAPTIONS. The Article and Section headings contained in this Agreement
are for reference purposes only and shall not affect in any way the meaning or
interpretation of this Agreement.

     9.09 EFFECT OF INVESTIGATIONS. No investigation by the parties hereto made
heretofore or hereafter, whether pursuant to this Agreement or otherwise shall
affect the representations and warranties of the parties which are contained
herein and each such representation and warranty shall survive such
investigation, subject, however, to Section 9.02 hereof.

                                      A-42

<PAGE>   143

     9.10 SEVERABILITY. In the event that any one or more provisions of this
Agreement shall for any reason be held invalid, illegal or unenforceable in any
respect, by any court of competent jurisdiction, such invalidity, illegality or
unenforceability shall not affect any other provisions of this Agreement and the
parties shall use their best efforts to substitute a valid, legal and
enforceable provision which, insofar as practicable, implements the purposes and
intents of this Agreement.

     9.11 SPECIFIC ENFORCEABILITY. The parties recognize and hereby acknowledge
that it is impossible to measure in money the damages that would result to a
party by reason of the failure of either of the parties to perform any of the
obligations imposed on it by this Agreement. Accordingly, if any party should
institute an action or proceeding seeking specific enforcement of the provisions
hereof, each party against which such action or proceeding is brought hereby
waives the claim or defense that the party instituting such action or proceeding
has an adequate remedy at law and hereby agrees not to assert in any such action
or proceeding the claim or defense that such a remedy at law exists.

     IN WITNESS WHEREOF, the Seller and the Buyer have caused this Agreement to
be executed as a sealed instrument by their duly authorized officers as of the
day and year first above written.

                                      UST CORP.

                                      By:    /s/  Neal F. Finnegan
                                             --------------------------
                                             Name:     Neal F. Finnegan
                                             Title:    President

                                      WALDEN BANCORP, INC.

                                      By:    /s/  David E. Bradbury
                                             ---------------------------
                                             Name:     David E. Bradbury
                                             Title:    President

                                      A-43

<PAGE>   144
                                                                     EXHIBIT B-1
                                                                     -----------
                FORM OF BUYER AFFILIATE LETTER ADDRESSED TO SELLER

                                                              [Date]

Walden Bancorp, Inc.
125 Nagog Park
P.O. Box 2100
Acton, Massachusetts  01720-6100

Ladies and Gentlemen:

     I have been advised that as of the date hereof I may be deemed to be an
"affiliate" of UST CORP., a Massachusetts corporation ("Buyer"), as the term
"affiliate" is used in and for purposes of Accounting Series Releases 130 and
135, as amended, of the Securities and Exchange Commission (the "Commission"). I
have been further advised that pursuant to the terms of the Affiliation
Agreement and Plan of Reorganization and Agreement and Plan of Merger dated as
of August 30, 1996 (together, the "Merger Agreement"), between Buyer, MOSAIC
CORP., a wholly owned subsidiary of Buyer and a Massachusetts corporation
("Merger Subsidiary"), and WALDEN BANCORP, INC., a Massachusetts CORPORATION
(the "Seller"), Merger Subsidiary will be merged with and into Seller.

     I represent to and covenant with Buyer that from the date that is thirty
(30) days prior to the Effective Time (as defined in the Merger Agreement) I
will not sell, transfer or otherwise dispose of, or reduce the risk of ownership
with respect to, shares of Buyer Common Stock (as defined in the Merger
Agreement) held by me until after such time as results covering at least thirty
(30) days of combined operations of Buyer and Seller have been published by
Buyer, in the form of a quarterly earnings report, an effective registration
statement filed with the Commission, a report to the Commission on Form 10-K,
10-Q, or 8-K, or any other public filing or announcement which includes the
results of at least 30 days of combined operations.

                                     Very truly yours,

                                     By:________________________________
                                        Name:

Accepted this ____ day of
_____________, 1996, by

WALDEN BANCORP, INC.

By:__________________________________
        Name:
        Title:


                                     A-44
<PAGE>   145



                                                                     EXHIBIT B-2
                                                                     -----------



               FORM OF SELLER AFFILIATE LETTER ADDRESSED TO BUYER

                                                     [Date]

UST Corp.
40 Court Street
Boston, Massachusetts  02108

Ladies and Gentlemen:

     I have been advised that as of the date hereof I may be deemed to be an
"affiliate" of WALDEN BANCORP, INC., a Massachusetts corporation ("Seller"), as
the term "affiliate" is (i) defined for purposes of paragraphs (c) and (d) of
Rule 145 of the Rules and Regulations (the "Rules and Regulations") of the
Securities and Exchange Commission (the "Commission") under the Securities Act
of 1933, as amended (the "Act"), and/or (ii) used in and for purposes of
Accounting Series Releases 130 and 135, as amended, of the Commission. I have
been further advised that pursuant to the terms of the Affiliation Agreement and
Plan of Reorganization and Agreement and Plan of Merger dated as of August 30,
1996 (together, the "Merger Agreement"), between UST CORP., a Massachusetts
corporation ("Buyer"), MOSAIC CORP., a wholly owned subsidiary of Buyer and a
Massachusetts corporation ("Merger Subsidiary"), and Seller, Merger Subsidiary
will be merged with and into Seller (the "Merger"), and that as a result of the
Merger, I may receive shares of Buyer Common Stock (as defined in the Merger
Agreement) in exchange for shares of Seller Common Stock (as defined in the
Merger Agreement), owned by me.

     I represent, warrant and covenant to Buyer that in the event I receive any
Buyer Common Stock pursuant to the Merger:

          A. I shall not make any sale, transfer or other disposition of the
     Buyer Common Stock in violation of the Act or the Rules and Regulations.

          B. I have carefully read this letter and the Agreement and discussed
     its requirements and other applicable limitations upon my ability to sell,
     transfer or otherwise dispose of Buyer Common Stock to the extent I
     believed necessary, with my counsel or counsel for Seller.

          C. I have been advised that the issuance of Buyer Common Stock to me
     pursuant to the Merger has been or will be registered with the Commission
     under the Act on a Registration Statement on Form S-4. However, I have also
     been advised that, because, at the time the Merger is or was submitted for
     a vote of the stockholders of Buyer, I may be deemed to be or to have been
     an affiliate of Seller and the distribution by me of the Buyer Common Stock
     will not have been registered under the Act. I agree that I will not sell,
     transfer or otherwise dispose of Buyer Common Stock issued to me in the
     Merger unless (i) such sale, transfer or other disposition has been
     registered under the Act, (ii) such sale, transfer or other disposition is
     made in conformity with the volume and other limitations of Rule 145
     promulgated by the Commission under the Act, or (iii) in the opinion of
     counsel reasonably acceptable to Buyer, such sale, transfer or other
     disposition is otherwise exempt from registration under the Act.

          D. I understand that Buyer is under no obligation to register the
     sale, transfer or other disposition of the Buyer Common Stock by me or on
     my behalf under the Act or to take any other action necessary in order to
     make compliance with an exemption from such registration available.


                                      A-45

<PAGE>   146




          E. I also understand that stop transfer instructions will be given to
     Buyer's transfer agents with respect to the Buyer Common Stock and that
     there will be placed on the certificates for the Buyer Common Stock issued
     to me, or any substitutions therefor, a legend stating in substance:

               "The securities represented by this certificate have been issued
          in a transaction to which Rule 145 promulgated under the Securities
          Act of 1933 applies and may be sold or otherwise transferred only in
          compliance with the requirements of Rule 145 or pursuant to a
          registration statement under said act or an exemption from such
          registration."

          F. I also understand that unless the transfer by me of my Buyer Common
     Stock has been registered under the Act or is a sale made in conformity
     with the provisions of Rule 145, Buyer reserves the right to put the
     following legend on the certificates issued to my transferee:

               "The shares represented by this certificate have not been
          registered under the Securities Act of 1933 and were acquired from a
          person who received such shares in a transaction to which Rule 145
          promulgated under the Securities Act of 1933 applies. The shares have
          been acquired by the holder not with a view to, or for resale in
          connection with, any distribution thereof within the meaning of
          Securities Act of 1933 and may not be sold, pledged or otherwise
          transferred except in accordance with an exemption from the
          registration requirements of the Securities Act of 1933."

     It is understood and agreed that this letter agreement shall terminate and
be of no further force and effect and the legends set forth in E or F, as the
case may be, above shall be removed by delivery of substitute certificates
without such legend, and the related stop transfer of restrictions shall be
lifted forthwith, if (i) any such shares of Buyer Common Stock shall have been
registered under the Securities Act for sale, transfer or other disposition by
me or on my behalf and are sold, transferred or otherwise disposed of, or (ii)
any such shares of Buyer Common Stock are sold in accordance with the provisions
of paragraphs (c), (e), (f) and (g) of Rule 144 promulgated under the Securities
Act, or (iii) I am not at the time an affiliate of Buyer and have been the
beneficial owner of the Buyer Common Stock for at least two years (or such other
period as may be prescribed by the Securities Act and the rules and regulations
promulgated thereunder), and Buyer has filed with the Commission all of the
reports it is required to file under the Securities Exchange Act of 1934, as
amended, during the preceding twelve months, or (iv) I am not and have not been
for at least three months an affiliate of Buyer and have been the beneficial
owner of the Buyer Common Stock for at least three years (or such period as may
be prescribed by the Securities Act and the rules and regulations promulgated
thereunder), or (v) Buyer shall have received a letter from the staff of the
Commission, or an opinion of counsel reasonably acceptable to Buyer, to the
effect that the stock transfer restrictions and the legend are not required.

     I further represent to and covenant with Buyer that from the date that is
thirty (30) days prior to the Effective Time (as defined in the Merger
Agreement) I will not sell, transfer or otherwise dispose of, or reduce the risk
of ownership with respect to, shares of Seller Common Stock held by me and that
I will not sell, transfer or otherwise dispose of, or reduce the risk of
ownership with respect to, any shares of Buyer Common Stock received by me in
the Merger or other shares of Buyer Common Stock until after such time as
results covering at least thirty (30) days of combined


                                      A-46

<PAGE>   147



operations of Buyer and Seller have been published by Buyer, in the form of a
quarterly earnings report, an effective registration statement filed with the
Commission, a report to the Commission on Form 10-K, 10-Q, or 8-K, or any other
public filing or announcement which includes the results of at least 30 days of
combined operations.

                                Very truly yours,

                                By:_______________________________
                                   Name:

Accepted this ____ day of
_____________, 1996, by

UST CORP.

By:_________________________________
    Name:
    Title:



                                      A-47

<PAGE>   148

                                                                       EXHIBIT D
                                                                       ---------

                                 August 30, 1996

Neal F. Finnegan, President
   and Chief Executive Officer
UST Corp.
40 Court Street
Boston, Massachusetts  02108

Dear Neal:

     The undersigned (the "STOCKHOLDER") owns and has sole voting power with
respect to the number of shares of the common stock, par value $1.00 per share
(the "SHARES"), of Walden Bancorp, Inc., a Massachusetts corporation (the
"SELLER"), indicated opposite the Stockholder's name on SCHEDULE 1 attached
hereto.

     Simultaneously with the execution of this letter agreement, UST Corp. (the
"BUYER") and the Seller are entering into an Affiliation Agreement and Plan of
Reorganization (as amended and in effect from time to time, the "ACQUISITION
AGREEMENT") providing, among other things, for the indirect acquisition of the
Seller by the Buyer (the "ACQUISITION").

     In consideration of, and as a condition to, the Buyer's entering into the
Acquisition Agreement the Stockholder and the Buyer agree as follows:

     1. The Stockholder, while this letter agreement is in effect, shall vote or
cause to be voted all of the Shares, as well as any other shares of common stock
of Seller of which the Stockholder acquires beneficial ownership and sole voting
power, whether pursuant to the exercise of stock options or otherwise, as long
as such shares are owned by the Stockholder as of the record date for the
special meeting of the Seller's stockholders to be called and held following the
date hereof, for the approval of the Acquisition Agreement and the Acquisition
and shall vote or cause to be voted all such shares, at such special meeting or
any other meeting of the Seller's stockholders following the date hereof,
against the approval of any other agreement providing for a merger, acquisition,
consolidation, sale of a material amount of assets or other business combination
of the Seller or any of its subsidiaries with any person or entity other than
the Buyer, or any subsidiary of the Buyer.

     2. The agreements contained herein are intended to relate to restrictions
on voting and to continue only for such time as may reasonably be necessary to
obtain all necessary approvals, including shareholder approval and all necessary
governmental approvals, of the Acquisition and all other transactions
contemplated by the Acquisition Agreement.

     3. Notwithstanding anything herein to the contrary, the agreements
contained herein shall remain in full force and effect until the earlier of (a)
the consummation of the Acquisition or (b) the termination of the Acquisition
Agreement in accordance with Article VIII thereof.

     4. The Stockholder has signed this letter agreement intending to be bound
thereby. The Stockholder expressly agrees that this letter agreement shall be
specifically enforceable in any court of competent jurisdiction in accordance
with its terms against the Stockholder. All of the covenants and agreements
contained in this letter agreement shall be binding upon, and inure to the
benefit of, the respective parties and their permitted successors, assigns,
heirs, executors, administrators and other legal representatives, as the case
may be.

     5. This letter agreement may be executed in one or more counterparts, each
of which will be deemed an original but all of which together shall constitute
one and the same instrument.


                                      A-48
<PAGE>   149


     6. This letter agreement is deemed to be signed as a sealed instrument and
is to be governed by the laws of the Commonwealth of Massachusetts, without
giving effect to the principles of conflicts of laws thereof. If any provision
hereof is deemed unenforceable, the enforceability of the other provisions
hereof shall not be affected.

     If the foregoing accurately reflects your understanding of the subject
matter intended to be contained herein, please confirm our agreement by signing
this letter where indicated below.

                                Very truly yours,

                                /s/ David E. Bradbury
                                ---------------------------
                                David E. Bradbury






AGREED TO AND ACCEPTED AS OF
THE DATE FIRST ABOVE WRITTEN

UST CORP.

By: /s/ Neal F. Finnegan
   ---------------------------------------
   Name:    Neal F. Finnegan
   Title:   President and Chief Executive Officer

   

                                   Schedule 1
                                   ----------

                                      Number of Shares
Name of Stockholder             Owned with Sole Voting Power
- -------------------             ----------------------------

David E. Bradbury                          85,474




                                      A-49
<PAGE>   150


<TABLE>

                                    EXHIBIT E
                                    ---------
<CAPTION>

                                                                Weighting Index

<S>                                                                <C>    
Westamerica Bancorporation                                           5.88
Imperial Bancorp                                                     4.93
Riggs National Corporation                                           5.72
First Midwest Bancorp Inc.                                           4.75
Whitney Holding Corp.                                                6.61
Citizens Bancorp (Maryland)                                          5.62
Magna Group Inc.                                                     8.39
CCB Financial Corporation                                            9.90
Hubco Inc.                                                           3.45
Northfork Bancorporation                                             9.26
Trustco Bank Corp. NY                                                5.11
Cullen/Frost Bankers Inc.                                            7.93
Banknorth Group Inc.                                                 3.43
Associated Banc Corp.                                                8.72
People's Heritage Financial Group                                    6.85
Chittenden Corporation                                               3.45
                                                                   ------
                                                                   100.00%
</TABLE>


                                      A-50

<PAGE>   151


                                                                      APPENDIX B
                                                                      ----------

                          AGREEMENT AND PLAN OF MERGER

     AGREEMENT AND PLAN OF MERGER, dated as of August 30, 1996 (this "PLAN OF
MERGER") by and among UST CORP., a Massachusetts corporation (the "BUYER"),
WALDEN BANCORP, INC., a Massachusetts corporation (the "SELLER"), and MOSAIC
CORP., a Massachusetts corporation and a wholly-owned subsidiary of the Buyer
(the "MERGER SUBSIDIARY"). The Seller and the Merger Subsidiary are hereinafter
sometimes collectively referred to as the "CONSTITUENT CORPORATIONS".

     This Plan of Merger is being entered into pursuant to an Affiliation
Agreement and Plan of Reorganization, dated as of August 30, 1996 (as amended
and in effect from time to time, the "AGREEMENT"), between the Buyer and the
Seller.

     All capitalized terms used herein without definition are used with the
meanings ascribed thereto in the Agreement.

     In consideration of the premises, and the mutual covenants and agreements
herein contained, the parties hereto agree as follows:

                                    ARTICLE I

                                   THE MERGER
                                   ----------

     1.01 SURVIVING CORPORATION. In accordance with the provisions of this Plan
of Merger and the Massachusetts Business Corporation Law ("MBCL"), at the
Effective Time (as hereinafter defined), the Merger Subsidiary shall be merged
with and into the Seller (the "MERGER"), and the separate corporate existence of
the Merger Subsidiary shall cease. The Seller shall be the surviving corporation
in the Merger (hereinafter sometimes referred to as the "SURVIVING CORPORATION")
and shall continue its corporate existence under the laws of the Commonwealth of
Massachusetts. The name of the Surviving Corporation shall be Mosaic Corp.,
unless such name is changed at the request of the Buyer.

     1.02 PURPOSES OF SURVIVING CORPORATION. As of the Effective Time, the
purposes of the Surviving Corporation shall be as stated in the Articles of
Organization of the Merger Subsidiary immediately prior to the Effective Time.

     1.03 AUTHORIZED CAPITAL STOCK OF SURVIVING CORPORATION. As of the Effective
Time, the Surviving Corporation shall be authorized to issue that number of
shares of $0.01 par value voting common stock which the Merger Subsidiary is
authorized to issue immediately prior to the Effective Time.

     1.04 DESCRIPTION OF CLASSES OF STOCK. As of the Effective Time, each class
or series of capital stock of the Surviving Corporation shall have the same
preferences, voting powers, qualifications, special or relative rights or
privileges as such class or series of capital stock of the Merger Subsidiary
possessed immediately prior to the Effective Time.

