FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

    Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

OMB Number: 3235-0287
Expires: January 31, 2005
Estimated average burden
hours per response. . .0.5

Filed By Romeo & Dye's Instant Form 4 Filer
www.section16.net

1. Name and Address of Reporting Person*

Byrne John Joseph

2. Issuer Name and Ticker or Trading Symbol
White Mountains Insurance Group, Ltd. (WTM)

6. Relationship of Reporting Person(s)
to Issuer (Check all applicable)
X Director                                   X 10% Owner
X Officer (give title below)          Other (specify below)

Chairman and Chief Executive Officer              

(Last)      (First)     (Middle)

c/o White Mountains Insurance Group, Ltd.
28 Gates Street

3. I.R.S. Identification Number
of Reporting Person,
if an entity (voluntary)

(Street)

White River Junction, VT 05001

(City)     (State)     (Zip)

Table I — Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned

1. Title of Security
(Instr. 3)

2. Trans-
action
Date
(Month/ Day/
Year)

2A. Deemed
Execution
Date,
if any
(Month/Day/
Year)

3. Trans-
action Code
(Instr. 8)

4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 & 5)

5. Amount of
Securities
Beneficially
Owned Follow-
ing Reported Transactions(s)
(Instr. 3 & 4)

6. Owner-
ship Form:
Direct (D)
or Indirect (I)
(Instr. 4)

7. Nature of Indirect
Beneficial Ownership
(Instr. 4)

Code

V

Amount

(A)
or
(D)

Price

Common Shares

12/24/02

12/24/02

G

V

6,270⁽¹⁾

D

$319

762,922

D

Common Shares

380,909⁽²⁾

I

by Trust

Common Shares (restricted)

25,000

D

Common Shares

2⁽³⁾

I

401K

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security

(Instr. 3)

2. Conver-
sion or
Exercise
Price of Derivative Security

3. Trans-
action Date

(Month/
Day/
Year)

4. Trans-
action
Code

(Instr. 8)

5. Number of Derivative Securities Acquired (A) or Disposed of (D)

(Instr. 3, 4 & 5)

6. Date Exercisable
and Expiration
Date
(Month/Day/
Year)

7. Title and Amount of Underlying Securities
(Instr. 3 & 4)

8. Price of Derivative Security
(Instr. 5)

9. Number of
Derivative
Securities
Beneficially
Owned
Following
Reported Transaction(s)
(Instr. 4)

10. Owner-
ship Form
of Deriv-
ative
Security:
Direct (D)
or Indirect (I)
(Instr. 4)

11. Nature of Indirect Beneficial Ownership
(Instr. 4)

Code

V

(A)

(D)

Date Exer-cisable

Expira-
tion
Date

Title

Amount or Number of
Shares

Explanation of Responses:

(1) Gifts to family trusts.
(2) Represents shares held in a Grantor Retained Annuity Trust (the Jack Byrne 2001 Grat No.1) dated May 15, 2001 (the "Trust"). The Reporting Person originally contributed a total of 650,000 shares into the Trust on May 15, 2001. At December 31, 2002, 380,909 shares remain in the Trust following a 2002 mandatory distribution. The remaining shares in the Trust continue to be beneficially owned by Mr. Byrne indirectly.
(3) During the year ended December 31, 2002, the Reporting Person acquired 2 shares of WTM's Common Shares under the OneBeacon Insurance Group 401(k) plan. The information in this report is based on a plan statement dated as of December 31, 2002

**Intentional misstatements or omissions of facts constitute Federal Criminal Violations.
See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

Note: File three copies of this Form, one of which must be manually signed.
          If space is insufficient, See Instruction 6 for procedure.

Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.