Exhibit 8.1

[Debevoise Letterhead]

March 13, 2013

Tower Group, Inc.

120 Broadway, 31^st Floor

New York, NY 10271

Tower Group, Inc. – Section 7874(b) Tax Opinion

To The Board of Directors:

We have acted as special United States tax counsel to Tower Group, Inc., a Delaware corporation (the “Company”), in connection with the merger (the “Merger”) of Condor 1 Corporation (“Merger Sub”), a direct wholly owned subsidiary of Canopius Mergerco, Inc. (“Delaware Purchaser”) and an indirect wholly owned subsidiary of Canopius Holdings Bermuda Limited (“CHBL”), with and into the Company (the “Transaction”) pursuant to an Agreement and Plan of Merger, dated as of July 30, 2012, among the Company, CHBL, Delaware Purchaser and Merger Sub, as amended by Amendment No. 1 to Agreement and Plan of Merger, dated as of November 8, 2012 among the Company, CHBL, Delaware Purchaser and Merger Sub (as so amended, the “Merger Agreement”).

As such, we have participated in the preparation of or reviewed the following documents (the “Basic Documents”):

Capitalized terms not defined herein shall have the meaning ascribed to them in the Merger Agreement.

In rendering this opinion:

No assurance can be given as to the effect on this opinion if any of the foregoing assumptions is or becomes inaccurate.

FACTS

The Company

The Company is a Delaware corporation formed in 1996, with its headquarters in New York, New York. The Company’s common stock is currently listed on NASDAQ. Through its insurance subsidiaries, the Company offers a broad range of commercial, specialty and personal property and casualty insurance products and services to businesses in various industries and to individuals throughout the United States.

CHBL

CHBL is a privately held exempted company formed under the laws of Bermuda in 2007. Immediately prior to its sale to the Third Party Investors described below, CHBL was a wholly owned subsidiary of CGL, a privately owned insurance holding company domiciled in Guernsey, Channel Islands. CHBL is the direct holding company of Canopius Bermuda Limited (“CBL”) a Class 3A Bermuda reinsurance company, which writes structured reinsurance treaty business and provides capital support to CGL’s underwriting operations at Lloyd’s of London.

The Third Party Sale

Immediately prior to the consummation of the Merger, CGL will sell 100% of the shares of CHBL in a private placement to the Third Party Investors (the “Third Party Sale”). The Third Party Investors will pay CGL an amount equal to the sum of the “target TNAV amount” (as defined in the S-4) plus an additional amount equal to the agreed value of the retained business (approximately $7.9 million). The Third Party Investors will not purchase any shares in CHBL from CHBL. Immediately after the Third Party Sale (and immediately prior to the Merger), the Third Party Investors will own 100% of the outstanding equity of CHBL.

The Merger

Pursuant to the Merger Agreement, Merger Sub will merge with and into the Company, with the Company surviving. As a result of the Merger, each issued and outstanding share of the Company’s common stock will be cancelled and converted

automatically into the right to receive a number of common shares of CHBL (which, after the Merger, we refer to as “Tower Ltd.”) equal to the “stock conversion number” (as defined in the S-4). The stock conversion number is determined by a variety of factors, including the target TNAV amount of CHBL, the closing price per share of the Company’s common stock on NASDAQ on the date that the Third Party Sale was priced, and the discount negotiated by the Third Party Investors in the Third Party Sale. As a result of the Merger, the Company will become a wholly owned subsidiary of Delaware Purchaser, and an indirect wholly owned subsidiary of CHBL. Immediately after the Merger, CHBL will be owned by the Third Party Investors and the former shareholders of the Company.

ASSUMPTIONS

In rendering this opinion we have assumed that:

CONCLUSION

Based upon the foregoing and subject to the limitations, qualifications and assumptions set forth herein, we are of the opinion that the Merger should not cause Tower Ltd. to be treated as a U.S. corporation under section 7874(b) of the Internal Revenue Code of 1986 (as amended from time to time, the “Code”).

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We have not independently undertaken to verify the accuracy or completeness of any of the factual matters, representations or assumptions referred to herein or set forth in the Representation Letters. In the event that any one or more of the facts, statements, representations or assumptions referred to herein or set forth in the Representation Letters are inaccurate or incomplete in whole or in part, the conclusion reached in this opinion letter may be incorrect.

Our opinion is based upon the Code, Treasury regulations (including proposed Treasury regulations) issued thereunder and administrative and judicial interpretations thereof, all as in effect on the date hereof. No assurance can be given that any of the foregoing authorities will not be modified, revoked, supplemented or overruled, possibly with retroactive effect, that the Internal Revenue Service (the “IRS”) will agree with this opinion or that, if the IRS were to take a contrary position, such position would not ultimately be sustained by the courts.

We are issuing this opinion solely for your benefit and, without our prior written consent, this opinion may not be (i) relied upon by any other person, (ii) quoted in whole or in part or (iii) referred to in any financial statements or other documents provided to third parties.

This opinion is limited to the matters specifically addressed herein and no other opinion is implied or may be inferred. Additional issues may exist that could affect the U.S. federal tax treatment of the Merger and related transactions. This opinion does not consider or provide a conclusion with respect to any such additional issues. With respect to any U.S. federal tax issues not addressed herein, this opinion was not written, and cannot be used by any taxpayer, for the purpose of avoiding penalties that may be imposed on the taxpayer under U.S. federal tax law.

This opinion is rendered only as of the date hereof, and we assume no responsibility to advise you or any other person of facts, circumstances, changes in law, or other events or developments that hereafter may occur or be brought to our attention and that may affect the conclusion expressed herein.

This opinion was not intended or written to be used, and it cannot be used by any taxpayer, for the purpose of avoiding penalties that may be imposed on the taxpayer under U.S. Federal tax laws. This opinion was written to support the promotion or marketing of the transaction(s) or matters(s) addressed herein. Each taxpayer should seek advice based on the taxpayer’s particular circumstances from an independent tax advisor.

We hereby consent to the filing of this opinion as an exhibit to Tower Ltd.’s Current Report on Form 8-K filed on March 13, 2013, and to the references to our firm therein. In giving such consent, we do not thereby concede that we are within the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Securities and Exchange Commission thereunder.