     1.05 Effect of the Merger.
          --------------------

               (a) Upon the Effective Time, all of the estate, property, rights,
          privileges, powers and franchises of the Constituent Corporations and
          all of their property, real, personal and mixed, and all the debts due
          on whatever account to any of them, as well as all stock subscriptions
          and other choses in action belonging to any of them, shall be
          transferred to and 



<PAGE>   152
          vested in the Surviving Corporation, without further act or deed, and
          all claims, demands, property and other interest shall be the property
          of the Surviving Corporation, and the title to all real estate vested
          in any of the Constituent Corporations shall not revert or be in any
          way impaired by reason of the Merger, but shall be vested in the
          Surviving Corporation.

               (b) Upon the Effective Time, the rights of creditors of any
          Constituent Corporation shall not in any manner be impaired, nor shall
          any liability or obligation, including taxes due or to become due, or
          any claim or demand in any cause existing against such corporation, or
          any stockholder, director, or officer thereof, be released or impaired
          by the Merger, but the Surviving Corporation shall be deemed to have
          assumed, and shall be liable for, all liabilities and obligations of
          each of the Constituent Corporations in the same manner and to the
          same extent as if the Surviving Corporation had itself incurred such
          liabilities or obligations. The stockholders, directors, and officers
          of the Constituent Corporations shall continue to be subject to all
          liabilities, claims and demands existing against them as such at or
          before the Merger. No action or proceeding then pending before any
          court or tribunal of the Commonwealth of Massachusetts or otherwise in
          which any Constituent Corporation is a party, or in which any such
          stockholder, director, or officer is a party, shall abate or be
          discontinued by reason of the Merger, but any such action or
          proceeding may be prosecuted to final judgment as though no merger had
          taken place, or the Surviving Corporation may be substituted as a
          party in place of any Constituent Corporation by the court in which
          such action or proceeding is pending.

     1.06 ADDITIONAL ACTIONS. If, at any time after the Effective Time, the
Surviving Corporation shall consider or be advised that any deeds, bills of
sale, assignments, assurances or any other actions or things are necessary or
desirable to vest, perfect or confirm of record or otherwise in the Surviving
Corporation its right, title or interest in, to or under any of the rights,
properties or assets of the Merger Subsidiary acquired or to be acquired by the
Surviving Corporation as a result of, or in connection with, the Merger or to
otherwise carry out this Plan of Merger, the officers and directors of the
Surviving Corporation shall and will be authorized to execute and deliver, in
the name and on behalf of the Constituent Corporations or otherwise, all such
deeds, bills of sale, assignments and assurances and to take and do, in the name
and on behalf of the Constituent Corporations or otherwise, all such other
actions and things as may be necessary or desirable to vest, perfect or confirm
any and all right, title and interest in, to and under such rights, properties
or assets in the Surviving Corporation or to otherwise carry out this Plan of
Merger.

     1.07 ARTICLES OF ORGANIZATION. At the Effective Time, the Articles of
Organization of the Merger Subsidiary as in effect at the Effective Time, shall
be by amendment effected by the Plan of Merger, the Articles of Organization of
the Surviving Corporation and the By-Laws of the Merger Subsidiary, as in effect
at the Effective Time, shall be the By-Laws of the Surviving Corporation and,
subject to the rights of the Buyer as the sole stockholder, shall thereafter
continue to be its Articles of Organization and By-Laws until amended as
provided therein or by law.

     1.08 DIRECTORS AND OFFICERS. At the Effective Time, the Board of Directors
of the Surviving Corporation shall consist of those persons comprising the Board
of Directors of the Merger Subsidiary prior to the Effective Time, each to hold
office in accordance with the Articles of Organization and By-Laws of the
Surviving Corporation. The officers of the Merger Subsidiary immediately prior
to the Effective Time shall be the officers of the Surviving Corporation from
and, subject to the rights of the Buyer as the sole stockholder, after the
Effective Time each to hold office in accordance with the Articles of
Organization and By-Laws of the Surviving Corporation.

     1.09 EFFECTIVE TIME; CONDITIONS. If all of the conditions precedent set
forth in Article VI of the Agreement have been satisfied or waived, and this
Plan of Merger is not terminated under Section 3.01 hereof, Articles of Merger
with respect to the Merger shall be prepared by the Merger Subsidiary and the
Seller and filed and recorded pursuant to Section 78(d) of the MBCL (the

                                      B-2

<PAGE>   153
"Articles of Merger"). The Merger shall become effective at, and the Effective
Time shall be, the date and time specified in the Articles of Merger which shall
be not later than thirty (30) days after the filing of the Articles of Merger
(such date and time is herein referred to as the "EFFECTIVE TIME").

                                   ARTICLE II

                              CONVERSION OF SHARES
                              --------------------

     2.01 Effect on Outstanding Shares.
          ----------------------------

               (a) MERGER SUBSIDIARY COMMON STOCK. By virtue of the Merger,
          automatically and without any action on the part of the holder
          thereof, each share of common stock of the Merger Subsidiary, par
          value $0.01 per share ("MERGER SUBSIDIARY COMMON STOCK"), issued and
          outstanding immediately prior to the Effective Time, shall become and
          be converted into 1.00 share of common stock of the Surviving
          Corporation, par value $0.01 per share ("SURVIVING CORPORATION COMMON
          STOCK"). Each certificate which immediately prior to the Effective
          Time represented outstanding shares of Merger Subsidiary Common Stock
          shall on and after the Effective Time be deemed for all purposes to
          represent the number of shares of Surviving Corporation Common Stock
          into which the shares of Merger Subsidiary Common Stock represented by
          such certificate shall have been converted pursuant to this Section
          2.01(a).

               (b) SELLER COMMON STOCK. (i) By virtue of the Merger,
          automatically and without any action on the part of the holder
          thereof, each share of common stock of the Seller, par value $1.00 per
          share ("SELLER COMMON STOCK"), issued and outstanding immediately
          prior to the Effective Time (other than any such shares held directly
          or indirectly by the Buyer, except in a fiduciary capacity, and any
          such shares held as treasury stock by the Seller) shall become and be
          converted into 1.9 shares of the common stock of the Buyer, par value
          $0.625 per share ("BUYER COMMON STOCK"), together with that number of
          Buyer rights issued pursuant to the Buyer Rights Agreement associated
          therewith; PROVIDED, HOWEVER, that in the event that the Buyer has
          exercised its option to deliver additional shares of its Common Stock
          pursuant to the last paragraph of Section 8.01(f) of the Agreement,
          Seller's Common Stock shall be converted into such number of shares of
          the Common Stock of the Buyer, par value $0.625 per share, as provided
          in said Section of the Agreement. The number of shares of Buyer Common
          Stock into which each share of Seller Common Stock shall be converted
          is hereinafter called the "CONVERSION NUMBER."

               (ii) As of the Effective Time, each share of Seller Common Stock
          held either directly or indirectly by the Buyer (other than in a
          fiduciary capacity) or as treasury stock of the Seller shall be
          cancelled, retired and cease to exist, and no payment shall be made
          with respect thereto. Each certificate which immediately prior to the
          Effective Time represented outstanding shares of Seller Common Stock
          shall on and after the Effective Time be deemed for all purposes to
          represent the number of shares of Buyer Common Stock into which the
          shares of Seller Common Stock represented by such certificate shall
          have been converted pursuant to this Section 2.01(b).

               (c) SHARES OF DISSENTING HOLDERS. No conversion under Section
          2.01(b) hereof shall be made with respect to the shares of Seller
          Common Stock held by a Dissenting Holder (as such term is defined
          below); PROVIDED, HOWEVER, that each share of Seller Common Stock
          outstanding immediately prior to the Effective Time and held by a
          Dissenting Holder who shall, after the Effective Time, withdraw his
          demand for appraisal or lose his right of appraisal, in either case
          pursuant to the applicable provisions of the MBCL, shall be deemed to
          be converted, as of the Effective Time, into shares of Buyer Common
          Stock as specified in Section 2.01(b) hereof. The term "DISSENTING
          HOLDER" shall mean a holder of Seller Common 

                                      B-3

<PAGE>   154

          Stock who has demanded appraisal rights in compliance with the
          applicable provisions of the MBCL concerning the right of such holder
          to dissent from the Merger and demand appraisal of such holder's
          shares of Seller Common Stock.

               (d) DISSENTER'S RIGHTS. Any Dissenting Holder (i) who files with
          the Seller a written objection to the Merger before the taking of the
          vote to approve this Plan of Merger by the shareholders of the Seller
          and who states in such objection that he intends to demand payment for
          his shares if the Merger is concluded and (ii) whose shares are not
          voted in favor of the Merger shall be entitled to demand payment for
          his shares of Seller Common Stock and an appraisal of the value
          thereof, in accordance with the provisions of Sections 86 through 98
          of the MBCL.

     2.02 ANTI-DILUTION. In the event that, subsequent to the date of this Plan
of Merger but prior to the Effective Time, the outstanding shares of Buyer
Common Stock or Seller Common Stock shall have been increased, decreased,
changed into or exchanged for a different number or kind of shares or securities
through reorganization, recapitalization, reclassification, stock dividend,
stock split, reverse stock split, or other like changes in the Buyer's or the
Seller's capitalization, other than pursuant to the Agreement, as the case may
be (a "RECAPITALIZATION"), then an appropriate and proportionate adjustment
shall be made to the Conversion Number so that each holder of Seller Common
Stock shall receive under Section 2.01(b) hereof the number of shares of Buyer
Common Stock (except for fractional shares) that such holder would have held
immediately following the Recapitalization if the Merger had occurred
immediately prior to the Recapitalization or the record date therefor, as
applicable. For purposes of this Section 2.02, in no event shall the issuance of
shares or securities by the Buyer in connection with the Buyer acquiring
directly or indirectly the stock or assets of any corporation, bank or other
entity be deemed to be a "Recapitalization".

     2.03 PROCEDURES.
          ----------

               (a) Certificates which represent shares of Seller Common Stock
          that are outstanding immediately prior to the Effective Time (a
          "CERTIFICATE") and are converted into shares of Buyer Common Stock
          pursuant to this Article II shall, after the Effective Time, be deemed
          to represent shares of Buyer Common Stock into which such shares have
          been converted and shall be exchangeable by the holders thereof in the
          manner provided in the transmittal materials described below for new
          certificates representing the shares of Buyer Common Stock into which
          such shares have been converted.

               (b) As promptly as practicable after the Effective Time, the
          Exchange Agent shall send to each holder of record of shares of Seller
          Common Stock outstanding at the Effective Time transmittal materials
          (which shall be reviewed with the Seller's counsel prior to the
          Effective Time) for use in exchanging the Certificates for such shares
          for certificates for shares of Buyer Common Stock into which such
          shares of Seller Common Stock have been converted pursuant to this
          Article II. Upon surrender of a Certificate, together with a duly
          executed letter of transmittal and any other required documents, the
          holder of such Certificate shall be entitled to receive, in exchange
          therefor, a certificate for the number of shares of Buyer Common Stock
          to which such holder is entitled pursuant to Section 2.01(b) hereof,
          and such Certificate shall forthwith be cancelled. No dividend or
          other distribution payable after the Effective Time with respect to
          Buyer Common Stock shall be paid to the holder of any unsurrendered
          Certificate until the holder thereof surrenders such Certificate, at
          which time such holder shall receive all dividends and distributions,
          without interest thereon, previously payable but withheld from such
          holder pursuant hereto. After the Effective Time, there shall be no
          transfers on the stock transfer books of the Seller of shares of
          Seller Common Stock which were issued and outstanding at the Effective
          Time and converted pursuant to the provisions of this Article II. If,
          after the Effective Time, Certificates are presented for transfer to
          the Seller, they shall be cancelled and exchanged 


                                      B-4
<PAGE>   155

          for the shares of Buyer Common Stock deliverable in respect thereof as
          determined in accordance with the provisions and procedures set forth
          in this Article II.

               (c) In lieu of the issuance of fractional shares of Buyer Common
          Stock pursuant to Sections 2.01(b) of this Plan of Merger, cash
          adjustments, without interest, will be paid to the holders of Seller
          Common Stock in respect of any fractional share that would otherwise
          be issuable and the amount of such cash adjustment shall be equal to
          an amount in cash determined by multiplying such holder's fractional
          interest by the "Average Price" of a share of Buyer Common Stock
          (rounded up to the nearest cent). The "CLOSING PRICE" of a share of
          Buyer Common Stock shall be the average of the last sale prices
          thereof as reported on the National Association of Securities Dealers
          Automated Quotation system over the ten (10) consecutive trading day
          period immediately preceding the date on which the last Requisite
          Regulatory Approval is received (without regard to any waiting period
          attached to the effectiveness thereof). For purposes of determining
          whether, and in what amounts, a particular holder of Seller Common
          Stock would be entitled to receive cash adjustments under this Section
          2.03(c), shares of record held by such holder and represented by two
          or more Certificates shall be aggregated.

               (d) After the Effective Time, holders of certificates of the
          Seller Common Stock (or its corporate predecessors in interest,
          including the Co-operative Bank of Concord or the Braintree Savings
          Bank) shall cease to be, and shall have no rights as, stockholders of
          the Seller, other than (i) to receive shares of Buyer Common Stock
          into which such shares have been converted and, if applicable,
          fractional share payments pursuant to the provisions hereof and (ii)
          the rights afforded to any Dissenting Holder (as defined in Section
          2.01(c)) under applicable provisions of the MBCL.

               (e) Notwithstanding the foregoing, neither the Buyer nor the
          Seller nor any other person shall be liable to any former holder of
          shares of Seller Common Stock for any shares or any dividends or
          distributions with respect thereto properly delivered to a public
          official pursuant to applicable abandoned property, escheat or similar
          laws.

               (f) In the event any Certificate shall have been lost, stolen or
          destroyed, upon receipt of appropriate evidence as to such loss, theft
          or destruction and to the ownership of such Certificate by the person
          claiming such Certificate to be lost, stolen or destroyed, and the
          receipt by the Buyer of appropriate and customary indemnification, the
          Buyer will issue in exchange for such lost, stolen or destroyed
          Certificate shares of Buyer Common Stock and the fractional share
          payment, if any, deliverable in respect thereof as determined in
          accordance with this Article II.

               (g) If any certificate representing shares of Buyer Common Stock
          is to be issued in a name other than that in which the Certificate
          surrendered in exchange therefor is registered, it shall be a
          condition of the issuance thereof that the Certificate so surrendered
          shall be properly endorsed (or accompanied by an appropriate
          instrument of transfer) and otherwise in proper form for transfer
          (including, but not limited to, that the signature of the transferor
          shall be properly guaranteed by a commercial bank, trust company,
          member firm of the NASD or other eligible guarantor institution), and
          that the person requesting such exchange shall pay to the Exchange
          Agent (as such term is defined in Section 4.01 hereof) in advance any
          transfer or other taxes required by reason of the issuance of a
          certificate representing shares of Buyer Common Stock in any name
          other than that of the registered holder of the Certificate
          surrendered, or required for any other reason, or shall establish to
          the satisfaction of the Exchange Agent that such tax has been paid or
          is not payable.

     2.04 CONVERSION OF OPTIONS. Each stock option (other than the Seller
Option) issued by the Seller to a third party, whether or not currently
exercisable, which entitles such third party to 

                                      B-5
<PAGE>   156


purchase Seller Common Stock, and which is outstanding and unexercised
immediately prior to the Effective Time, shall be converted into an option to
purchase shares of Buyer Common Stock, and the Buyer shall assume each such
option in accordance with the terms of the Seller stock option plan under which
it was granted and the stock option or other agreement by which it is evidenced,
with the following terms:

          (a) The number of shares of Buyer Common Stock shall be equal to the
     product of the number of shares of Seller Common Stock previously subject
     thereto and the Conversion Number, rounded down to the nearest whole share;
     and

          (b) The exercise price per share of Buyer Common Stock shall be equal
     to the exercise price per share of Seller Common Stock previously subject
     thereto divided by the Conversion Number, rounded up to the nearest cent;
     and

          (c) The duration and other terms of such Stock Option shall be
     unchanged except that all references to the Seller shall be deemed to be
     references to the Buyer; and

          (d) The Buyer shall assume the option as contemplated by Section
     424(a) of the Code; and

          (e) With respect to any stock option on Seller's Common Stock which is
     an incentive stock option within the meaning of Section 422 of the Internal
     Revenue Code of 1986, as amended, the Buyer shall take such actions (other
     than delaying the date the options on Buyer Common Stock become exercisable
     beyond the date on which such options would otherwise become exercisable
     pursuant to the relevant Seller Stock Plan) as may be necessary or
     appropriate to cause such option, upon being converted to an option on
     Buyer Common Stock, to remain such an incentive stock option.

                                   ARTICLE III

                            AMENDMENT AND TERMINATION
                            -------------------------

     3.01 TERMINATION. Notwithstanding the approval and adoption of this Plan of
Merger by the stockholders of the Seller, the Buyer and the Merger Subsidiary,
this Plan of Merger shall terminate forthwith in the event that the Agreement
shall be terminated as therein provided. In the event of the termination of this
Plan of Merger as provided above, this Plan of Merger shall forthwith become
null and void and there shall be no liability on the part of any of the parties
hereto except as otherwise provided in the Agreement.

     3.02 AMENDMENT. This Plan of Merger shall not be amended except by an
instrument in writing signed on behalf of each of the parties hereto pursuant to
an amendment to the Agreement approved in the manner therein provided. If any
such amendment to the Agreement is so approved, any amendment to this Plan of
Merger required by such amendment to the Agreement shall be effected by the
parties hereto by action taken by their respective Boards of Directors.

