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                                                                     EXHIBIT 8.1

                                BAKER & MCKENZIE
                                805 THIRD AVENUE
                              NEW YORK, N.Y. 10022

                                                               September 7, 1999

Trenwick Group, Inc.
One Canterbury Green
Stamford, Connecticut 06901

Ladies and Gentlemen:

     We have acted as counsel to Trenwick Group Inc., a Delaware corporation
(the "Company"), in connection with the merger of Chartwell Re Corporation, a
Delaware corporation ("Chartwell"), with and into the Company, pursuant to the
Agreement and Plan of Merger, dated as of June 21, 1999, by and between
Chartwell and the Company (the "Agreement"). We render this opinion to you, in
part, in connection with the registration of the Trenwick Common Stock to be
issued in connection with the Merger. All capitalized terms used and not
otherwise defined herein shall have the meanings provided in the Agreement.

     For purposes of this opinion, we have reviewed the Agreement and such other
documents and matters of law and fact as we have considered necessary or
appropriate and have relied, with the consent of the Company and the consent of
Chartwell, upon the accuracy and completeness of the statements and
representations contained, respectfully, in the representation letters of the
Company and Chartwell to us and LeBoeuf, Lamb, Greene & MacRae, L.L.P., counsel
to Chartwell, and have assumed the same will be true, complete and accurate as
of the Effective Time. We have assumed the genuineness of all signatures, the
legal capacity of all natural persons, the authenticity of all documents
submitted to us as originals, the conformity to original documents of all
documents submitted to us as certified, conformed or photostatic copies and the
authenticity of the original of such copies. We have also relied upon the
accuracy of the Joint Proxy Statement/Prospectus of the Company and Chartwell
(the "Joint Proxy Statement/Prospectus"). We have further assumed that (i) the
transactions contemplated by the Agreement will be consummated in accordance
therewith and as described in the Joint Proxy Statement/Prospectus, and (ii) the
Merger will qualify as a statutory merger under the laws of the State of
Delaware.

     Based upon and subject to the foregoing it is our opinion, under currently
applicable United States federal income tax law, that:

          (1) The Merger will constitute a reorganization within the meaning of
     Section 368(a) of the Internal Revenue Code of 1986, as amended (the
     "Code");

          (2) Each of the Company and Chartwell will be a party to that
     reorganization within the meaning of Section 368(b) of the Code; and

          (3) No gain or loss will be recognized by the stockholders of
     Chartwell who exchange all of their Chartwell Common Stock solely for
     shares of Trenwick Common Stock pursuant to the Merger (except with respect
     to cash received in lieu of a fractional share interest in Trenwick Common
     Stock).

     We express no opinion as to the United States federal income tax
consequences of the merger to stockholders subject to special treatment under
United States federal income tax law, such as foreign persons, dealers in
securities, traders in securities that elect to use a mark-to-market method of
accounting, tax-exempt organizations, stockholders who acquired shares of
Chartwell Common Stock through the exercise of options, grants of performance
shares under Chartwell's equity based compensation plans or otherwise as
compensation, or through a tax-qualified retirement plan, or holders that hold
Chartwell Common Stock as part of a straddle or conversion transaction. In
addition, no opinion is expressed with
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respect to the tax consequences of the Merger under applicable foreign, state or
local laws or under any federal tax laws other than those pertaining to income
tax.

     We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the references to us under the heading "Important
Federal Income Tax Consequences of the Merger" in the Joint Proxy
Statement/Prospectus. In giving such consent we do not thereby admit that we are
in the category of persons whose consent is required under Section 7 of the
Securities Act of 1933, as amended.

                                          Very truly yours,

                                          /s/ BAKER & MCKENZIE
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                                               Baker & McKenzie