<PAGE>




                       Securities and Exchange Commission

                              Washington, DC 20549

                  Under the Securities and Exchange Act of 1934
                                  Schedule 13G


                               Trenwick Group Ltd.
                                (Name of Issuer)

                          Common Stock, Par Value $.10
                         (Title of Class of Securities)

                                    G9032C109
                                 (CUSIP Number)


<PAGE>




1)         Name of Reporting Person:        CNA Financial Corporation

           SS or IRS Identification         36-6169860
           Nos. of Above Persons:

2)         Check the Appropriate Box        (a)       (b) X
           If A Member of Group
           (See Instructions)

3)         SEC Use Only

4)         Citizenship or Place of Organization      Delaware

           Number of             (5)  Sole Voting Power         0
           Shares
           Beneficially Owned    (6)  Shared Voting Power       3,707,400
           by Each Reporting
           Person With:          (7)  Sole Dispositive Power    0

                                 (8)  Shared Dispositive Power: 3,707,400

9)         Aggregate Amount Beneficially
           Owned by Each Reporting Person                       3,707,400

10)        Check if the Aggregate Amount in Row (9)
           Excludes Certain Shares (See Instructions)

11)        Percent of Class
           Represented By Amount in Row 9                       10.1%

12)        Type of Reporting
           Person (See Instructions)                            HC

Under Illinois Law, assets owned by Continental  Casualty  Company,  an Illinois
insurance company, are solely under the control of the board of directors of the
insurer.  The  characterization  of shared  dispositive  power  with the  parent
holding company is made solely as a consequence of SEC interpretations regarding
control of the  subsidiary.  CNA  Financial  Corporation  and Loews  Corporation
specifically disclaim beneficial ownership of the securities identified herein.


<PAGE>




1)         Name of Reporting Person:        Loews Corporation

           SS or IRS Identification         13-2646102
           Nos. of Above Persons:

2)         Check the Appropriate Box        (a)       (b) X
           If A Member of Group
           (See Instructions)

3)         SEC Use Only

4)         Citizenship or Place of Organization      Delaware

           Number of             (5)  Sole Voting Power         0
           Shares
           Beneficially Owned    (6)  Shared Voting Power       3,707,400
           by Each Reporting
           Person With:          (7)  Sole Dispositive Power    0

                                 (8)  Shared Dispositive Power: 3,707,400

9)         Aggregate Amount Beneficially
           Owned by Each Reporting Person                       3,707,400

10)        Check if the Aggregate Amount in Row (9)
           Excludes Certain Shares (See Instructions)

11)        Percent of Class
           Represented By Amount in Row 9                       10.1%

12)        Type of Reporting
           Person (See Instructions)                            HC

Under  Illinois Law,  assets owned by Continental  Casualty  Company an Illinois
insurance company, are solely under the control of the board of directors of the
insurer.  The  characterization  of shared  dispositive  power  with the  parent
holding company is made solely as a consequence of SEC interpretations regarding
control of the  subsidiary.  CNA  Financial  Corporation  and Loews  Corporation
specifically disclaim beneficial ownership of the securities identified herein.


<PAGE>




1)         Name of Reporting Person:        Continental Casualty Company

           SS or IRS Identification         36-2114545
           Nos. of Above Persons:

2)         Check the Appropriate Box     (a)       (b) X
           If A Member of Group
           (See Instructions)

3)         SEC Use Only

4)         Citizenship or Place of Organization      Illinois

           Number of             (5)  Sole Voting               0
           Shares
           Beneficially Owned    (6)  Shared Voting             3,707,400
           by Each Reporting
           Person With:          (7)  Sole Dispositive Power    0

                                 (8)  Shared Dispositive Power: 3,707,400

9)         Aggregate Amount Beneficially
           Owned by Each Reporting Person                       3,707,400

10)        Check if the Aggregate Amount in Row (9)
           Excludes Certain Shares (See Instructions)

11)        Percent of Class
           Represented By Amount in Row 9                       10.1%

12)        Type of Reporting
           Person (See Instructions)                            IC

Under  Illinois Law,  assets owned by Continental  Casualty  Company an Illinois
insurance company, are solely under the control of the board of directors of the
insurer.  The  characterization  of shared  dispositive  power  with the  parent
holding company is made solely as a consequence of SEC interpretations regarding
control of the  subsidiary.  CNA  Financial  Corporation  and Loews  Corporation
specifically disclaim beneficial ownership of the securities identified herein.


<PAGE>




Item 1(a).  Name of Issuer.

     The name of the issuer is Trenwick Group Ltd.(the "Company").

Item 1(b).  Address of Issuer's Principal Executive Offices.

The principal executive offices of the Issuer are located at:

                                             Continental Building
                                             25 Church Street
                                             Hamilton HM12, Bermuda.