                                   ARTICLE IV

                                  MISCELLANEOUS
                                  -------------

     4.01 EXCHANGE AGENT. Prior to the Effective Time, the Buyer shall appoint
United States Trust Company, Boston, Massachusetts as exchange agent for the
purpose of exchanging certificates representing shares of Buyer Common Stock for
Certificates representing shares of Seller Common Stock (the "EXCHANGE AGENT"),
and the Buyer shall issue and deliver to the Exchange Agent certificates
representing shares of Buyer Common Stock and shall pay to the Exchange Agent
such 



                                      B-6
<PAGE>   157

amounts of cash as shall be required to be delivered to holders of shares of
Seller Common Stock in lieu of fractional shares of Buyer Common Stock, pursuant
to Article II of this Plan of Merger.

     4.02 COUNTERPARTS. This Plan of Merger may be executed in one or more
counterparts, all of which shall be considered one and the same agreement, and
shall become effective when one or more counterparts have been signed by each of
the parties and delivered to each of the other parties.

     4.03 GOVERNING LAW. This Plan of Merger shall be governed by and construed
in accordance with the laws of the Commonwealth of Massachusetts, without giving
effect to the principles of conflicts of laws thereof.

     IN WITNESS WHEREOF, the parties hereto have caused this Plan of Merger to
be duly executed and delivered as a sealed instrument as of the date first above
written.

                              UST CORP.

                              By:     /s/  Neal F. Finnegan
                                      -------------------------  
                                      President

                              By:     /s/  James K. Hunt
                                      -------------------------  
                                      Treasurer

                              WALDEN BANCORP, INC.

                              By:     /s/  David E. Bradbury
                                      -------------------------  
                                      President

                              By:     /s/  Michael O. Gilles
                                      -------------------------  
                                      Treasurer

                              MOSAIC CORP.

                              By:     /s/  Neal F. Finnegan
                                      -------------------------  
                                      President

                              By:     /s/  James K Hunt
                                      -------------------------  
                                      Treasurer


                                      B-7

<PAGE>   158


                                                                      APPENDIX C
                                                                      ----------

                             STOCK OPTION AGREEMENT

     STOCK OPTION AGREEMENT, dated as of August 30, 1996, between WALDEN
BANCORP, INC., a Massachusetts corporation (the "ISSUER") and UST CORP., a
Massachusetts corporation (the "GRANTEE").

     WHEREAS, the Grantee and the Issuer are entering into an Affiliation
Agreement and Plan of Reorganization of even date herewith (as amended and in
effect from time to time, the "ACQUISITION AGREEMENT"), which agreement is being
executed by the parties thereto simultaneously with this Agreement; and

     WHEREAS, as a condition to the Grantee's entry into the Acquisition
Agreement and in consideration for such entry, the Issuer has agreed to grant
the Grantee the Option (as hereinafter defined);

     NOW, THEREFORE, in consideration of the foregoing and the mutual covenants
and agreements set forth herein and in the Acquisition Agreement, the parties
hereto agree as follows:

     1. (a) The Issuer hereby grants to the Grantee an unconditional,
irrevocable option (the "OPTION") to purchase, subject to the terms hereof, up
to 1,016,868 fully paid and nonassessable shares (the "OPTION SHARES") of common
stock, no par value, of the Issuer ("COMMON STOCK") at a price of $20.50 per
share (the "OPTION PRICE"). The number of shares of Common Stock that may be
received upon the exercise of the Option and the Option Price are subject to
adjustment as herein set forth provided that in no event shall the number of
shares for which this Option is exercisable exceed 19.9% of the Issuer's issued
and outstanding shares of Common Stock (without giving effect to any shares of
Common Stock issued pursuant to the Option) less the number of shares previously
issued pursuant to exercise of the Option.

     (b) In the event that any additional shares of Common Stock are issued or
otherwise become outstanding after the date of this Agreement (other than
pursuant to exercise of the Option pursuant to this Agreement or as contemplated
by Section 5(a) of this Agreement), including, without limitation, pursuant to
stock option or other employee plans or as a result of the exercise of
conversion rights, the number of shares of Common Stock subject to the Option
shall be increased so that, after such issuance, it equals 19.9% of the number
of shares of Common Stock then issued and outstanding without giving effect to
any shares subject or issued pursuant to the Option. Nothing contained in this
Section 1(b) or elsewhere in this Agreement shall be deemed to authorize the
Issuer or the Grantee to breach any provision of the Acquisition Agreement.

     2. (a) The Holder (as such term is defined in paragraph (c) below) may
exercise the Option, in whole or part, if, but only if, both an Initial
Triggering Event (as defined in paragraph (e) below) and a Subsequent Triggering
Event (as defined in paragraph (f) below) shall have occurred prior to the
occurrence of an Exercise Termination Event (as defined in paragraph (b) below),
PROVIDED that the Holder shall have sent the written notice of such exercise (as
provided in paragraph (h) of this Section 2) within thirty (30) days following
such Subsequent Triggering Event and prior to the Exercise Termination Event.

     (b) The term "EXERCISE TERMINATION EVENT" shall mean the earliest of (i)
the Effective Time of the Merger, (ii) any termination of the Acquisition
Agreement in accordance with the provisions thereof if such termination occurs
prior to the occurrence of an Initial Triggering Event, and (iii) in the event
of any termination of the Acquisition Agreement in accordance with the





<PAGE>   159

provisions thereof after the occurrence of an Initial Triggering Event, the
passage of twelve (12) months after such termination. Notwithstanding the
termination of the Option, the Grantee shall be entitled to purchase those
Option Shares with respect to which it has exercised the Option in whole or in
part prior to the termination of the Option.

     (c) The term "HOLDER" shall mean the holder or holders of the Option.

     (d) The term "SCHEDULE 13G INVESTOR" shall mean any person holding voting
securities of the Issuer eligible to report the beneficial ownership of such
securities on Schedule 13G pursuant to the provisions of Rule 13d-1 under the
Exchange Act.

     (e) The term "INITIAL TRIGGERING EVENT" shall mean any of the following
events or transactions occurring after the date hereof:

          (i) The Issuer or any subsidiary of the Issuer, without having
     received the Grantee's prior written consent, shall have entered into an
     agreement to engage in an Acquisition Transaction with any Person (the term
     "PERSON" for purposes of this Agreement having the meaning assigned thereto
     in Sections 3(a)(9) and 13(d)(3) of the Exchange Act and the rules and
     regulations thereunder), other than the Grantee or any subsidiary of the
     Grantee, or, without the consent of the Grantee, the Board of Directors of
     the Issuer shall have approved an Acquisition Transaction or recommended
     that the shareholders of the Issuer approve or accept any Acquisition
     Transaction other than as contemplated by the Acquisition Agreement. For
     purposes of this Agreement, the term "ACQUISITION TRANSACTION" shall mean
     (A) a merger or consolidation, or any similar transaction, with the Issuer
     or any Significant Subsidiary of the Issuer, or any subsidiary of the
     Issuer which, after such transaction, would be a Significant Subsidiary of
     the Issuer, (B) a purchase, lease or other acquisition of all or
     substantially all of the assets of the Issuer or any Significant Subsidiary
     of the Issuer or (C) a purchase or other acquisition (including by way of
     merger, consolidation, share exchange or otherwise) of securities
     representing ten percent (10%) or more of the voting power of the Issuer or
     any Significant Subsidiary of the Issuer;

          (ii) The stockholders of the Issuer shall not have approved the
     Acquisition Agreement at the meeting of such stockholders held for the
     purpose of voting on the Acquisition Agreement, such meeting shall not have
     been held or shall have been canceled prior to the termination of the
     Acquisition Agreement, or the Issuer's Board of Directors shall have
     withdrawn or modified in a manner adverse to the Grantee the recommendation
     of the Issuer's Board of Directors with respect to the Acquisition
     Agreement, in each case after; (A), any Person, other than the Grantee or
     any subsidiary of the Grantee or the Issuer in a fiduciary capacity, and
     other than a Schedule 13G Investor, shall have acquired beneficial
     ownership (as hereinafter defined) or the right to acquire beneficial
     ownership of ten percent (10%) or more of the outstanding shares of Common
     Stock if such Person owned beneficially less than ten percent (10%) of the
     outstanding shares of Common Stock on the date of this Agreement, or any
     Person shall have acquired beneficial ownership of an additional three
     percent (3%) of the outstanding shares of Common Stock if such Person owned
     beneficially ten percent (10%) or more of the outstanding shares of Common
     Stock on the date of this Agreement (the term "BENEFICIAL OWNERSHIP" for
     purposes of this Agreement having the meaning assigned thereto in Section
     13(d) of the Exchange Act, and in the rules and regulations thereunder);
     (B), any Person, other than the Grantee or any subsidiary of the Grantee,
     shall have made a bona-fide proposal to the Issuer or its shareholders to
     engage in an Acquisition Transaction by public announcement or written
     communication that shall be or become the subject of public disclosure; or
     (C), any Person other than the Grantee or any Subsidiary of the Grantee,
     other than in connection with a transaction to which the Grantee has given
     its prior written consent, shall have filed an application or 

                                      C-2

<PAGE>   160


     notice with the Federal Reserve Board or other federal or state bank
     regulatory authority, which application or notice has been accepted for
     processing, for approval to engage in an Acquisition Transaction;

          (iii) After any Person other than the Grantee or any subsidiary of the
     Grantee has made a proposal to the Issuer or its shareholders to engage in
     an Acquisition Transaction, the Issuer shall have breached any covenant or
     obligation contained in the Acquisition Agreement and such breach (A) would
     entitle the Grantee to terminate the Acquisition Agreement and (B) shall
     not have been remedied prior to the Notice Date (as defined in paragraph
     (h) below); or

          (iv) Any person (other than Grantee or any Subsidiary of Grantee)
     shall have commenced (as such term is defined in Rule 14d-2 under the
     Exchange Act) or shall have filed a registration statement under the
     Securities Act of 1933, as amended (the "Securities Act"), with respect to,
     a tender offer or exchange offer to purchase any shares of Issuer Common
     Stock such that, upon consummation of such offer, such person would own or
     control 25% or more of the then outstanding shares of Issuer Common Stock
     (such an offer being referred to herein as a "Tender Offer" or an "Exchange
     Offer," respectively).

     (f) The term "SUBSEQUENT TRIGGERING EVENT" shall mean either of the
following events or transactions occurring after the date hereof:

          (i) The acquisition by any Person (other than a Schedule 13G Investor)
     of beneficial ownership of twenty-five percent (25%) or more of the then
     outstanding Common Stock; or

          (ii) The occurrence of the Initial Triggering Event described in
     subparagraph (i) of paragraph (e) of this Section 2, except that the
     percentage referenced in clause (C) thereof shall be twenty-five percent
     (25%) in lieu of ten percent (10%).

     (g) The Issuer shall notify the Grantee promptly in writing of the
occurrence of any Initial Triggering Event or Subsequent Triggering Event
(together, a "TRIGGERING EVENT"), it being understood that the giving of such
notice by the Issuer shall not be a condition to the right of the Holder to
exercise the Option.

     (h) In the event the Holder is entitled to and wishes to exercise the
Option, it shall send to the Issuer a written notice (the date of which being
herein referred to as the "NOTICE DATE") specifying (i) the total number of
shares of Common Stock it will purchase pursuant to such exercise, and (ii) a
place and date not earlier than three (3) business days nor later than
forty-five (45) business days from the Notice Date for the closing of such
purchase (the "CLOSING"); PROVIDED that if prior notification to or approval of
the Federal Reserve Board or any other regulatory agency is required in
connection with such purchase, the Holder shall promptly file the required
notice or application for approval and shall expeditiously process the same and
the period of time that otherwise would run pursuant to this sentence shall run
instead from the date on which any required notification periods have expired or
been terminated or such approvals have been obtained and any requisite waiting
period or periods shall have passed. The term "business day" for purposes of
this Agreement means any day, excluding Saturdays, Sundays and any other day
that is a legal holiday in the Commonwealth of Massachusetts or a day on which
banking institutions in the Commonwealth of Massachusetts are authorized by law
or executive order to close.

     (i) At the Closing, the Holder shall pay to the Issuer the aggregate
purchase price for the shares of Common Stock purchased pursuant to the exercise
of the Option in immediately available funds by a wire transfer to a bank
account designated by the Issuer, PROVIDED that failure or refusal of the Issuer
to designate such a bank account shall not preclude the Holder from exercising
the Option.


                                      C-3

<PAGE>   161

     (j) At such Closing, simultaneously with the delivery of immediately
available funds as provided in paragraph (i) above, the Issuer shall deliver to
the Holder a certificate or certificates representing the number of shares of
Common Stock purchased by the Holder and, if the Option should be exercised in
part only, a new Option evidencing the rights of the Holder thereof to purchase
the balance of the shares purchasable hereunder, and the Holder shall deliver to
the Issuer a copy of this Agreement and a letter agreeing that the Holder will
not offer to sell or otherwise dispose of such shares in violation of applicable
law or the provisions of this Agreement.

     (k) Certificates for the Common Stock delivered at a Closing hereunder may
(in the sole discretion of the Issuer) be endorsed with a restrictive legend
that shall read substantially as follows:

     "THE TRANSFER OF THE SHARES REPRESENTED BY THIS CERTIFICATE IS SUBJECT TO
     RESTRICTION PURSUANT TO THE TERMS OF A STOCK OPTION AGREEMENT DATED AS OF
     AUGUST 30, 1996, A COPY OF WHICH AGREEMENT WILL BE PROVIDED TO THE HOLDER
     HEREOF WITHOUT CHARGE UPON RECEIPT BY THE ISSUER OF A WRITTEN REQUEST
     THEREFOR."

It is understood and agreed that the above legend shall be removed by delivery
of substitute certificate(s) without such legend if the shares have been sold or
transferred in compliance with the provisions of this Agreement and under
circumstances that do not require the retention of such legend. In addition,
such certificates shall bear any other legend as may be required by law.

     (l) Upon the giving by the Holder to the Issuer of the written notice of
exercise of the Option provided for under paragraph (h) above, the tender of the
applicable purchase price in immediately available funds and the tender of a
copy of this Agreement to the Issuer, such Holder shall be deemed to be the
holder of record of the shares of Common Stock issuable upon such exercise,
notwithstanding that the stock transfer books of the Issuer shall then be closed
or that certificates representing such shares of Common Stock shall not then be
actually delivered to the Holder. The Issuer shall pay all expenses, and any and
all United States federal, state and local taxes and other charges that may be
payable in connection with the preparation, issue and delivery of stock
certificates under this Section 2 in the name of the Holder or its assignee,
transferee or designee.

     3. The Issuer agrees (a) that it shall at all times maintain, free from
preemptive rights, sufficient authorized but unissued or treasury shares of
Common Stock so that the Option may be exercised without requiring the Issuer's
stockholders to approve an increase in the number of authorized shares of Common
Stock after giving effect to all other options, warrants, convertible securities
and other rights to purchase Common Stock, (b) that it will not, by charter
amendment or through reorganization, consolidation, merger, dissolution or sale
of assets, or by any other voluntary act, avoid or seek to avoid the observance
or performance of any of the covenants, stipulations or conditions to be
observed or performed hereunder by the Issuer, (c) promptly to take all action
as may from time to time be required (including without limitation cooperating
fully with any Holders in preparing any applications or notices required under
the Bank Holding Company Act of 1956, as amended, or the Change in Bank Control
Act of 1978, as amended, or any state banking law), in order to permit such
Holders to exercise the Option and the Issuer duly and effectively to issue
shares of Common Stock pursuant hereto, and (d) promptly to take all action
provided herein to protect the rights of any Holders against dilution.

     4. This Agreement (and the Option granted hereby) is exchangeable, without
expense, at the option of each Holder, upon presentation and surrender of this
Agreement at the principal office of the Issuer, for other Agreements providing
for Options of different denominations entitling the Holder thereof to purchase,
on the same terms and subject to the same conditions as are set forth herein, in
the aggregate the same number of shares of Common Stock purchasable hereunder.



                                      C-4
<PAGE>   162

The terms "AGREEMENT" and "OPTION" as used herein include any Stock Option
Agreements and related Options for which this Agreement (and the Option granted
hereby) may be exchanged. Upon receipt by the Issuer of evidence reasonably
satisfactory to it of the loss, theft, destruction or mutilation of this
Agreement, and (in the case of loss, theft or destruction) of reasonably
satisfactory indemnification, and upon surrender and cancellation of this
Agreement, if mutilated, the Issuer will execute and deliver a new Agreement of
like tenor and date. Any such new Agreement executed and delivered shall
constitute for all purposes and under all circumstances a contractual obligation
on the part of the Issuer, whether or not this Agreement so lost, stolen,
destroyed or mutilated shall at any time be enforceable by anyone.

     5. In addition to the adjustment in the number of Option Shares pursuant to
Section 1 of this Agreement, the number of Option Shares shall be subject to
adjustment from time to time as provided in this Section 5.

     (a) (i) In the event of any change in the shares of Common Stock by reason
     of stock dividend, split up, merger, recapitalization, subdivision,
     conversion, combination, exchange of shares or similar transaction, the
     type and number of Option Shares, and the Option Price therefor, shall be
     adjusted appropriately, and proper provision shall be made in the
     agreements governing such transaction, so that the Grantee shall receive
     upon exercise of the Option the number and class of shares or other
     securities or property that the Grantee would have held immediately after
     such event if the Option had been exercised immediately prior to such
     event, or the record date therefor, as applicable.

          (ii) The Issuer may make such increases in the number of Option
     Shares, in addition to those required under subparagraph (a)(i) above, as
     shall be determined by its Board of Directors to be advisable in order to
     avoid taxation, so far as practicable, of any dividend of stock or stock
     rights or any event treated as such for federal income tax purposes to the
     recipients.

     (b) Whenever the number of Option Shares (or other securities) purchasable
upon exercise hereof is adjusted as provided in this Section 5, the Option Price
shall be adjusted by multiplying the Option Price by a fraction, the numerator
of which is equal to the number of Option Shares prior to the adjustment and the
denominator of which is equal to the number of Option Shares (or other
securities) purchasable after the adjustment.

