Exhibit 99(b)

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We hereby consent to the incorporation by reference in the Registration Statement on Form S-8 (No. 333-68438) of OneBeacon Insurance of our report dated June 28, 2005 relating to the financial statements of the OneBeacon Insurance Savings Plan, which appears in this Form 11-K.

/s/ PricewaterhouseCoopers LLP

PricewaterhouseCoopers LLP

Boston, Massachusetts

June 28, 2005