<PAGE>
NOTICE OF GUARANTEED DELIVERY
FOR
TENDER OF SHARES OF COMMON STOCK
OF
UNITED ASSET MANAGEMENT CORPORATION
TO
OM ACQUISITION CORP.
A WHOLLY-OWNED SUBSIDIARY
OF
OLD MUTUAL PLC
(NOT TO BE USED FOR SIGNATURE GUARANTEES)
THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT,
NEW YORK
CITY TIME, ON FRIDAY, AUGUST 11, 2000, UNLESS THE OFFER IS
EXTENDED.
This Notice of Guaranteed Delivery, or a form substantially equivalent to
it, must be used to accept the Offer (as defined below) if certificates
representing shares of common stock, par value $0.01 per share (the 'Shares'),
of United Asset Management Corporation, a Delaware corporation, are not
immediately available, if the procedure for book-entry transfer cannot be
completed prior to the Expiration Date (as defined in Section 1 of the Offer to
Purchase), or if time will not permit all required documents to reach the
Depositary prior to the Expiration Date. This form may be delivered by hand,
transmitted by facsimile transmission or mailed to the Depositary. See Section 3
of the Offer to Purchase.
THE DEPOSITARY FOR THE OFFER IS:
CHASEMELLON SHAREHOLDER SERVICES, L.L.C.
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By Mail: By Hand: Overnight:
ChaseMellon Shareholder ChaseMellon Shareholder ChaseMellon Shareholder
Services, L.L.C. Services, L.L.C. Services, L.L.C.
P.O. Box 3301 120 Broadway, 13th Floor 85 Challenger Road
South Hackensack, NJ 07606 New York, NY 10271 Ridgefield Park, NJ 07660
Attn: Reorg. Dept. Attn: Reorg. Dept. Attn: Reorg. Dept.
By Facsimile Transmission
(for Eligible Institutions only):
(201) 296-4293
Confirm by Telephone:
(201) 296-4860
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DELIVERY OF THIS NOTICE OF GUARANTEED DELIVERY TO AN ADDRESS OTHER THAN AS
SPECIFIED ABOVE OR TRANSMISSION OF INSTRUCTIONS VIA FACSIMILE TO A NUMBER OTHER
THAN AS SPECIFIED ABOVE WILL NOT CONSTITUTE A VALID DELIVERY.
This form is not to be used to guarantee signatures. If a signature on a
Letter of Transmittal is required to be guaranteed by an 'Eligible Institution'
under the instructions to such Letter of Transmittal, such signature guarantee
must appear in the applicable space provided in the signature box on the Letter
of Transmittal.
The Eligible Institution that completes this form must communicate the
guarantee to the Depositary and must deliver the Letter of Transmittal and
certificates for Shares to the Depositary within the time period shown herein.
Failure to do so could result in a financial loss to such Eligible Institution.
THE GUARANTEE ON THE REVERSE SIDE MUST BE COMPLETED.
<PAGE>
Ladies and Gentlemen:
The undersigned hereby tenders to OM Acquisition Corp., a Delaware
corporation ('Purchaser') and a wholly-owned subsidiary of Old Mutual plc, a
public limited company incorporated in England and Wales ('Parent'), upon the
terms and subject to the conditions contained in Purchaser's Offer to Purchase,
dated July 17, 2000 (the 'Offer to Purchase'), and the related Letter of
Transmittal (which, together with any amendments and supplements thereto,
constitute the 'Offer'), receipt of which is hereby acknowledged, the number of
shares indicated below of common stock, par value $0.01 per share (the
'Shares'), of United Asset Management Corporation, a Delaware corporation (the
'Company'), pursuant to the guaranteed delivery procedures described in Section
3 of the Offer to Purchase.
Number of Shares:...........................................................
Certificate Nos. (if available):
............................................................................
............................................................................
Check box if Shares will be tendered by book-entry transfer: [ ]
Account Number: ...........................................................
Dated:................................................................, 2000
Name(s) of Record Holder(s): ..............................................
............................................................................
............................................................................
PLEASE PRINT
Address(es):................................................................
............................................................................
............................................................................
ZIP CODE
Area Code and Tel. No.:
............................................................................
............................................................................
Signature(s): .............................................................
............................................................................
GUARANTEE
(NOT TO BE USED FOR SIGNATURE GUARANTEES)
The undersigned, a participant in the Security Transfer Agents Medallion
Program, the New York Stock Exchange Medallion Signature Guarantee Program
or the Stock Exchange Medallion Program, guarantees to deliver to the
Depositary either certificates representing the Shares tendered hereby, in
proper form for transfer, or confirmation of book-entry transfer of such
Shares into the Depositary's account at The Depository Trust Company, in
each case with delivery of a properly completed and duly executed Letter of
Transmittal (or facsimile thereof), with any required signature guarantees,
or an Agent's Message, and any other documents required by the Letter of
Transmittal, within three New York Stock Exchange trading days after the
date hereof.
The Eligible Institution that completes this form must communicate the
guarantee to the Depositary and must deliver the Letter of Transmittal and
certificates for Shares to the Depositary within the same time period stated
herein. Failure to do so could result in a financial loss to such Eligible
Institution.
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Name of Firm: ............................... ..............................................
AUTHORIZED SIGNATURE
Address: .................................... Name: .......................................
PLEASE PRINT
............................................. Title: ......................................
ZIP CODE
Area Code & Tel. No: ........................ Date:..................................., 2000
</TABLE>
DO NOT SEND CERTIFICATES FOR SHARES WITH THIS NOTICE. CERTIFICATES
SHOULD BE SENT ONLY WITH YOUR LETTER OF TRANSMITTAL.
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