     6. Upon the occurrence of a Subsequent Triggering Event that occurs prior
to an Exercise Termination Event, Issuer shall, at the request of Grantee
delivered within thirty (30) days of such Subsequent Triggering Event (whether
on the Grantor's own behalf or on the behalf of any subsequent Holder of this
Option (or part thereof) or any of the shares of Common Stock issued pursuant
hereto), promptly prepare, file and keep current, with respect to the Option and
the Option Shares, a "shelf" registration statement under Rule 415 of the
Securities Act or any successor provision, and Issuer shall use its best efforts
to qualify such shares under any applicable state securities laws. Issuer will
use its best efforts to cause such registration statement first to become
effective and then to remain effective for such period not in excess of 180 days
from the day such registration statement first becomes effective or such shorter
time as may be reasonably necessary to effect sales or other dispositions of
Option Shares. Grantee shall have the right to demand two such registrations.
Any registration statement prepared and filed under this Section 6, and any
sales covered thereby, shall be at Issuer's expense, except for underwriting
discounts or commissions, broker's fees and expenses and the fees and
disbursements of Grantee's counsel related thereto. The foregoing
notwithstanding, if, at the time of any request by Grantee for registration of
the Option or Option Shares as provided above, Issuer is in registration with
respect to an underwritten public offering of shares of Common Stock, and if in
the good faith judgment of the managing underwriter or managing underwriters,
or, if none, the sole underwriter or underwriters, of such offering, the
inclusion of the Option or Option Shares would interfere with the 

                                      C-5
<PAGE>   163
successful marketing of the shares represented by the Option the number of
Option Shares otherwise to be covered in the registration statement contemplated
hereby may be reduced; PROVIDED, HOWEVER, that if such reduction occurs, the
Issuer shall file a registration statement for the balance as promptly as
practical and no reduction shall thereafter occur. Each such Holder shall
provide all information reasonably requested by Issuer for inclusion in any
registration statement to be filed hereunder. If requested by any such Holder in
connection with such registration, Issuer shall become a party to any
underwriting agreement relating to the sale of such shares, but only to the
extent of obligating itself in respect of representations, warranties,
indemnities and other agreements customarily included in such underwriting
agreements for the Issuer.

     7. (a) Upon the occurrence of a Subsequent Triggering Event that occurs
prior to an Exercise Termination Event, (i) at the request of any Holder,
delivered within thirty (30) days following such occurrence (or such later
period as provided in Section 10), the Issuer shall repurchase the Option from
the Holder at a price (the "OPTION REPURCHASE PRICE") equal to the amount by
which (A) the market/offer price (as defined below) exceeds (B) the Option
Price, multiplied by the number of shares for which this Option may then be
exercised, plus, to the extent not previously reimbursed, the Grantee's
reasonable out-of-pocket expenses incurred in connection with the transactions
contemplated by, and the enforcement of the Grantee's rights under, the
Acquisition Agreement, including without limitation legal, accounting and
investment banking fees (the "GRANTEE'S OUT-OF-POCKET EXPENSES"), and (ii) at
the request of any owner of Option Shares from time to time (the "OWNER"),
delivered within thirty (30) days following such occurrence (or such later
period as provided in Section 10), the Issuer shall repurchase such number of
the Option Shares from such Owner as the Owner shall designate at a price per
share ("OPTION SHARE REPURCHASE PRICE") equal to the greater of (A) the
market/offer price and (B) the average exercise price per share paid by the
Owner for the Option Shares so designated, plus, to the extent not previously
reimbursed, the Grantee's Out-of-Pocket Expenses. The term "MARKET/OFFER PRICE"
shall mean the highest of (w) the price per share of the Common Stock at which a
tender offer or exchange offer therefor has been made, (x) the price per share
of the Common Stock to be paid by any Person, other than the Grantee or a
subsidiary of the Grantee, pursuant to an agreement with the Issuer, (y) the
highest closing price for shares of Common Stock within the six (6) month period
immediately preceding the required repurchase of Options or Option Shares, as
the case may be, or (z) in the event of a sale of all or substantially all of
the Issuer's assets, the sum of the price paid in such sale for such assets and
the current market value of the remaining assets of the Issuer as determined by
a nationally recognized investment banking firm selected by a majority in the
interest of the Holders or the Owners, as the case may be, and reasonably
acceptable to the Issuer, divided by the number of shares of Common Stock of the
Issuer outstanding at the time of such sale. In determining the market/offer
price, the value of consideration other than cash shall be determined by a
nationally recognized investment banking firm selected by a majority in interest
of the Holders or the Owners, as the case may be, and reasonably acceptable to
the Issuer.

     (b) Each Holder and Owner, as the case may be, may exercise its right to
require the Issuer to repurchase the Option and any Option Shares pursuant to
this Section 7 by surrendering for such purpose to the Issuer, at its principal
office, a copy of this Agreement or certificates for Option Shares, as
applicable, accompanied by a written notice or notices stating that such Holder
or Owner elects to require the Issuer to repurchase this Option and/or Option
Shares in accordance with the provisions of this Section 7. As promptly as
practicable, and in any event within ten (10) business days after the surrender
of the Option and/or certificates representing Option Shares and the receipt of
such notice or notices relating thereto, the Issuer shall deliver or cause to be
delivered to each Holder the Option Repurchase Price and/or to each Owner the
Option Share Repurchase Price therefor or the portion thereof that the Issuer is
not then prohibited under applicable law and regulation from so delivering.

     (c) To the extent that the Issuer is prohibited under applicable law or
regulation, or as a consequence of administrative policy, or as a result of a
written agreement or other binding 

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<PAGE>   164

obligation with a governmental or regulatory body or agency, from repurchasing
the Option and/or the Option Shares in full, the Issuer shall immediately so
notify each Holder and/or each Owner and thereafter deliver or cause to be
delivered, from time to time, to such Holder and/or Owner, as appropriate, the
portion of the Option Repurchase Price and the Option Share Repurchase Price,
respectively, that it is no longer prohibited from delivering, within ten (10)
business days after the date on which the Issuer is no longer so prohibited;
PROVIDED, HOWEVER, that if the Issuer at any time after delivery of a notice of
repurchase pursuant to paragraph (b) of this Section 7 is prohibited under
applicable law or regulation, or as a consequence of administrative policy, from
delivering to any Holder and/or Owner, as appropriate, the Option Repurchase
Price and the Option Share Repurchase Price, respectively, in part or in full
(and the Issuer hereby undertakes to use its best efforts to receive all
required regulatory and legal approvals and to file any required notices as
promptly as practicable in order to accomplish such repurchase), such Holder or
Owner may revoke its notice of repurchase of the Option or the Option Shares
either in whole or to the extent of the prohibition, whereupon the Issuer shall
promptly (i) deliver to such Holder and/or Owner, as appropriate, that portion
of the Option Purchase Price or the Option Share Repurchase Price that the
Issuer is not prohibited from delivering; and (ii) deliver, as appropriate,
either (A) to such Holder, a new Stock Option Agreement evidencing the right of
such Holder to purchase that number of shares of Common Stock obtained by
multiplying the number of shares of Common Stock for which the surrendered Stock
Option Agreement was exercisable at the time of delivery of the notice of
repurchase by a fraction, the numerator of which is the Option Repurchase Price
less the portion thereof theretofore delivered to the Holder and the denominator
of which is the Option Repurchase Price, or (B) to such Owner, a certificate for
the Option Shares it is then so prohibited from repurchasing.

     8. (a) In the event that prior to an Exercise Termination Event, the Issuer
shall enter into an agreement (i) to consolidate with or merge into any Person,
other than the Grantee or one of the Grantee's subsidiaries, and the Issuer
shall not be the continuing or surviving corporation of such consolidation or
merger, (ii) to permit any Person, other than the Grantee or one of its
subsidiaries, to merge into the Issuer and the Issuer shall be the continuing or
surviving corporation, but, in connection with such merger, the then outstanding
shares of Common Stock shall be changed into or exchanged for stock or other
securities of any other Person or cash or any other property, or the then
outstanding shares of Common Stock shall, after such merger, represent less than
fifty percent (50%) of the outstanding shares and share equivalents of the
merged company, or (iii) to sell or otherwise transfer all or substantially all
of its assets to any Person, other than the Grantee or one of the Grantee's
subsidiaries, then, and in each such case, the agreement governing such
transaction shall make proper provision so that the Option shall upon the
consummation of any such transaction and upon the terms and conditions set forth
herein, be converted into, or exchanged for, an option (the "SUBSTITUTE
OPTION"), at the election of the Holder, of either (A) the Acquiring Corporation
(as defined in paragraph (b) below) or (B) any Person that controls the
Acquiring Corporation.

          (b) The following terms have the meanings indicated:

          (i) The term "ACQUIRING CORPORATION" shall mean (A) the continuing or
     surviving corporation of a consolidation or merger with the Issuer (if
     other than the Issuer), (B) the Issuer in a merger in which the Issuer is
     the continuing or surviving Person, and (C) the transferee of all or
     substantially all of the Issuer's assets.

          (ii) The term "SUBSTITUTE COMMON STOCK" shall mean the common stock
     issued by the issuer of the Substitute Option upon exercise of the
     Substitute Option.

          (iii) The term "ASSIGNED VALUE" shall mean the "market/offer price",
     as defined in paragraph (a) of Section 7 hereof.


                                      C-7
<PAGE>   165

          (iv) The term "AVERAGE PRICE" shall mean the average closing price of
     a share of the Substitute Common Stock for the one (1) year period
     immediately preceding the consolidation, merger or sale in question, but in
     no event higher than the closing price of the shares of the Substitute
     Common Stock on the day preceding such consolidation, merger or sale,
     PROVIDED that if the Issuer is the issuer of the Substitute Option, the
     Average Price shall be computed with respect to a share of common stock
     issued by the Person merging into the Issuer or by any company which
     controls such Person, as the Holder may elect.

     (c) The Substitute Option shall have the same terms as the Option, PROVIDED
that if the terms of the Substitute Option cannot, for legal reasons, be the
same as the Option, such terms shall, to the extent legally permissible, be as
similar as possible to, and in no event less advantageous to the Holder than,
the terms of the Option. The issuer of the Substitute Option shall also enter
into an agreement with the then Holder or Holders of the Substitute Option in
substantially the same form as this Agreement, which shall be applicable to the
Substitute Option.

     (d) The Substitute Option shall be exercisable for such number of shares of
the Substitute Common Stock as is equal to (i) the product of (A) the Assigned
Value and (B) the number of shares of Common Stock for which the Option is then
exercisable, divided by (ii) the Average Price. The exercise price of the
Substitute Option per share of the Substitute Common Stock shall then be equal
to the Option Price multiplied by a fraction in which the numerator is the
number of Option Shares and the denominator is the number of shares of the
Substitute Common Stock for which the Substitute Option is exercisable.

     (e) In no event, pursuant to any of the foregoing paragraphs, shall the
Substitute Option be exercisable for more than 19.9% of the aggregate of the
shares of the Substitute Common Stock outstanding prior to exercise of the
Substitute Option (without giving effect to any shares of Substitute Common
Stock issued pursuant to the Substitute Option) less the number of shares
previously issued pursuant to the Substitute Option. In the event that the
Substitute Option would be exercisable for more than 19.9% of the shares of
Substitute Common Stock outstanding prior to exercise but for this paragraph
(e), the issuer of the Substitute Option (THE "SUBSTITUTE OPTION ISSUER") shall
make a cash payment to the Holder equal to the excess of (i) the value of the
Substitute Option without giving effect to the limitation in this paragraph (e)
over (ii) the value of the Substitute Option after giving effect to the
limitation in this paragraph (e). The difference in value shall be determined by
a nationally recognized investment banking firm selected by a majority in
interest of the Holders or the Owners, as the case may be.

     (f) The Issuer shall not enter into any transaction described in paragraph
(a) of this Section 8 unless the Acquiring Corporation and any Person that
controls the Acquiring Corporation shall have assumed in writing all the
obligations of the Issuer hereunder.

     9. (a) At the written request of the holder of the Substitute Option (the
"SUBSTITUTE OPTION HOLDER"), the issuer of the Substitute Option (the
"SUBSTITUTE OPTION ISSUER") shall repurchase the Substitute Option from the
Substitute Option Holder at a price (the "SUBSTITUTE OPTION REPURCHASE PRICE")
equal to the amount by which (i) the Highest Closing Price (as hereinafter
defined) exceeds (ii) the exercise price of the Substitute Option, multiplied by
the number of shares of the Substitute Common Stock for which the Substitute
Option may then be exercised, PLUS to the extent not previously reimbursed, the
Grantee's Out-of-Pocket Expenses, and at the request of each owner (the
"SUBSTITUTE SHARE OWNER") of shares of the Substitute Common Stock (the
"SUBSTITUTE SHARES"), the Substitute Option Issuer shall repurchase the
Substitute Shares at a price per share (the "SUBSTITUTE SHARE REPURCHASE PRICE")
equal to the greater of (A) the Highest Closing Price and (B) the average
exercise price per share paid by the Substitute Share Owner for the Substitute
Shares so designated, plus, to the extent not previously reimbursed, the
Grantee's Out-of-Pocket Expenses. The term "HIGHEST CLOSING PRICE" shall mean
the highest closing price for shares of the Substitute Common Stock within the
six (6) month period immediately preceding the 


                                      C-8
<PAGE>   166

date the Substitute Option Holder gives notice of the required repurchase of the
Substitute Option or the Substitute Share Owner gives notice of the required
repurchase of the Substitute Shares, as applicable.

     (b) Each Substitute Option Holder and the Substitute Share Owner, as the
case may be, may exercise its respective right to require the Substitute Option
Issuer to repurchase the Substitute Option and the Substitute Shares pursuant to
this Section 9 by surrendering for such purpose to the Substitute Option Issuer,
at its principal office, the agreement for such Substitute Option (or, in the
absence of such an agreement, a copy of this Agreement) and certificates for
Substitute Shares accompanied by a written notice or notices stating that such
Substitute Option Holder or Substitute Share Owner elects to require the
Substitute Option Issuer to repurchase the Substitute Option and/or the
Substitute Shares in accordance with the provisions of this Section 9. As
promptly as practicable, and in any event within five (5) business days after
the surrender of the Substitute Option and/or the certificates representing
Substitute Shares and the receipt of such notice or notices relating thereto,
the Substitute Option Issuer shall deliver or cause to be delivered to the
Substitute Option Holder the Substitute Option Repurchase Price and/or to the
Substitute Share Owner the Substitute Share Repurchase Price therefor, or the
portion(s) thereof which the Substitute Option Issuer is not then prohibited
under applicable law and regulation from so delivering.

     (c) To the extent that the Substitute Option Issuer is prohibited under
applicable law or regulation, or as a consequence of administrative policy, or
as a result of a written agreement or other binding obligation with a
governmental or regulatory body or agency, from repurchasing the Substitute
Option and/or the Substitute Shares in full, the Substitute Option Issuer shall
immediately so notify each Substitute Option Holder and/or the Substitute Share
Owner and thereafter deliver or cause to be delivered, from time to time, to the
Substitute Option Holder and/or Substitute Share Owner, as appropriate, that
portion of the Substitute Option Repurchase Price and the Substitute Share
Repurchase Price, respectively, which it is no longer prohibited from
delivering, within five (5) business days after the date on which the Substitute
Option Issuer is no longer so prohibited, PROVIDED, HOWEVER, that if the
Substitute Option Issuer is, at any time after delivery of a notice of
repurchase pursuant to paragraph (b) of this Section 9 prohibited under
applicable law or regulation, or as a consequence of administrative policy, or
as a result of a written agreement or other binding obligation with a
governmental or regulatory body or agency, from delivering to the Substitute
Option Holder and/or the Substitute Share Owner, as appropriate, the Substitute
Option Repurchase Price and the Substitute Share Repurchase Price, respectively,
in part or in full (and the Substitute Option Issuer shall use its best efforts
to receive all required regulatory and legal approvals as promptly as
practicable in order to accomplish such repurchase), the Substitute Option
Holder or Substitute Share Owner may revoke its notice of repurchase of the
Substitute Option or the Substitute Shares either in whole or to the extent of
the prohibition, whereupon the Substitute Option Issuer shall promptly (i)
deliver to the Substitute Option Holder or Substitute Share Owner, as
appropriate, that portion of the Substitute Option Repurchase Price or the
Substitute Share Repurchase Price that the Substitute Option Issuer is not
prohibited from delivering; and (ii) deliver, as appropriate, either (A) to the
Substitute Option Holder, a new Substitute Option evidencing the right of the
Substitute Option Holder to purchase that number of shares of the Substitute
Common Stock obtained by multiplying the number of shares of the Substitute
Common Stock for which the surrendered Substitute Option was exercisable at the
time of delivery of the notice of repurchase by a fraction, the numerator of
which is the Substitute Option Repurchase Price less the portion thereof
theretofore delivered to the Substitute Option Holder and the denominator of
which is the Substitute Option Repurchase Price, or (B) to the Substitute Share
Owner, a certificate for the Substitute Option Shares it is then so prohibited
from repurchasing.

     10. The thirty (30) day period for exercise of certain rights under
Sections 2, 6, 7 and 12 hereof shall be extended in each such case: (i) to the
extent necessary to obtain all regulatory approvals for the exercise of such
rights and for the expiration of all statutory waiting periods; and 


                                      C-9

<PAGE>   167
(ii) to the extent necessary to avoid liability under Section 16(b) of the
Exchange Act by reason of such exercise, PROVIDED that notice of intent to
exercise such rights shall be given to the Issuer within the requisite thirty
(30) day period and the Grantee and the Holders shall use their best efforts to
promptly obtain all requisite approvals and cause the expiration of all
requisite waiting periods.