Item 2(a). Name of Persons Filing:          CNA Financial Corporation
                                            Loews Corporation
                                            Continental Casualty Company

Item 2(b). Address of Principal Business Office:

           Continental Casualty Company - CNA Plaza, Chicago, Illinois 60685 CNA
           Financial  Corporation  - CNA Plaza,  Chicago,  Illinois  60685 Loews
           Corporation - 667 Madison Avenue, New York, New York 10021-8087


Item 2(c). Citizenship:

           Continental Casualty Company - State of Illinois
           CNA Financial Corporation - State of Delaware
           Loews Corporation - State of Delaware


Item 2(d). Title of Class of Securities:

                                            Common Stock

Item 2(e). CUSIP Number:                    G9032C109

Item       3. The persons  filing  this  statement  pursuant to Rule  13-1(b) or
           13d-2 are each:

(g) Parent  Holding  Company (HC) (Relevant  subsidiary is Continental  Casualty
Company, an Illinois domiciled insurance company.) or an Insurance Company (IC).


<PAGE>




Item 4.    Ownership.

Under  Illinois Law,  assets owned by Continental  Casualty  Company an Illinois
insurance company, are solely under the control of the board of directors of the
insurer.  The  characterization  of shared  dispositive  power  with the  parent
holding company is made solely as a consequence of SEC interpretations regarding
control.)

                                     Continental    CNA          Loews
                                     Casualty       Financial    Corporation
                                     Company        Corp.

(a)   Amount Beneficially Owned:     3,707,400       3,707,400    3,707,400

(b)   Percent of Class               10.1%           10.1%        10.1%




Item 4.

                                     Continental    CNA          Loews
                                     Casualty       Financial    Corporation
                                     Company        Corp.


(c) Number of shares as to which such person has:

     (i)   sole power to vote or
           to direct the vote          0             0           0


     (ii)  shared power to vote
           or to direct vote           3,707,400     3,707,400   3,707,400

    (iii)  sole power to dispose or
           to direct disposition of    0             0           0

     (iv)  shared power to dispose or
           to direct disposition       3,707,400     3,707,400   3,707,400


Item 5.    Ownership of Five Percent or Less of a Class.

           Inapplicable.

Item 6.    Ownership of More than Five Percent on Behalf of Another Person.

           Inapplicable.

Item       7. Identification and Classification of the Subsidiary which Acquired
           the Security Being Reported On By the Parent Holding Company.

           Continental  Casualty Company,  an Illinois insurance company (IC).
           (See Exhibit 1.)

Item 8.    Identification and Classification of Members of the Group.

           Inapplicable.

Item 9.    Notice of Dissolution of the Group.

           Inapplicable.


<PAGE>




Item 10.   Certification of CNA Financial Corporation.

By signing below I certify  that,  to the best of my knowledge  and belief,  the
securities  referred to above were  acquired in the ordinary  course of business
and were not  acquired for the purpose of and do not have the effect of changing
or  influencing  the  control  of the  issuer  of such  securities  and were not
acquired in connection with or as a participant in any transactions  having such
purposes or effect.

After reasonable  inquiry and to the best of my knowledge and believe, I certify
that the information set forth in this statement is true, complete and correct.


February 14, 2001
             Date

/s/ Jonathan D. Kantor
             Signature

Jonathan D. Kantor
Senior Vice President, General Counsel and Secretary




Item 10.   Certification of Loews Corporation.

By signing below I certify  that,  to the best of my knowledge  and belief,  the
securities  referred to above were  acquired in the ordinary  course of business
and were not  acquired for the purpose of and do not have the effect of changing
or  influencing  the  control  of the  issuer  of such  securities  and were not
acquired in connection with or as a participant in any transactions  having such
purposes or effect.

After reasonable  inquiry and to the best of my knowledge and believe, I certify
that the information set forth in this statement is true, complete and correct.


February 14, 2001
             Date




/s/     Barry Hirsch
             Signature

Barry Hirsch
Senior Vice President, Secretary and General Counsel




Item 10.   Certification of Continental Casualty Company.

By signing below I certify  that,  to the best of my knowledge  and belief,  the
securities  referred to above were  acquired in the ordinary  course of business
and were not  acquired for the purpose of and do not have the effect of changing
or  influencing  the  control  of the  issuer  of such  securities  and were not
acquired in connection with or as a participant in any transactions  having such
purposes or effect.

After reasonable  inquiry and to the best of my knowledge and believe, I certify
that the information set forth in this statement is true, complete and correct.


February 14, 2001
             Date

/s/ Jonathan D. Kantor
             Signature

Jonathan D. Kantor
Senior Vice President, General Counsel and Secretary


<PAGE>





                                    Exhibit 1

Loews  Corporation  holds  in  excess  of  87% of the  equity  of CNA  Financial
Corporation.

CNA  Financial  Corporation  owns 100% of the relevant  subsidiary,  Continental
Casualty Company,  an Illinois  domiciled  insurance  company (IC).  Continental
Casualty Company is the direct owner of the position being reported.



                                    Exhibit 2

Each of the  undersigned  hereby agrees that the Schedule 13G filed  herewith is
filed  jointly,  pursuant to Rule 13d-l(f) of the Securities and Exchange Act of
1934, as amended, on behalf of each of the undersigned.


CONTINENTAL CASUALTY COMPANY

/s/ Jonathan D. Kantor
             Signature

Jonathan D. Kantor
Senior Vice President, General Counsel and Secretary


CNA FINANCIAL CORPORATION

/s/ Jonathan D. Kantor
             Signature

Jonathan D. Kantor
Senior Vice President, General Counsel and Secretary


LOEWS CORPORATION

/s/ Barry Hirsch
             Signature

Barry Hirsch
Senior Vice President, Secretary and General Counsel