SC TO-I/A

================================================================================
     As filed with the Securities and Exchange Commission on June 13, 2002
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                   ----------

                                   SCHEDULE TO
             Tender Offer Statement under Section 14(d)(1) or 13(e)
                     Of the Securities Exchange Act of 1934
                                (AMENDMENT NO. 3)

                                   ----------

                               TRENWICK GROUP LTD.
                       (Name of Subject Company -- Issuer)

                               TRENWICK GROUP LTD.
                       (Name of Filing Person -- Offeror)

                                   ----------

          OPTIONS TO PURCHASE COMMON SHARES, PAR VALUE $.10 PER SHARE,
  ISSUED UNDER THE TRENWICK GROUP INC. 1989 STOCK PLAN, THE TRENWICK GROUP INC.
     1993 STOCK OPTION PLAN, THE CHARTWELL RE CORPORATION 1993 STOCK OPTION
    PLAN, THE CHARTWELL RE CORPORATION 1997 OMNIBUS STOCK INCENTIVE PLAN AND
         THE LASALLE RE HOLDINGS LIMITED 1996 LONG-TERM INCENTIVE PLAN
                         (Title of Class of Securities)

                                   ----------

                                 JOHN V. DEL COL
                                    SECRETARY
                               TRENWICK GROUP LTD.
                              CONTINENTAL BUILDING
                                25 CHURCH STREET
                             HAMILTON HM 12, BERMUDA
                             TELEPHONE: 441-292-4985
                             FACSIMILE: 441-292-2656
       (Name, address and telephone number of person authorized to receive
             notices and communications on behalf of Filing Person)

                                   ----------

                                   A COPY TO:
                                JAMES R. CAMERON
                                BAKER & MCKENZIE
                                 805 THIRD AVE.
                            NEW YORK, NEW YORK 10022
                             TELEPHONE: 212-891-3930
                             FACSIMILE: 212-891-3835



Check the appropriate boxes below to designate any transactions to which the
statement relates:

|_|  third-party tender offer subject to Rule 14d-1.
|X|  issuer tender offer subject to Rule 13e-4.
|_|  going-private transaction subject to Rule 13e-3.
|_|  amendment to Schedule 13D under Rule 13d-2.

Check the following box if the filing is a final amendment reporting the results
of the tender offer: |_|

      This Amendment No. 3 amends and supplements the Tender Offer Statement on
Schedule TO, dated May 16, 2002, and amended by Amendment No. 1 and Amendment
No. 2 (the "Tender Offer Statement") filed by Trenwick Group Ltd., a Bermuda
corporation ("Trenwick"), relating to the offer by Trenwick to exchange
outstanding employee options to purchase its common shares granted under the
Trenwick Group Inc. 1989 Stock Plan, the Trenwick Group Inc. 1993 Stock Option
Plan, the Chartwell Re Corporation 1993 Stock Option Plan, the Chartwell Re
Corporation 1997 Omnibus Stock Incentive Plan and the LaSalle Re Holdings
Limited 1996 Long-Term Incentive Plan for new options to purchase its common
shares, upon the terms and subject to the conditions set forth in the Offer to
Exchange, which was attached to the Tender Offer Statement, as Exhibit 99.2, as
amended.

ITEM 12. Exhibits.

      Item 12 of the Tender Offer Statement is hereby amended to add a reference
to Exhibit 99.10, which is attached hereto, as follows:

            99.10 Form of Reminder Email to Eligible Employees - June 12, 2002



                                    SIGNATURE

      After due inquiry and to the best of my knowledge and belief, I certify
that the information set forth in this Amendment No. 3 to Schedule TO is true,
complete and correct.

Dated: June 13, 2002

                                        TRENWICK GROUP LTD.


                                              By: /s/ John V. Del Col
                                                  ------------------------------
                                                  Name:  John V. Del Col
                                                  Title: Secretary

EX-99.10

                                                                   Exhibit 99.10

Date:       June 12, 2002

To:         Eligible Employees of Trenwick Group Ltd.

Subject:    Last Week to Elect to Participate in the Stock Option Exchange
            Program

If you wish to participate in the Stock Option Exchange Program, this Friday is
the deadline for making or changing your election. If you do not make an
election prior to 11:59 p.m. Eastern Time (U.S.) on June 14, 2002, you will not
be allowed to participate in the Stock Option Exchange Program.

Due to the short amount of time remaining, if you want to participate in the
Stock Option Exchange Program or change your election, we strongly recommend
that you send your election form to us via fax (Fax No. 203-353-5550). If you
mail your election or change form this week, there is no guarantee that your
form will be received by June 14th. Remember, your participation or change is
determined by the date we receive your election or change, not the postmark
date.

Election or change forms received after June 14th will NOT be accepted.

If you do NOT want to participate in the Stock Option Exchange Program, you do
not need to make an election. No response from you will mean that your current
options remain in effect under the original terms and conditions of those
options.

If you have any questions, please feel free to call me. My telephone number is
(203) 602-3074.