     11. The Issuer hereby represents and warrants to the Grantee as follows:

     (a) The Issuer has full corporate power and authority to execute and
deliver this Agreement and to consummate the transactions contemplated hereby.
The execution and delivery of this Agreement and the consummation of the
transactions contemplated hereby have been duly and validly authorized by the
Board of Directors of the Issuer and no other corporate proceedings on the part
of the Issuer are necessary to authorize this Agreement or to consummate the
transactions so contemplated. This Agreement has been duly and validly executed
and delivered by the Issuer. This Agreement is the valid and legally binding
obligation of the Issuer, enforceable against the Issuer in accordance with its
respective terms, except that enforcement thereof may be limited by the
receivership, conservatorship and supervisory powers of bank regulatory agencies
generally as well as bankruptcy, insolvency, reorganization, moratorium or other
similar laws affecting enforcement of creditors rights generally and except that
enforcement thereof may be subject to general principles of equity (regardless
of whether enforcement is considered in a proceeding in equity or at law) and
the availability of equitable remedies.

     (b) The Issuer has taken all necessary corporate action to authorize and
reserve and to permit it to issue, and at all times from the date hereof through
the termination of this Agreement in accordance with its terms will have
reserved for issuance upon the exercise of the Option, that number of shares of
Common Stock equal to the maximum number of shares of Common Stock at any time
and from time to time issuable hereunder, and all such shares, upon issuance
pursuant hereto, will be duly authorized, validly issued, fully paid,
nonassessable, and will be delivered free and clear of all claims, liens,
encumbrances and security interests and not subject to any preemptive rights.

     12. Neither of the parties hereto may assign any of its rights or
obligations under this Option Agreement or the Option created hereunder to any
other Person, whether by operation of law or otherwise, without the express
written consent of the other party, except that in the event a Subsequent
Triggering Event shall have occurred prior to an Exercise Termination Event, the
Grantee may, subject to the right of first refusal set forth in Section 13,
assign, transfer or sell in whole or in part its rights and obligations
hereunder within thirty (30) days following such Subsequent Triggering Event (or
such later period as provided in Section 10); PROVIDED, HOWEVER, that in the
event the Grantee sells, assigns or transfers all or a portion of the Option to
other Holders as permitted by this Agreement, the Grantee may exercise its
rights hereunder on behalf of itself and such Holders.

     13. If at any time after the occurrence of a Subsequent Triggering Event
and, with respect to shares of Common Stock or other securities acquired by the
Grantee pursuant to an exercise of the Option, prior to the expiration of
twenty-four (24) months after the expiration of the Option pursuant to Section
2(b), the Grantee shall desire to sell, assign, transfer or otherwise dispose of
the Option, in whole or in part, or all or any of the shares of Common Stock or
other securities acquired by the Grantee pursuant to the Option, the Grantee
shall give the Issuer written notice of the proposed transaction (an "OFFEROR'S
NOTICE"), identifying the proposed transferee, accompanied by a copy of a
binding offer to purchase the Option or such shares or other securities signed
by such transferee and setting forth the terms of the proposed transaction. An
Offeror's Notice shall be deemed an offer by the Grantee to the Issuer, which
may be accepted within ten (10) business days of the receipt of such Offeror's
Notice, on the same terms and conditions and at the same price at which the
Grantee is proposing to transfer the Option or such shares or 

                                      C-10

<PAGE>   168

other securities to such transferee. The purchase of the Option or such shares
or other securities by the Issuer shall be settled within five (5) business days
of the date of the acceptance of the offer and the purchase price shall be paid
to the Grantee in immediately available funds, PROVIDED that, if prior
notification to or approval, consent or waiver of the Federal Reserve Board or
any other regulatory authority is required in connection with such purchase, the
Issuer shall promptly file the required notice or application for approval,
consent or waiver and shall expeditiously process the same (and the Grantee
shall cooperate with the Issuer in the filing of any such notice or application
and the obtaining of any such approval) and the period of time that otherwise
would run pursuant to this sentence shall run instead from the date on which, as
the case may be, (a) the required notification period has expired or been
terminated or (b) such approval has been obtained and, in either event, any
requisite waiting period shall have passed. In the event of the failure or
refusal of the Issuer to purchase the Option or the shares or other securities,
as the case may be, covered by an Offeror's Notice or if the Federal Reserve
Board or any other regulatory authority disapproves the Issuer's proposed
purchase of the Option or such shares or other securities, the Grantee may,
within sixty (60) days following the date of the Offeror's Notice (subject to
any necessary extension for regulatory notification, approval, or waiting
periods), sell all, but not less than all, of the portion of the Option (which
may be one hundred percent (100%)) or such shares or other securities, as the
case may be, proposed to be transferred to the proposed transferee identified in
the Offeror's Notice at no less than the price specified and on terms no more
favorable to the proposed transferee than those set forth in the Offeror's
Notice. The requirements of this Section 13 shall not apply to (i) any
disposition of the Option or any shares of Common Stock or other securities by a
Person to whom the Grantee has assigned its rights under the Option with the
prior written consent of the Issuer, (ii) any sale by means of a public offering
in which steps are taken to reasonably ensure that no purchaser will acquire
securities representing more than five percent (5%) of the outstanding shares of
Common Stock of the Issuer or (iii) any transfer to a direct or indirect
wholly-owned subsidiary of the Grantee which agrees in writing to be bound by
the terms hereof.

     14. Each of the Grantee and the Issuer will use all reasonable efforts to
make all filings with, and to obtain consents of, all third parties and
governmental authorities necessary to the consummation of the transactions
contemplated by this Agreement, including without limitation applying to the
Federal Reserve Board under the Bank Holding Company Act of 1956, as amended,
for approval to acquire the shares issuable hereunder.

     15. Notwithstanding anything to the contrary herein, in the event that the
Holder or the Owner or any Related Person thereof (as hereinafter defined) is a
Person making an offer or proposal to engage in an Acquisition Transaction
(other than the transaction contemplated by the Acquisition Agreement), then (a)
in the case of a Holder or any Related Person thereof, the Option held by it
shall immediately terminate and be of no further force or effect, and (b) in the
case of an Owner or any Related Person thereof, the Option Shares held by it
shall be immediately repurchasable by the Issuer at the Option Price. For
purposes of this Agreement, a "RELATED PERSON" of a Holder or Owner means any
Affiliate (as defined in Rule 12b-2 of the rules and regulations under the
Exchange Act) of the Holder or the Owner and any Person that is required to file
a Schedule 13D with the Holder or the Owner with respect to shares of Common
Stock or options to acquire the Common Stock.

     16. The parties hereto acknowledge that damages would be an inadequate
remedy for a breach of this Agreement by either party hereto and that the
obligations of the parties hereto shall be enforceable by either party hereto
through injunctive or other equitable relief.

     17. If any term, provision, covenant or restriction contained in this
Agreement is held by a court or a federal or state regulatory agency of
competent jurisdiction to be invalid, void or unenforceable, the remainder of
the terms, provisions and covenants and restrictions contained in this Agreement
shall remain in full force and effect, and shall in no way be affected, impaired
or invalidated. If for any reason such court or regulatory agency determines
that the Holder is not 



                                      C-11

<PAGE>   169

permitted to acquire, or the Issuer is not permitted to repurchase pursuant to
Section 7, the full number of shares of Common Stock provided in Section 1(a)
hereof (as adjusted pursuant to Sections 1(b) or 5 hereof), it is the express
intention of the Issuer to allow the Holder to acquire or to require the Issuer
to repurchase such lesser number of shares as may be permissible, without any
amendment or modification hereof.

     18. All notices, requests, claims, demands and other communications
hereunder shall be deemed to have been duly given when delivered in Person, by
cable, telegram, telecopy or telex, or by registered or certified mail (postage
prepaid, return receipt requested) at the respective addresses of the parties
set forth in the Acquisition Agreement.

     19. This Agreement shall be governed by and construed in accordance with
the laws of the Commonwealth of Massachusetts, regardless of the laws that might
otherwise govern under applicable principles of conflicts of laws thereof.

     20. This Agreement may be executed in two or more counterparts, each of
which shall be deemed to be an original, but all of which shall constitute one
and the same agreement.

     21. Except as otherwise expressly provided herein, each of the parties
hereto shall bear and pay all costs and expenses incurred by it or on its behalf
in connection with the transactions contemplated hereunder, including fees and
expenses of its own financial consultants, investment bankers, accountants and
counsel.

     22. Except as otherwise expressly provided herein, this Agreement contains
the entire agreement between the parties with respect to the transactions
contemplated hereunder and supersedes all prior arrangements or understandings
with respect thereof, written or oral. The terms and conditions of this
Agreement shall inure to the benefit of and be binding upon the parties hereto
and their respective successors and permitted assigns. Nothing in this
Agreement, express or implied, is intended to confer upon any party, other than
the parties hereto, and their respective successors and permitted assigns, any
rights, remedies, obligations or liabilities under or by reason of this
Agreement, except as expressly provided herein.

     23. Capitalized terms used in this Agreement and not defined herein shall
have the meanings assigned thereto in the Acquisition Agreement.



                                      C-12

<PAGE>   170





        IN WITNESS WHEREOF, each of the parties has caused this Agreement to be
executed as a sealed instrument on its behalf by its officers thereunder duly
authorized, all as of the day and year first above written.

                                      WALDEN BANCORP, INC.

                                      By:    /s/  David E. Bradbury
                                             ----------------------------
                                             Name:     David E. Bradbury
                                             Title:    President

                                      UST CORP.

                                      By:    /s/  Neal F. Finnegan
                                             ----------------------------
                                             Name:     Neal F. Finnegan
                                             Title:    President




                                      C-13

<PAGE>   171

                                                                      APPENDIX D
                                                                      ----------

                          [FOX-PITT, KELTON LETTERHEAD]

November 5, 1996

Board of Directors
UST Corp.
40 Court Street
Boston, Massachusetts  02108

Ladies and Gentlemen:

Fox-Pitt, Kelton Inc. ("Fox-Pitt, Kelton") understands that UST Corp. ("UST")
and Walden Bancorp, Inc. ("Walden") have entered into an Affiliation Agreement
and Plan of Reorganization, dated as of August 30, 1996 (the "Merger
Agreement"), which provides, among other things, for the merger (the "Merger")
of Mosaic Corp., a newly formed wholly owned UST subsidiary (the "Merger
Subsidiary"), with and into Walden. Pursuant to the Merger Agreement and subject
to certain exceptions set forth therein, at the effective time of the Merger,
each issued and outstanding share of common stock of Walden, par value $1.00 per
share (the "Walden Common Stock"), shall be converted into the right to receive
1.9 shares (the "Exchange Ratio") of common stock of UST, par value $0.625 per
share (the "UST Common Stock"). The terms and conditions of the Merger are more
fully set forth in the Merger Agreement.

You have asked for Fox-Pitt, Kelton's opinion as to whether the Exchange Ratio
is fair, from a financial point of view, to UST.

In arriving at the opinion set forth below, Fox-Pitt, Kelton has, among other
things:

     (a)  reviewed and analyzed certain publicly available financial statements
          for UST and Walden;

     (b)  analyzed certain internal financial statements, including financial
          projections, and other financial and operating data prepared by the
          managements of UST and Walden;

     (c)  discussed the past, present and future operations, financial condition
          and prospects of UST and Walden with senior executives of the
          respective companies;

     (d)  reviewed the reported prices and trading activity of UST Common Stock
          and Walden Common Stock;

     (e)  compared the financial performance and condition of UST and Walden and
          the reported prices and trading activity of UST Common Stock and
          Walden Common Stock with that of certain other comparable publicly
          traded companies;

     (f)  reviewed and discussed with senior executives of UST and Walden the
          strategic objectives of the Merger and the synergies and certain other
          benefits of the Merger to UST;

<PAGE>   172


     (g)  reviewed the financial terms, to the extent publicly available, of
          certain merger and acquisition transactions comparable, in whole or in
          part, to the Merger;

     (h)  reviewed the Merger Agreement; and

     (i)  performed such other analyses as we have deemed appropriate.

Fox-Pitt, Kelton has assumed and relied upon, without independent verification,
the accuracy and completeness of all of the financial and other information it
has reviewed for the purposes of providing this opinion, and we have not assumed
any responsibility for independent verification of such information. Fox-Pitt,
Kelton has not assumed any responsibility for independent valuation of the
assets and liabilities of UST or Walden nor does it assume any responsibility
for reviewing loan files or visiting branch locations. With respect to the
financial projections, Fox-Pitt, Kelton has assumed that they have been
reasonably prepared by the respective managements of UST and Walden on bases
reflecting the best currently available estimates and judgments of the future
financial performance of UST and Walden, including projected cost savings and
operating synergies from the Merger. We express no view as to such projections
or the assumptions on which they are based. Fox-Pitt, Kelton's opinion is based
upon economic, market and other conditions as they exist and can be evaluated on
November 4, 1996.

In the normal course of its investment banking business, Fox-Pitt, Kelton is
regularly engaged in the valuation of banking and thrift company securities in
connection with acquisitions, negotiated underwritings, secondary distributions
of listed and unlisted securities, private placements and valuations for various
other purposes. As specialists in the securities of banking and thrift
companies, Fox-Pitt, Kelton has experience in, and knowledge of, the valuation
of such enterprises.

In the normal course of its business, Fox-Pitt, Kelton provides research
coverage on UST and has traded the equity securities of UST for its own account
and for the accounts of customers and, accordingly, may at any time hold a long
or short position in such securities. We have acted as financial advisor to UST
in connection with this Merger and have received a fee for our work performed to
date and we also will be receiving a fee upon the completion of the Merger.

It is understood that this letter is for the information of the Board of
Directors of UST and may not be used for any other purpose without our prior
written consent except for inclusion in a proxy statement related to the Merger,
which we have had an opportunity to review. This opinion does not constitute a
recommendation to any shareholder of UST as to how any such shareholder should
vote on the Merger.

Based upon and subject to the foregoing, Fox-Pitt, Kelton is of the opinion on
the date hereof that the Exchange Ratio is fair, from a financial point of view,
to UST.

Very truly yours,

/s/ FOX-PITT, KELTON INC.


FOX-PITT, KELTON INC.


                                      D-2

<PAGE>   173

                                                                      APPENDIX E
                                                                      ----------

                            [PAINEWEBBER LETTERHEAD]

November 5, 1996

Board of Directors
Walden Bancorp, Inc.
125 Nagog Park
Acton, MA  01720

Gentlemen:

     Walden Bancorp, Inc. (the "Company") and UST Corp. (the "Acquiring Company"
or the "Purchaser"), propose to enter into a transaction (the "Merger") in which
the Company will be acquired by the Purchaser and each share of the company's
common stock, par value $1.00 per share (the "Shares"), will be converted into
1.9 shares of the Acquiring Company's common stock (the "Consideration"), par
value $0.625 per share (the "Acquiring Company Shares"). The Merger is expected
to be considered by the shareholders of the Company and the Acquiring company at
special meetings and consummated shortly thereafter.

     You have asked us whether, in our opinion, the proposed Consideration to be
received by the shareholders of the company pursuant to the Merger is fair to
the shareholders of the Company from a financial point of view.

     In arriving at the opinion set forth below, we have, among other things:

     (1)  Reviewed the Company's audited Annual Reports, Forms 10-K, Forms F-2
          and related financial information for the five fiscal years ended
          December 31, 1995 and the Company's Form 10-Q and related unaudited
          financial information for the six months ended June 30, 1996;

     (2)  Reviewed certain unaudited financial information for the year ended
          December 31, 1995 and the nine months ended September 30, 1996, 
          relating to the Company;


     (3)  Reviewed the Acquiring Company's audited Annual Reports, Forms 10-K
          and related financial information for the five fiscal years ended
          December 31, 1995 and the Acquiring Company's Form 10-Q and related
          unaudited financial information for the six months ended June 30,
          1996;

     (4)  Reviewed certain unaudited financial information for the year ended
          December 31, 1995 and the nine months ended September 30, 1996, 
          relating to the Acquiring Company;

     (5)  Reviewed certain information, including financial forecasts, relating
          to the business, earnings, cash flow, assets and prospects of the
          Company, confidentially furnished to us by the Company;

     (6)  Reviewed certain information, including financial forecasts, relating
          to the business, earnings, cash flow, assets and prospects of the
          Acquiring company, confidentially furnished to us by the Acquiring
          Company;

     (7)  Conducted discussion with members of senior management of the Company
          concerning its businesses and prospects;


<PAGE>   174


     (8)  Conducted discussions with members of senior management of the
          Acquiring Company concerning its businesses and prospects;

     (9)  Reviewed the historical market prices and trading activity for the
          Shares and the Acquiring Company Shares and compared them with those
          of certain publicly traded companies which we deemed to be reasonably
          similar to the Company and the Acquiring Company, respectively;

     (10) Compared the results of operations of the Company and the Acquiring
          Company with those of certain companies which we deemed to be
          reasonably similar to the Company and the Acquiring Company,
          respectively;

     (11) Compared the proposed financial terms of the Merger with the financial
          terms of certain other mergers and acquisitions which we deemed to be
          relevant;

     (12) Reviewed the definitive agreement relating to the proposed
          Consideration to be received in the Merger; and

     (13) Reviewed such other financial studies and analyses and performed such
          other investigations and taken into account such other matters as we
          deemed necessary, including our assessment of general economic, market
          and monetary conditions.

