Exhibit 24.2

                                POWER OF ATTORNEY

I, Mark Byrne, being a director of White Mountains Insurance Group, Ltd. hereby
appoint and constitute K. Thomas Kemp and Gordon S. Macklin, and each of them
singly, my true and lawful attorneys with full power to them, and each of them
singly, to sign for me and in my name any and all amendments (including
post-effective amendments) to this registration statement (or to any other
registration statement for the same offering that is to be effective upon filing
pursuant to Rule 462(b) under the Securities Act), and generally to do all such
things in my name and in my capacity as a director to enable White Mountains
Insurance Group, Ltd. to comply with the provisions of the Securities Act of
1933 and all requirements of the Securities and Exchange Commission, hereby
ratifying and confirming my signature as it may be signed by my said attorneys,
or any of them, to said registration statement and any and all amendments
thereto.

         Pursuant to the requirements of the Securities Act of 1933, this
registration statement has been signed by me as a director of White Mountains
Insurance Group, Ltd. on the date indicated:




Dated this 7th Day of December, 2001.


SIGNED   /s/ Mark Byrne
         ----------------------------
         Name: Mark Byrne