     In preparing our opinion, we have relied on the accuracy and completeness
of all information supplied or otherwise made available to us by the Company and
the Acquiring Company and from generally recognized public sources, and we have
not assumed any responsibility to independently verify such information or
undertaken an independent appraisal of the assets of the Company or the
Acquiring Company. With respect to the financial forecasts examined by us, we
have assumed that they were reasonably prepared and reflect good faith estimates
and judgments of the management of the Company and the Acquiring Company
respectively as to future performance of the Company and the Acquiring Company.
We have not reviewed the loan files of either the Company or the Acquiring
Company. This opinion does not address the relative merits of the Merger or any
other transactions or business strategies considered by the Board of Directors
of the Company as alternatives to the Merger or the decisions of the Board of
Directors to proceed with the Merger. No opinion is expressed herein as to the
price at which the securities to be issued in the Merger to the shareholders of
the Company may trade at any time. Our opinion is based on economic, monetary
and market conditions existing on the date hereof.

     Our opinion is directed to the Board of Directors of the Company and does
not constitute a recommendation to any shareholder of the Company as to how any
such shareholder should vote on the Merger.

     On the basis of, and subject to the foregoing, we are of the opinion that
the proposed Consideration to be received by the shareholders of the Company
pursuant to the Merger is fair to such shareholders from a financial point of
view.

                                Very truly yours,


                                /s/ PAINEWEBBER INCORPORATED


                                PAINEWEBBER INCORPORATED


                                      E-2
<PAGE>   175

                           [ALTERNATE WALDEN PAGE]

                                                                      APPENDIX F
                                                                      ----------

                TEXT OF SECTIONS 85 TO 98 OF CHAPTER 156B OF THE
                     MASSACHUSETTS BUSINESS CORPORATION LAW

[Section]85.  DISSENTING STOCKHOLDER; RIGHT TO DEMAND PAYMENT FOR STOCK; 
EXCEPTION

     A stockholder in any corporation organized under the laws of Massachusetts
which shall have duly voted to consolidate or merge with another corporation or
corporations under the provisions of sections seventy-eight or seventy-nine who
objects to such consolidation or merger may demand payment for his stock from
the resulting or surviving corporation and an appraisal in accordance with the
provisions of sections eighty-six to ninety-eight, inclusive, and such
stockholder and the resulting or surviving corporation shall have the rights and
duties and follow the procedure set forth in those sections. This section shall
not apply to the holders of any shares of stock of a constituent corporation
surviving a merger if, as permitted by subsection (c) of section seventy-eight,
the merger did not require for its approval a vote of the stockholders of the
surviving corporation.

[Section]86.  SELECTIONS APPLICABLE TO APPRAISAL; PREREQUISITES

     If a corporation proposes to take a corporate action as to which any
section of this chapter provides that a stockholder who objects to such action
shall have the right to demand payment for his shares and an appraisal thereof,
sections eighty-seven to ninety-eight, inclusive, shall apply except as
otherwise specifically provided in any section of this chapter. Except as
provided in sections eighty-two and eighty-three, no stockholder shall have such
right unless (1) he files with the corporation before the taking of the vote of
the shareholders on such corporate action, written objection to the proposed
action stating that he intends to demand payment for his shares if the action is
taken and (2) his shares are not voted in favor of the proposed action.

[Section]87.  STATEMENT OF RIGHTS OF OBJECTING STOCKHOLDERS IN NOTICE OF 
MEETING; FORM

     The notice of the meeting of stockholders at which the approval of such
proposed action is to be considered shall contain a statement of the rights of
objecting stockholders. The giving of such notice shall not be deemed to create
any rights in any stockholder receiving the same to demand payment for his
stock, and the directors may authorize the inclusion in any such notice of a
statement of opinion by the management as to the existence or non-existence of
the right of the stockholders to demand payment for their stock on account of
the proposed corporate action. The notice may be in such form as the directors
or officers calling the meeting deem advisable, but the following form of notice
shall be sufficient to comply with this section:

               "If the action proposed is approved by the stockholders at the
          meeting and effected by the corporation, any stockholder (1) who files
          with the corporation before the taking of the vote on the approval of
          such action, written objection to the proposed action stating that he
          intends to demand payment for his shares if the action is taken and
          (2) whose shares are not voted in favor of such action has or may have
          the right to demand in writing from the corporation (or, in the case
          of a consolidation or merger, the name of the resulting or surviving
          corporation shall be inserted), within twenty days after the date of
          mailing to him of notice in writing that the corporate action has
          become effective, payment for his shares and an appraisal of the value
          thereof. Such corporation and any such stockholder shall in such cases
          have the rights and duties and shall follow the procedure set forth in
          sections 88 to 98, inclusive, of chapter 156B of the General Laws of
          Massachusetts."


<PAGE>   176
                           [ALTERNATE WALDEN PAGE]


[Section]88.    NOTICE OF EFFECTIVENESS OF ACTION OBJECTED TO

     The corporation taking such action, or in the case of a merger or
consolidation the surviving or resulting corporation, shall, within ten days
after the date on which such corporate action became effective, notify each
stockholder who filed a written objection meeting the requirements of section
eighty-six and whose shares were not voted in favor of the approval of such
action, that the action approved at the meeting of the corporation of which he
is a stockholder has become effective. The giving of such notice shall not be
deemed to create any rights in any stockholder receiving the same to demand
payment for his stock. The notice shall be sent by registered or certified mail,
addressed to the stockholder at his last known address as it appears in the
records of the corporation.

[Section]89.    DEMAND FOR PAYMENT; TIME FOR PAYMENT

     If within twenty days after the date of mailing of a notice under
subsection (e) of section eighty-two, subsection (f) of section eighty-three, or
section eighty-eight, any stockholder to whom the corporation was required to
give such notice shall demand in writing from the corporation taking such
action, or in the case of a consolidation or merger from the resulting or
surviving corporation, payment for his stock, the corporation upon which such
demand is made shall pay to him the fair value of his stock within thirty days
after the expiration of the period during which such demand may be made.

[Section]90.    DEMAND FOR DETERMINATION OF VALUE; BILL IN EQUITY; VENUE

     If during the period of thirty days provided for in section eighty-nine the
corporation upon which such demand is made and any such objecting stockholder
fail to agree as to the value of such stock, such corporation or any such
stockholder may within four months after the expiration of such thirty-day
period demand a determination of the value of the stock of all such objecting
stockholders by a bill in equity filed in the superior court in the county where
the corporation in which such objecting stockholder held stock had or has its
principal office in the commonwealth.

[Section]91.    PARTIES TO SUIT TO DETERMINE VALUE; SERVICE

     If the bill is filed by the corporation, it shall name as parties
respondent all stockholders who have demanded payment for their shares and with
whom the corporation has not reached agreement as to the value thereof. If the
bill is filed by a stockholder, he shall bring the bill in his own behalf and in
behalf of all other stockholders who have demanded payment for their shares and
with whom the corporation has not reached agreement as to the value thereof, and
service of the bill shall be made upon the corporation by subpoena with a copy
of the bill annexed. The corporation shall file with its answer a duly verified
list of all such other stockholders, and such stockholders shall thereupon be
deemed to have been added as parties to the bill. The corporation shall give
notice in such form and returnable on such date as the court shall order to each
stockholder party to the bill by registered or certified mail, addressed to the
last known address of such stockholder as shown in the records of the
corporation, and the court may order such additional notice by publication or
otherwise as it deems advisable. Each stockholder who makes demand as provided
in section eighty-nine shall be deemed to have consented to the provisions of
this section relating to notice, and the giving of notice by the corporation to
any such stockholder in compliance with the order of the court shall be a
sufficient service of process on him. Failure to give notice to any stockholder
making demand shall not invalidate the proceedings as to other stockholders to
whom notice was properly given, and the court may at any time before the entry
of a final decree make supplementary orders of notice.



                                      F-2


<PAGE>   177
                           [ALTERNATE WALDEN PAGE]

[Section]92.    DECREE DETERMINING VALUE AND ORDERING PAYMENT; VALUATION DATE

     After hearing the court shall enter a decree determining the fair value of
the stock of those stockholders who have become entitled to the valuation of and
payment for their shares, and shall order the corporation to make payment of
such value, together with interest, if any, as hereinafter provided, to the
stockholders entitled thereto upon the transfer by them to the corporation of
the certificates representing such stock if certificated or, if uncertificated,
upon receipt of an instruction transferring such stock to the corporation. For
this purpose, the value of the shares shall be determined as of the day
preceding the date of the vote approving the proposed corporate action and shall
be exclusive of any element of value arising from the expectation or
accomplishment of the proposed corporate action.

[Section]93.    REFERENCE TO SPECIAL MASTER

     The court in its discretion may refer the bill or any question arising
thereunder to a special master to hear the parties, make findings and report the
same to the court, all in accordance with the usual practice in suits in equity
in the superior court.

[Section]94.    NOTATION ON STOCK CERTIFICATES OF PENDENCY OF BILL

     On motion the court may order stockholder parties to the bill to submit
their certificates of stock to the corporation for the notation thereon of the
pendency of the bill and may order the corporation to note such pendency in its
records with respect to any uncertificated shares held by such stockholder
parties, and may on motion dismiss the bill as to any stockholder who fails to
comply with such order.

[Section]95.    COSTS; INTEREST

     The costs of the bill, including the reasonable compensation and expenses
of any master appointed by the court, but exclusive of fees of counsel or of
experts retained by any party, shall be determined by the court and taxed upon
the parties to the bill, or any of them, in such manner as appears to be
equitable, except that all costs of giving notice to stockholders as provided in
this chapter shall be paid by the corporation. Interest shall be paid upon any
award from the date of the vote approving the proposed corporate action, and the
court may on application of any interested party determine the amount of
interest to be paid in the case of any stockholder.

[Section]96.    DIVIDENDS AND VOTING RIGHTS AFTER DEMAND FOR PAYMENT

     Any stockholder who has demanded payment for his stock as provided in this
chapter shall not thereafter be entitled to notice of any meeting of
stockholders or to vote such stock for any purpose and shall not be entitled to
the payment of dividends or other distribution on the stock (except dividends or
other distributions payable to stockholders of record at a date which is prior
to the date of the vote approving the proposed corporate action) unless:

     (1) A bill shall not be filed within the time provided in section ninety;
     (2) A bill, if filed, shall be dismissed as to such stockholder; or
     (3) Such stockholder shall with the written approval of the corporation, or
     in the case of a consolidation or merger, the resulting or surviving
     corporation, deliver to it a written withdrawal of his objections to and an
     acceptance of such corporate action.

     Notwithstanding the provisions of clauses (1) to (3), inclusive, said
stockholder shall have only the rights of a stockholder who did not so demand
payment for his stock as provided in this chapter.

                                      F-3
<PAGE>   178
                           [ALTERNATE WALDEN PAGE]


[Section]97.    STATUS OF SHARES PAID FOR

     The shares of the corporation paid for by the corporation pursuant to the
provisions of this chapter shall have the status of treasury stock, or in the
case of a consolidation or merger the shares or the securities of the resulting
or surviving corporation into which the shares of such objecting stockholder
would have been converted had he not objected to such consolidation or merger
shall have the status of treasury stock or securities.

[Section]98.    EXCLUSIVE REMEDY; EXCEPTION

     The enforcement by a stockholder of his right to receive payment for his
shares in the manner provided in this chapter shall be an exclusive remedy
except that this chapter shall not exclude the right of such stockholder to
bring or maintain an appropriate proceeding to obtain relief on the ground that
such corporate action will be or is illegal or fraudulent as to him.

                                   F-4
<PAGE>   179
 
                                    PART II
 
                   INFORMATION NOT REQUIRED IN THE PROSPECTUS
 
ITEM 20.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.
 
     Section 67 of Chapter 156B of the Massachusetts General Laws authorizes a
corporation to indemnify any director, officer, employee or other agent of the
corporation to whatever extent specified in or authorized by (a) the articles of
organization, (b) a by-law adopted by the stockholders or (c) a vote adopted by
the holders of a majority of the shares of stock entitled to vote on the
election of directors.
 
     The Registrant's Articles of Organization provide that the Registrant
shall, to the fullest extent legally permissible, indemnify each person who is
or was a director, officer, employee or other agent of the Registrant and each
person who is or was serving at the request of the Registrant as such of another
corporation or of any partnership, joint venture, trust, employee benefit plan
or other enterprise or organization, against all liabilities, costs and
expenses, including but not limited to amounts paid in satisfaction of
judgments, in settlement or as fines and penalties, and counsel fees and
disbursements, reasonably incurred by him or her in connection with the defense
or disposition of or otherwise in connection with or resulting from any action,
suit or other proceeding, whether civil, criminal, administrative or
investigative, before any court or administrative or legislative or
investigative body, in which he or she may be or may have been involved as a
party or otherwise or with which he or she may be or may have been threatened,
while in office or thereafter, by reason of his or her being or having been such
a director, officer, employee, agent or trustee, or by reason of any action
taken or not taken in any such capacity. Under Massachusetts law and the
Articles, no indemnification may be provided for any person with respect to any
matter as to which he or she shall have been adjudicated in any proceeding not
to have acted in good faith in the reasonable belief that his or her action was
in the best interest of the Registrant or other entity served or, to the extent
that such matter relates to service with respect to an employee benefit plan, in
the best interest of the participants or beneficiaries of such employee benefit
plan.
 
     If, in an action, suit or proceeding brought by or in the name of the
Registrant, a director of the Registrant is held not liable for monetary
damages, whether because that director is relieved of personal liability under
the provisions of the Articles of Organization, or otherwise, that director
shall be deemed to have met the standard of conduct set forth above and to be
entitled to indemnification for expenses reasonably incurred in the defense of
such action, suit or proceeding.
 
     As to any matter disposed of by settlement pursuant to a consent decree or
otherwise, no indemnification either for the amount of such settlement or for
any other expenses shall be provided unless such settlement shall be approved as
in the best interests of the Registrant, after notice that it involves such
indemnification, (a) by vote of a majority of the disinterested directors then
in office (even though the disinterested directors be less than a quorum), (b)
by any disinterested person or persons to whom the question may be referred by
vote of a majority of such disinterested directors, or (c) by vote of the
holders of a majority of the outstanding stock at the time entitled to vote for
directors, voting as a single class, exclusive of any stock owned by any
interested person, or (d) by any disinterested person or persons to whom the
question may be referred by vote of the holders or a majority of such stock. No
such approval shall prevent the recovery from any such officer, director,
employee, agent or trustee of any amounts paid to him or her or on his or her
behalf as indemnification in accordance with the preceding sentence if such
person is subsequently adjudicated by a court of competent jurisdiction not to
have acted in good faith in the reasonable belief that his or her action was in
the best interests of the Registrant.
 
     The right of indemnification provided in the Registrant's Articles of
Organization shall not be exclusive of or affect any other rights to which any
director, officer, employee, agent or trustee may be entitled or which may
lawfully be granted to him or her. Indemnification of a "director", "officer",
"employee", "agent", and "trustee" includes their respective executors,
administrators and other legal representatives. An "interested" person is one
against whom the action, suit or other proceeding in question or another action,
suit or other proceeding on the same or similar grounds is then or had been
pending or threatened, and a "disinterested" person is a person against whom no
such action, suit or other proceeding is then or had been pending or threatened.
 
                                      II-1
<PAGE>   180
 
ITEM 21. EXHIBITS AND FINANCIAL STATEMENTS.
 
     (a)  The following is a list of exhibits to this Registration Statement:
 
<TABLE>
      <C>         <C>     <S>
         (2)(a)     --    Affiliation Agreement and Plan of Reorganization, dated as of August
                          30, 1996, by and between UST and Walden (included as Appendix A to
                          the Proxy Statement -- Prospectus).
         (2)(b)     --    Agreement and Plan of Merger, dated as of August 30, 1996, by and
                          among UST, Walden and Merger Subsidiary (included as Appendix B to
                          the Proxy Statement -- Prospectus).
         (2)(c)     --    Stock Option Agreement, dated as of August 30, 1996, by and between
                          UST and Walden (included as Appendix C to the Proxy Statement --
                          Prospectus).
         (3)(a)     --    Articles of Organization of UST, as amended to date, incorporated
                          herein by reference to Exhibit 3(a) to UST's Annual Report on Form
                          10-K for the year ended December 31, 1994.
         (3)(b)     --    By-Laws of UST, as amended to date, incorporated herein by reference
                          to
                          Exhibit 3(b) to UST's Annual Report on Form 10-K for the year ended
                          December 31, 1994.
         (4)        --    Rights Agreement, dated as of September 19, 1995, between UST and
                          United States Trust Company, as Rights Agent, and the description of
                          the Rights, incorporated herein by reference to UST's Registration
                          Statement on Form 8-A relating to the Rights and to Exhibit 1 of such
                          Registration Statement.
         (5)        --    Opinion of Eric R. Fischer, Esq.
         (8)(a)     --    Form of Opinion of Bingham, Dana & Gould LLP as to certain tax
                          matters.
         (8)(b)     --    Opinion of Arthur Andersen LLP as to certain tax matters.
         (23)(a)    --    Consent of Arthur Andersen LLP (concerning UST financials).
         (23)(b)    --    Consent of Arthur Andersen LLP (concerning Walden and Braintree
                          financials).
         (23)(c)    --    Consent of KPMG Peat Marwick LLP.
         (23)(d)    --    Consent of Eric R. Fischer, Esq. (included in Exhibit 5).
         (23)(e)    --    Consent of Bingham, Dana & Gould LLP.
         (23)(f)    --    Consent of Fox-Pitt, Kelton Inc.
         (23)(g)    --    Consent of PaineWebber, Incorporated.
         (23)(h)    --    Consent of David E. Bradbury.
         (24)       --    Power of Attorney of certain officers and directors (included on
                          pages II-5 - II-8).
         (99)(a)    --    Form of Proxy for Special Meeting of Stockholders of UST.
         (99)(b)    --    Form of Proxy for Special Meeting of Stockholders of Walden.
         (99)(c)    --    Text of Sections 85 to 98 of the Massachusetts Business Corporations
                          Law (included as Appendix F to the Joint Proxy Statement --
                          Prospectus).
</TABLE>
 
     (b)  Financial Statements Schedules:
 
           Not Applicable.
 
     (c)  Fairness Opinions:
 
       Included in Part I as Appendices D and E to the Joint Proxy Statement --
       Prospectus included in this Registration Statement.
 
ITEM 22. UNDERTAKINGS.
 
     The undersigned registrant hereby undertakes:
 
     (1) To file, during any period in which offers or sales are being made, a
post-effective amendment to this registration statement;
 
                                      II-2
<PAGE>   181
 
     (i) To include any prospectus required by Section 10(a)(3) of the
Securities Act of 1933;
 
     (ii) To reflect in the prospectus any facts or events arising after the
effective date of the registration statement (or the most recent post-effective
amendment thereof) which, individually or in the aggregate, represent a
fundamental change in the information set forth in the registration statement.
Notwithstanding the foregoing, any increase or decrease in volume of securities
offered (if the total dollar value of securities offered would not exceed that
which was registered) and any deviation from the low or high and of the
estimated maximum offering rate may be reflected in the form of prospectus filed
with the Commission pursuant to Rule 424(b) if, in the aggregate, the changes in
volume and price represent not more than 20 percent change in the maximum
aggregate offering price set forth in the "Calculation of Registration Fee"
table in the effective registration statement.
 
     (iii) To include any material information with respect to the plan of
distribution not previously disclosed in the registration statement or nay
material change to such information in the registration statement;
 
     (2) That, for the purpose of determining any liability under the Securities
Act of 1933, each such post-effective amendment shall be deemed to be a new
registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.
 
     (3) To remove from registration by means of a post-effective amendment any
of the securities being registered which remain unsold at the termination of the
offering.
 
     The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Exchange Act that is incorporated by reference in the Registration Statement
shall be deemed to be a new registration statement relating to the securities
offered therein, and the offering of such securities at that time shall be
deemed to be the initial bona fide offering thereof.
 
     The undersigned Registrant hereby undertakes as follows: that prior to any
public reoffering of the securities registered hereunder through use of a
prospectus which is a part of this Registration Statement, by any person or
party who is deemed to be an underwriter within the meaning of Rule 145(c), the
Registrant undertakes that such reoffering prospectus will contain the
information called for by the applicable registration form with respect to
reofferings by persons who may be deemed underwriters, in addition to the
information called for by the other Items of the applicable form.
 
     The Registrant undertakes that every prospectus (i) that is filed pursuant
to the immediately preceding paragraph, or (ii) that purports to meet the
requirements of Section 10(a)(3) of the Securities Act and is used in connection
with an offering of securities subject to Rule 415, will be filed as a part of
an amendment to the Registration Statement and will not be used until such
amendment is effective, and that, for the purposes of determining any liability
under the Securities Act, each such post-effective amendment shall be deemed to
be a new registration statement relating to the securities offered therein, and
the offering of such securities at that time shall be deemed to be the initial
bona fide offering thereof.
 
     Insofar as indemnification for liabilities arising under the Securities Act
may be permitted to directors, officers and controlling persons of the
Registrant pursuant to the foregoing provisions, or otherwise, the Registrant
has been advised that in the opinion of the Commission such indemnification is
against public policy as expressed in the Securities Act and is, therefore,
unenforceable. In the event that a claim for indemnification against such
liabilities (other that the payment by the Registrant of expenses incurred or
paid by a director, officer or controlling person of the Registrant in the
successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the Registrant will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Securities Act and will be governed by the final
adjudication of such issue.
 
                                      II-3
<PAGE>   182
 
     The undersigned Registrant hereby undertakes to respond to requests for
information that is incorporated by reference into the Joint Proxy Statement
- -Prospectus pursuant to Item 4, 10(b), 11 or 13 of this Form S-4, within one
business day of receipt of such request, and to send the incorporated documents
by first class mail or other equally prompt means. This includes information
contained in documents filed subsequent to the effective date of the
Registration Statement through the date of responding to the request.
 
     The undersigned Registrant hereby undertakes to supply by means of a
post-effective amendment all information concerning a transaction, and the
company being acquired involved therein, that was not the subject of and
included in the Registration Statement when it became effective.
 
                                      II-4
<PAGE>   183
 
                                   SIGNATURES
 
     Pursuant to the requirements of the Securities Act of 1933, the Registrant
has duly caused this S-4 Registration Statement to be signed on its behalf by
the undersigned, thereunto duly authorized, in the City of Boston, and The
Commonwealth of Massachusetts, on the 5th day of November, 1996.
 
                                            UST Corp.
 
                                               /S/ ERIC R. FISCHER
                                            By .................................
 
                                               Eric R. Fischer
                                               (Executive Vice President,
                                               General Counsel and Clerk)
 
     Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the dates indicated. By so signing, each of the undersigned,
in his or her capacity as a director or officer, or both, as the case may be, of
the Registrant, does hereby appoint Neal F. Finnegan, James K. Hunt and Eric R.
Fischer, and each of them severally, or if more than one acts, a majority of
them, his or her true and lawful attorneys or attorney to execute in his or her
name, place and stead, in his or her capacity as a director or officer or both,
as the case may be, of the Registrant, the Registration Statement on Form S-4
and with respect to the shares of UST Common Stock issued in connection with
UST's proposed acquisition of Walden and any and all amendments to said
Registration Statement and all instruments necessary or incidental in connection
therewith, and to file the same with the Securities and Exchange Commission.
Each of said attorneys shall have full power and authority to do and perform in
the name and on behalf of each of the undersigned, in any and all capacities,
every act whatsoever requisite or necessary to be done in the premises as fully
and to all intents and purposes as each of the undersigned might or could do in
person, hereby ratifying and approving the acts of said attorneys and each of
them.
 
<TABLE>
<CAPTION>
                SIGNATURE                               TITLE                       DATE
- ------------------------------------------  ------------------------------    -----------------
<S>                                         <C>                               <C>
/S/ NEAL F. FINNEGAN                        President and Chief Executive      November 5, 1996
 ........................................    Officer (Principal Executive
(Neal F. Finnegan)                          Officer) and Director

/S/ JAMES K. HUNT                           Executive Vice President and       November 5, 1996
 ........................................    Treasurer (Principal Financial
(James K. Hunt)                             Officer and Principal
                                            Accounting Officer)

/S/ ROBERT M. COARD                         Director                           November 5, 1996
 ........................................
(Robert M. Coard)

/S/ DOMENIC COLASACCO                       Director                           November 5, 1996
 ........................................
(Domenic Colasacco)

/S/ ROBERT L. CULVER                        Director                           November 5, 1996
 ........................................
(Robert L. Culver)

/S/ ALAN K. DERKAZARIAN                     Director                           November 5, 1996
 ........................................
(Alan K. DerKazarian)
</TABLE>
 
                                      II-5
<PAGE>   184
 
<TABLE>
<CAPTION>
                SIGNATURE                               TITLE                       DATE
- ------------------------------------------  ------------------------------    -----------------
<S>                                         <C>                               <C>
/S/ DONALD C. DOLBEN                        Director                           November 5, 1996
 ........................................
(Donald C. Dolben)

/S/ EDWARD GUZOVKSY                         Director                           November 5, 1996
 ........................................
(Edward Guzovsky)

/S/ WALLACE M. HASELTON                     Director                           November 5, 1996
 ........................................
(Wallace M. Haselton)

/S/ BRIAN W. HOTAREK                        Director                           November 5, 1996
 ........................................
(Brian W. Hotarek)
                                            Director                           November  , 1996
 ........................................
(Francis X. Messina)

/S/ SYDNEY L. MILLER                        Director                           November 5, 1996
 ........................................
(Sydney L. Miller)

/S/ VIKKI L. PRYOR                          Director                           November 5, 1996
 ........................................
(Vikki L. Pryor)

/S/ GERALD M. RIDGE                         Director                           November 5, 1996
 ........................................
(Gerald M. Ridge)

/S/ WILLIAM SCHWARTZ                        Director                           November 5, 1996
 ........................................
(William Schwartz)
                                            Director                           November  , 1996
 ........................................
(Barbara C. Sidell)
                                            Director                           November  , 1996
 ........................................
(James V. Sidell)
                                            Director                           November  , 1996
 ........................................
(Paul D. Slater)

/S/ EDWARD J. SULLIVAN                      Director                           November 5, 1996
 ........................................
(Edward J. Sullivan)

/S/ MICHAEL J. VERROCHI, JR.                Director                           November 5, 1996
 ........................................
(Michael J. Verrochi, Jr.)

/S/ GORDON M. WEINER                        Director                           November 5, 1996
 ........................................
(Gordon M. Weiner)
</TABLE>
 
                                      II-6

<PAGE>   1
                                                                       EXHIBIT 5
                                November 5, 1996
UST Corp.
40 Court Street
Boston, Massachusetts 02108

     Re: UST CORP. REGISTRATION STATEMENT ON FORM S-4
         --------------------------------------------
         RELATING TO 10,611,549 SHARES OF COMMON STOCK
         ---------------------------------------------

Ladies and Gentlemen:

     This opinion is rendered to you in connection with the filing by UST Corp.,
a Massachusetts corporation, (the "Corporation") of its Registration Statement
on Form S-4 (the "Registration Statement") with the Securities and Exchange
Commission, relating to the registration under the Securities Act of 1933 of
10,611,549 shares of the Corporation's Common Stock, par value $0.625 per share
(the "Common Stock") to be issued in connection with an Affiliation Agreement
and Plan of Reorganization between the Corporation and Walden Bancorp, Inc.
("Walden") and the related Agreement and Plan of Merger (collectively, the
"Merger Agreement") among the Corporation, Mosaic Corp., a wholly-owned
subsidiary of the Corporation ("Mosaic") and Walden. Pursuant to the terms of
the Merger Agreement, Mosaic will be merged with and into Walden and Walden will
become a wholly-owned subsidiary of the Corporation. The Common Stock will be
issued by the Corporation to persons who were stockholders of Walden immediately
prior to the merger of Mosaic into Walden.

     In rendering this opinion as General Counsel of the Corporation, I and
attorneys in my office acting under my direction have participated with the
Corporation and its officers in the preparation, review and filing of the
Registration Statement and the related joint proxy statement and prospectus (the
"Joint Proxy Statement - Prospectus"), have examined other corporate documents 
and records, have made such examination of law, and have discussed with the 
officers and directors of the Corporation and its subsidiaries such questions 
of fact as we have deemed necessary or appropriate. We have also relied upon 
certificates and statements of such officers and directors as to factual 
matters and have assumed the genuineness of all signatures not known to us as 
well as the authenticity of all documents submitted to us as copies.

     Subject to the foregoing and to the proposed additional proceedings being
taken as now contemplated prior to the issuance of the Common Stock, it is my
opinion that the Common Stock has been duly authorized and, upon the issuance
thereof in accordance with the terms of the Merger Agreement, will be validly
issued, fully paid and non-assessable, subject to the provisions of Section 45
of Chapter 156B of the Massachusetts General Laws.

     I hereby consent to the filing of this opinion as an Exhibit to the
Registration Statement and to the use of my name in the Registration Statement
and the related Joint Proxy Statement - Prospectus.


<PAGE>   2

                                                 Very truly yours,
                                                 /s/ Eric R. Fischer
                                                 Eric R. Fischer,
                                                 Executive Secretary,
                                                 General Counsel and Clerk

<PAGE>   1
                                                                    Exhibit 8(a)

                [Bingham, Dana & Gould LLP Form of Tax Opinion]

UST Corp.
40 Corn Street
Boston, Massachusetts 02108

Ladies and Gentlemen:

     This opinion is furnished to you pursuit to Section 6.02(d) of the
Affiliation Agreement and Plan of Reorganization dated as of August 30, 1996
(the "Affiliation Agreement"), between UST Corp., a Massachusetts corporation
("UST"), and Walden Bancorp, Inc., a Massachusetts corporation ("Walden").
Pursuit to the Affiliation Agreement and the related Agreement and Plan of
Merger dated as of August 30, 1996 (the "Plan of Merger"), among UST, Walden and
Mosaic Corp., a Massachusetts corporation ("Sub"), Sub, a newly incorporated
direct wholly-owned subsidiary of UST, will merge with and into Walden in a
transaction (the "Affiliation") in which the existing stockholders of Walden
will receive Common Stock, par value $0.625 per shoe, of UST ("UST Common
Stock") in exchange for their issued and outstanding shares of Common Stock, par
value $1.00 per shoe, of Walden ("Walden Common Stock"). You have requested our
opinion as to certain federal income tax consequences anticipated to follow from
implementation of the Affiliation Agreement and the Plan of Merger.

     For purposes of our opinion, we have examined and relied upon the originals
or copies, certified or otherwise identified to us to our satisfaction, of the
Affiliation Agreement, the Plan of Merger, the Joint Proxy Statement-Prospectus
dated November __, 1996 included in the Registration Statement on Form S-4 filed
by UST with the Securities and Exchange Commission in connection with the
Affiliation (Registration No. 333-____ ), and related documents (collectively,
the "Documents"). In that examination, we have assumed the genuineness of all
signatures, the authenticity and completeness of all documents purporting to be
originals (whether reviewed by us in original or copy form) and the conformity
to the originals of all documents purporting to be copies.

     As to certain factual matters, we have relied with your consent upon, and
our opinion is limited by, the representations of the various parties set forth
in the Documents and in the certificates from UST, Walden and Sub dated the date
hereof copies of which are attached hereto (the "Certificates"). Our opinion
assumes that all representations set forth in the Documents and in the
Certificates are true and correct in all material aspects as of the date hereof.
In addition, our opinion is limited solely to the provisions of the federal
Internal Revenue Code as now in effect (the "Code"), and the regulations,
rulings, and interpretations thereof in force as of this date and we assume no
obligation to advise you of changes in the law or fact that occur after the date
of this opinion.

     On the basis of and subject to the foregoing, and assuming due adoption and
implementation of the Affiliation Agreement and the Plan of Merger in accordance
with their respective terms (including satisfaction of all covenants and
conditions to the obligations of the parties without amendment or waiver
thereof) and consistent with the representations set out in the Documents and
Certificates, we are of the opinion that for federal income tax purposes, the
Affiliation will constitute a reorganization under Section 368 of the Code.


<PAGE>   2


Bank of Boston Corporation
_______________,1996
Page 2

     This opinion is being delivered solely to you for your use in connection
with the referenced transaction and for such other uses to which we have given
our prior written consent. It may not be relied upon by any other person or used
for any other purpose.

                            Very truly yours,



                            BINGHAM, DANA & GOULD LLP


<PAGE>   1
November 5, 1996



Mr. Michael O. Gilles
Executive Vice President, CFO & Treasurer
Walden Bancorp, Inc.
125 Nagog Park
Acton,  MA 01720

RE:  Acquisition of Walden Bancorp Inc. by UST Corp.



Dear Gentlemen:

         You have requested our opinion ("Tax Opinion") regarding certain
federal income tax consequences of the proposed merger ("Merger") of Mosaic
Corp. ("Mosaic"), a newly formed, wholly owned subsidiary of UST Corp. ("UST"),
with and into Walden Bancorp, Inc. ("Walden") with Walden surviving the Merger,
as more fully described below.

                              Scope of Tax Opinion

         In rendering our opinion, we have relied on the facts described below,
the information contained in the documents listed on Exhibit A of this Tax
Opinion, the Agreement of Affiliation and Plan of Reorganization dated August
30, 1996 (the "Plan"), and the Representation Letters signed by officers of
Walden and UST and dated November 5, 1996. You have represented to us that we
have been provided with all of the facts related to the subject transaction;
however, we have not independently audited or otherwise verified any of these
facts.

         Our opinion is expressed only with respect to certain federal income
tax consequences of the Merger that we consider to be material. Our opinion is
based on the Internal Revenue Code of 1986, as amended ("the Code"), the
regulations thereunder, reported judicial decisions, and the current position of
the Internal Revenue Service ("the Service") in such matters as reflected in
published and private rulings, procedures and announcements. However, federal
income tax laws and their interpretations are subject to change, which could
adversely affect this opinion. The opinion does not address any non-tax issues
such as state corporations laws and securities law, or any state or foreign
income tax issues. The opinion will not address the tax consequences particular
to special types of taxpayers, including, but not limited to, non-U.S.
shareholders and regulated investment companies.

         Our opinion reflects what we regard to be the federal income tax
effects of the Merger as described herein; nevertheless, it is an opinion only
and should not be taken as an assurance of ultimate tax treatment. Moreover, we
express no opinion on the federal income tax consequences of any other event
occurring pursuant to the Plan. The Service, of course, is not bound by this
opinion; however, should the Service challenge the tax treatment of the Merger,
we believe the tax treatment set forth in our opinion would prevail.
<PAGE>   2
Walden Bancorp, Inc.
Page 2
November 5, 1996



         If there is a change in the Code, the regulations and published rulings
thereunder, the current administrative rulings, or the prevailing judicial
interpretation of the foregoing, the opinion expressed herein would necessarily
have to be re-evaluated in light of any such changes. We have no responsibility
to update this opinion for events, transactions or circumstances occurring after
this date.

                              Proposed Transaction

         UST and Walden entered into the Plan on August 30, 1996. UST is a
registered bank holding company that owns a number of banking subsidiaries.
These subsidiaries provide financial services to individuals and small- to
medium-sized companies. Walden is a registered bank holding company that owns
all of the stock of The Co-operative Bank of Concord and The Bank of Braintree,
respectively. Pursuant to the Plan, Walden will become a wholly owned subsidiary
of UST.

         It is represented that UST wishes to acquire Walden so as to further
expand its share of the Boston area banking market. The Co-operative Bank of
Concord and The Bank of Braintree both operate in areas in which UST wishes to
expand its presence. By acquiring Walden, UST will have the opportunity to
expand into these markets. Moreover, UST believes that the acquisition will
benefit its employees, its shareholders, and the communities it serves due to
the enhanced strength and diversity of the combined company.

         Prior to the formation of Walden, The Co-operative Bank of Concord had
pursued a strategy of growth and expansion through acquisitions. In pursuit of
this strategy, Walden was formed in 1995 and, as part of such formation,
acquired The Bank of Braintree in a tax-free reorganization under section
368(a)(1)(A) and (a)(2)(D).(1) Through the proposed business combination, Walden
will become a part of a larger and more diverse banking operation and will be
afforded the opportunity to expand its market share.

         Pursuant to the Plan, the transaction will take place on or after
         January 10, 1997, as follows:

         1.       UST will form a wholly owned subsidiary under Massachusetts
                  law (Mosaic).

         2.       Mosaic will merge with and into Walden in a transaction
                  qualifying as a statutory merger under Massachusetts law, with
                  Walden surviving the Merger.

         3.       Pursuant to the Merger and by operation of Massachusetts law,
                  each share of Walden common stock held by a Walden shareholder
                  will be converted solely into the right to receive 1.9 shares
                  of UST voting common -- i.e., the Walden shareholders will
                  exchange their stock in Walden for voting common stock of UST.
                  In addition, as with the current

- --------
(1) All section references are to the Internal Revenue Code of 1986, as amended,
and underlying regulations.
<PAGE>   3
Walden Bancorp, Inc.
Page 3
November 5, 1996




                  UST shareholders, the Walden shareholders will receive the
                  right to purchase preferred shares of UST upon the occurrence
                  of certain events such as a hostile takeover attempt.

         4.       Each share of Mosaic held by UST will be converted to one
                  share of Walden common stock as a result of the Merger; thus,
                  Walden will become a wholly owned subsidiary of UST.

         5.       UST will assume no liabilities of Walden or acquire any Walden
                  assets from Walden.


       Tax Opinion Regarding Federal Income Tax Consequences of the Merger

         In our opinion, the Merger will constitute a tax-free reorganization as
defined in sections 368(a)(1)(A) and 368(a)(2)(E). Thus, UST, Mosaic, and Walden
will each be a party to the reorganization. Section 368(b).

         As a consequence of the Merger qualifying as a tax free reorganization,
it follows that:

         1.       No gain or loss will be recognized by the stockholders of
                  Walden upon the exchange of their Common Stock of Walden
                  solely for UST Common Stock. Section 354(a); Rev. Rul. 
                  90-11.(2)

         2.       The tax basis of the shares of UST Common Stock received in
                  the Merger by the Walden stockholders will be the same as the
                  tax basis of the Walden Common Stock surrendered in the
                  exchange. Section 358(a).

         3.       The holding period of the shares of UST Common Stock received
                  in the Merger by the Walden stockholders will include the
                  period during which the shares of
                  Walden common stock surrendered in exchange were held by the
                  Walden shareholders, provided that such shares of Walden stock
                  were held as capital assets. Section 1223(1).

         4.       No gain or loss will be recognized by Walden as a result of
                  the Merger. Sections 1032 and 361(c).

         5.       Stockholders of Walden who exercise their dissenters'
                  appraisal rights and receive cash in exchange for their shares
                  of the Common Stock of the Bank will recognize taxable income
                  or gain or loss for federal income tax purposes in connection
                  with the transaction. The amount of that income or gain or
                  loss and the character of that income or gain or loss (that
                  is, whether it constitutes ordinary income, short-term capital
                  gain or loss or long-term capital gain or loss) will turn upon
                  a number of factual considerations


- --------
(2) Rev. Rul. 90-11, 1990-1 C.B. 10
<PAGE>   4
Walden Bancorp, Inc.
Page 4
November 5, 1996





                  peculiar to the individual stockholder. Therefore, dissenting
                  shareholders are strongly encouraged to consult their tax
                  advisor in connection with this transaction.

         6.       A Walden shareholder receiving cash in lieu of fractional
                  share interests of UST stock in the exchange will be treated
                  as if he, she, or it actually received such fractional share
                  interests which were subsequently redeemed by UST. Therefore,
                  the cash the UST shareholders receive will be treated as
                  having been received as full payment in exchange for stock
                  redeemed as provided in section 302(a) of the Code. Rev. Rul.
                  66-365 and Rev. Proc. 77- 41.(3)


         Our opinions expressed above address only those federal income tax
aspects relating to the Merger that, in our judgment are material to Walden and
its stockholders. No opinion is expressed about the tax treatment of the Merger
under any other provisions of the Code and the Regulations or about the tax
treatment of any conditions existing at the time of, or effects resulting from,
the Merger that are not specifically covered by the above opinion. These
opinions are solely for your benefit and your shareholders and are not intended
to be relied upon by anyone other than you and your shareholders. Any other
party receiving a copy of this letter must consult and rely upon the advice of
his/her/its own counsel, accountant, or other advisor.

         We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement of UST Corp. on Form S-4 and to the references to this
Firm in the Registration Statement and the related Joint Proxy Statement
Prospectus.

                           
                               /s/ Arthur Andersen LLP

                               ARTHUR ANDERSEN LLP




- --------
(3) Rev. Rul. 66-365, 1966-2 C.B. 116; Rev. Proc. 77-41, 1977-2 C.B. 574
<PAGE>   5
                                    EXHIBIT A



- -        Agreement of Affiliation and Plan of Reorganization dated August 30,
         1996.


- -        Representation letters dated November 5, 1996.

<PAGE>   1
 
                                                                   EXHIBIT 23(A)
 
                       CONSENT OF INDEPENDENT PUBLIC ACCOUNTANTS
 
     As independent public accountants, we hereby consent to the incorporation
by reference in this registration statement on Form S-4 of our report dated
January 29, 1996, included in UST Corp's Form 10-K for the year ended December
31, 1995 and to all references to our Firm included in this registration
statement.
 
                                            /S/ ARTHUR ANDERSEN LLP
                                            -----------------------
                                            ARTHUR ANDERSEN LLP
 
Boston, Massachusetts
October 30, 1996

<PAGE>   1
 
                                                                   EXHIBIT 23(B)
 
                   CONSENT OF INDEPENDENT PUBLIC ACCOUNTANTS
 
     As independent public accountants, we hereby consent to the incorporation
by reference in this registration statement on Form S-4 of our report dated
January 25, 1996, included in Walden Bancorp, Inc.'s Form 10-K for the year
ended December 31, 1995 and to all references to our firm in this registration
statement.
 
                                            /S/ ARTHUR ANDERSEN LLP
                                            -----------------------
                                            ARTHUR ANDERSEN LLP
 
Boston, Massachusetts
October 30, 1996

<PAGE>   1
 
                                                                   EXHIBIT 23(C)
 
                        CONSENT OF INDEPENDENT AUDITORS
 
The Board of Directors
Walden Bancorp, Inc.:
 
     We consent to use of our report dated January 23, 1996 incorporated herein
by reference, relating to the December 31, 1994 consolidated financial
statements of The Co-operative Bank of Concord and subsidiaries and the
reference to our firm under the heading "Experts" in the prospectus which is a
part of the Registration Statement on Form S-4 for UST Corp.
 
                                            /S/ KPMG PEAT MARWICK LLP
                                            -------------------------
                                            KPMG PEAT MARWICK LLP
 
Boston, Massachusetts
October 30, 1996

<PAGE>   1
 
                                                                   EXHIBIT 23(E)
 
                      CONSENT OF BINGHAM, DANA & GOULD LLP
 
UST Corp.
40 Court Street
Boston, Massachusetts 02108
 
Ladies and Gentlemen:
 
     We hereby consent to the references to this Firm under the captions "THE
AFFILIATION -- Certain Federal Income Tax Consequences" and "Legal Opinions" in
the Joint Proxy Statement - Prospectus included in the Registration Statement on
Form S-4 to be filed with the Securities and Exchange Commission on November 5,
1996 by UST Corp. in connection with the proposed merger of your subsidiary
Mosaic Corp. with and into Walden Bancorp, Inc.
 
                                            Very truly yours,
 
                                            /S/ BINGHAM, DANA & GOULD LLP
                                            -----------------------------
                                            BINGHAM, DANA & GOULD LLP
 
November 5, 1996

<PAGE>   1
 
                                                                   EXHIBIT 23(F)
 
                        CONSENT OF FOX-PITT, KELTON INC.
 
UST Corp.
40 Court Street
Boston, Massachusetts 02108
 
Ladies and Gentlemen:
 
     We hereby consent to the use of our written opinion letter dated as of the
date of this Joint Proxy Statement - Prospectus to the Board of Directors of UST
Corp. included as Appendix D to the Joint Proxy Statement - Prospectus which
forms a part of the Registration Statement on Form S-4 relating to the proposed
merger of a wholly-owned subsidiary of UST Corp. with and into Walden Bancorp,
Inc. and to the references to such opinion, to our August 29, 1996 oral and
written opinion provided to the Board of Directors of UST Corp. and to this firm
in the Joint Proxy Statement - Prospectus. In giving such consent, we do not
admit that we come within the category of persons whose consent is required
under Section 7 of the Securities Act of 1933, as amended, or the rules and
regulations of the Securities and Exchange Commission thereunder, nor do we
admit that we are experts with respect to any part of such Registration
Statement within the meaning of the term "experts" as used in the Securities Act
of 1933, as amended, or the rules and regulations of the Securities and Exchange
Commission thereunder.
 
                                            FOX-PITT, KELTON INC.
 
                                            By: /s/  PETER E. ROTH
                                              ----------------------------------
                                              Name: Peter E. Roth
                                              Title:   Managing Director
 
November 5, 1996

<PAGE>   1
 
                                                                   EXHIBIT 23(G)
 
                      CONSENT OF PAINEWEBBER INCORPORATED
 
Walden Bancorp, Inc.
125 Nagog Park
Acton, Massachusetts 01720
 
Ladies and Gentlemen:
 
     We hereby consent to the use of our written opinion letter dated as of the
date of this Joint Proxy Statement - Prospectus to the Board of Directors of
Walden Bancorp, Inc. included as Appendix E to the Joint Proxy Statement -
Prospectus which forms part of the Registration Statement on Form S-4 relating
to the proposed merger of a wholly-owned subsidiary of UST Corp. with and into
Walden Bancorp, Inc. and to the references to such opinion, to our August 29,
1996 oral and written opinion and to this firm in such Joint Proxy Statement -
Prospectus. In giving such consent, we do not admit that we come within the
category of persons whose consent is required under Section 7 of the Securities
Act of 1933, as amended, or the rules and regulations of the Securities and
Exchange Commission thereunder, nor do we admit that we are experts with respect
to any part of such Registration Statement within the meaning of the term
"experts" as used in the Securities Act of 1933, as amended, or the rules and
regulations of the Securities and Exchange Commission thereunder.
 
                                            Very truly yours,
 
                                            PAINEWEBBER INCORPORATED
 
                                            By: /s/  JAMES W. KILMAN, JR.
 
                                              ----------------------------------
                                              Name: James W. Kilman, Jr.
                                              Title:   Managing Director
 
November 5, 1996

<PAGE>   1
 
                                                                   EXHIBIT 23(H)
 
                          CONSENT OF DIRECTOR DESIGNEE
 
     The undersigned hereby consents, pursuant to Rule 438 under the Securities
Act of 1933, to the references to him in the SUMMARY and under the caption "THE
AFFILIATION -- Management and Operations After the Affiliation" in the Joint
Proxy Statement - Prospectus included in this Registration Statement.
 
                                            /S/ DAVID E. BRADBURY
                                            ....................................
 
                                            David E. Bradbury
 
Acton, Massachusetts
November 1, 1996

<PAGE>   1
                                                                  Exhibit 99(a)


                                     [Front]

                                    UST CORP.
         THIS PROXY IS SOLICITED BY THE BOARD OF DIRECTORS OF UST CORP.

The undersigned stockholder of UST Corp., a Massachusetts corporation (the
"Company"), hereby constitutes and appoints Neal F. Finnegan, Eric R. Fischer
and James K. Hunt, and each of them, his Attorneys and Proxies (with full power
of substitution in each), and hereby authorizes them to represent the
undersigned and to vote, as designated on the reverse, all the shares of Common
Stock of the Company held of record by the undersigned on November 4, 1996 at
the Special Meeting of Stockholders of the Company, to be held on Tuesday,
December 17, 1996, and at any adjournments thereof.

THE PROXY WHEN PROPERLY EXECUTED WILL BE VOTED IN THE MANNER DIRECTED HEREIN BY
THE UNDERSIGNED HOLDER, IF NO DIRECTION IS MADE, THIS PROXY WILL BE VOTED FOR
PROPOSALS 1 AND 2.

- --------------------------------------------------------------------------------
   PLEASE VOTE AND SIGN ON OTHER SIDE AND RETURN PROMPTLY IN ENCLOSED ENVELOPE
- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------

Please sign this Proxy exactly as your name appears on the books of the Company.
Joint owners should each sign personally. Trustee and other fiduciaries should
indicate the capacity in which they sign, and where more than one name appears,
a majority must sign. If a corporation, this signature should be that of the
authorized officer who should state his or her title.

- --------------------------------------------------------------------------------


HAS YOUR ADDRESS CHANGED?                    DO YOU HAVE ANY COMMENTS?

- ----------------------------------           -----------------------------------

- ----------------------------------           -----------------------------------

- ----------------------------------           -----------------------------------






<TABLE>
<S>                                                              <C> 
/X/   PLEASE MARK VOTE
      AS IN THIS EXAMPLE


1.) Aproval of the Affiliation Agreement with                      2.) Amendment to UST Articles increasing the 
Walden Bancorp, Inc., including the Plan of Merger               number of authorized shares.                 
and the transactions contemplated thereby.             
                                                                                For     Against     Abstain
                                                                                / /       / /         / /
          For     Against     Abstain 
          / /       / /         / /   
                                                                   Authorizing the Proxies in their discretion to  
                                                                   consider and act upon such other matters as may 
                                                                   properly come before the meeting.               




                                                  ------------
Please be sure to sign and date Date this proxy.  Date

- --------------------------------------------------------------

Shareholder sign here    Co-owner sign here
- --------------------------------------------------------------
                                                                   Mark box at right if comments or address   / /
                                                                   change have been noted on the reserve   
                                                                   side of the card.                       
</TABLE>


<PAGE>   1

                                                                 Exhibit 99(b)



<TABLE>
                                                           REVOCABLE PROXY
                                                        WALDEN BANCORP, INC.

<S>                                                                       <C>
/X/   PLEASE MARK VOTES
      AS IN THIS EXAMPLE

                   SPECIAL MEETING OF STOCKHOLDERS
                          DECEMBER 17, 1996                               1.     Approval of the Affiliation Agreement, including
          THIS PROXY IS SOLICITED BY THE BOARD OF DIRECTORS               the Plan of Merger with UST Corp. dated as of August 30,
                                                                          1996, and the transactions contemplated thereby.
         The undersigned hereby appoints David E. Bradbury, Josiah                                  For     Against     Abstain
S. Cushing, II and each of them with full powers of substitution, to                                / /       / /         / /
act as attorneys and proxies for the undersigned to vote all shares                                       
of Common Stock of Walden Bancorp, Inc. ("Walden") which the         
undersigned is entitled to vote at the Special Meeting of Stockholders,
to be held at the Westford Regency Inn and Conference Center on Tuesday,
December 17, 1996 at 11:00 a.m., and any and all adjournments thereto.

                                                                          THIS PROXY WILL BE VOTED AS DIRECTED, BUT IF NO          
                                                                          DIRECTIONS ARE SPECIFIED, THIS PROXY WILL BE VOTED FOR   
                                                                          THE PROPOSITION STATED. IF ANY OTHER BUSINESS IS         
                                                                          PRESENTED AT SUCH MEETING, THIS PROXY WILL BE VOTED BY   
                                                                          THE PERSONS NAMED IN THIS PROXY IN THEIR DISCRETION. AT  
                                                                          THE PRESENT TIME, THE BOARD OF DIRECTORS KNOWS OF NO     
                                                                          OTHER BUSINESS TO BE PRESENTED AT THE MEETING. THIS PROXY
                                                                          ALSO CONFERS DISCRETIONARY AUTHORITY ON THE PROXY HOLDERS
                                                                          TO VOTE WITH RESPECT TO APPROVAL OF THE MINUTES OF THE   
                                                                          PRIOR MEETING OF STOCKHOLDERS, AND MATTERS INCIDENT TO   
                                                                          THE CONDUCT OF THE MEETING.

                                                    --------------------   Should the undersigned be present and elect to vote all  
Please be sure to sign and date                      Date                 the Meeting or any adjournment thereof and after          
  this Proxy in the box                                                   notification to the Clerk of Walden at the Meeting of the 
- ------------------------------------------------------------------------  stockholder's decision to terminate this proxy, then the  
                                                                          power of said attorneys and proxies shall be deemed       
                                                                          terminated and of no further force and effect.            
Stockholder sign above        Co-holder (if any) sign above     
                                                                           THE BOARD OF DIRECTORS RECOMMENDS A VOTE "FOR" THE 
                                                                          LISTED PROPOSITION.  
- ------------------------------------------------------------------------  
- ------------------------------------------------------------------------------------------------------------------------------------
                              Detach above card, sign, date and mail in postage paid envelope provided

                                                        WALDEN BANCORP, INC.

- ------------------------------------------------------------------------------------------------------------------------------------
         The above singed acknowledges receipt from Walden prior to the execution of this proxy of a notice of the Meeting and a
Joint Proxy Statement-Prospectus dated November 5, 1996.

         Please sign exactly as your name appears on this proxy card. When signing as attorney, executor, administrator, trustee, or
guardian, please give your full title. If shares are held jointly, each holder should sign.

                                                         PLEASE ACT PROMPTLY
                                               SIGN, DATE & MAIL YOUR PROXY CARD TODAY
- ------------------------------------------------------------------------------------------------------------------------------------
</TABLE>




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