UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM 13F FORM 13F COVER PAGE Report for the Calendar Year or Quarter Ended: September 30, 2008 ----------------------- Check Here if Amendment / /; Amendment Number: --------- This Amendment (Check only one.): / / is a restatement. / / adds new holdings entries. Institutional Investment Manager Filing this Report: Name: OneBeacon Insurance Group, Ltd. ------------------------------- Address: 601 Carlson Parkway ------------------------------- Minnetonka, Minnesota 55305 ------------------------------- U.S.A. ------------------------------- Form 13F File Number: 028-12951 --------------------- The institutional investment manager filing this report and the person by whom it is signed hereby represent that the person signing the report is authorized to submit it, that all information contained herein is true, correct and complete, and that it is understood that all required items, statements, schedules, lists, and tables, are considered integral parts of this form. Person Signing this Report on Behalf of Reporting Manager: Name: Ann Marie Andrews ------------------------------- Title: Chief Accounting Officer ------------------------------- Phone: (781) 332-7000 ------------------------------- Signature, Place, and Date of Signing: /s/ Ann Marie Andrews Canton, Massachusetts November 12, 2008 ------------------------------- --------------------- ----------------- [Signature] [City, State] [Date] Report Type (Check only one.): / / 13F HOLDINGS REPORT. (Check here if all holdings of this reporting manager are reported in this report.) / / 13F NOTICE. (Check here if no holdings reported are in this report, and all holdings are reported by other reporting manager(s).) /X/ 13F COMBINATION REPORT. (Check here if a portion of the holdings for this reporting manager are reported in this report and a portion are reported by other reporting manager(s).) List of Other Managers Reporting for this Manager: [If there are no entries in this list, omit this section.] No. Form 13F File Number Name 1. 028-04685 Prospector Partners, LLC FORM 13F SUMMARY PAGE Report Summary: Number of Other Included Managers: 1 -------------------- Form 13F Information Table Entry Total: 31 -------------------- Form 13F Information Table Value Total: 31,282 -------------------- (thousands) List of Other Included Managers: Provide a numbered list of the name(s) and Form 13F file number(s) of all institutional investment managers with respect to which this report is filed, other than the manager filing this report. No. Form 13F File Number Name 1 28 - N/A Copley Square Capital Management, LLC FORM 13F INFORMATION TABLE COLUMN 1 COLUMN 2 COLUMN 3 COLUMN 4 COLUMN 5 COLUMN 6 COLUMN 7 COLUMN 8 ------------------------- ---------------- --------- -------- ---------------------- ------------ ---------- ---------------------- VALUE SHRS OR SH/ PUT/ INVESTMENT OTHER VOTING AUTHORITY NAME OF ISSUER TITLE OF CLASS CUSIP (x$1000) PRN AMT PRN CALL DISCRETION MANAGERS SOLE SHARED NONE ------------------------- ---------------- --------- --------- --------- ----- ------ ------------ ---------- ------ -------- ------ Alcoa Com 013817101 338,700 15,000 x x American INTL Group Inc Com 026874107 66,600 20,000 x x Automatic Data Proc Com 053015103 855,000 20,000 x x Bank New York Mellon Com 064058100 1,791,900 55,000 x x Cardinal Health Inc Ohio Com 14149Y108 246,400 5,000 x x Colgate Palmolive Com 194162103 1,883,750 25,000 x x CVS Caremark Corp Com 126650100 2,019,600 60,000 x x Embraer Empresa Bras ADR ADR 29081M102 270,100 10,000 x x Goldman Sachs Group Inc. Com 38141G104 640,000 5,000 x x Hartford Finl Svcs Group Com 416515104 819,800 20,000 x x Honda Motor ADR New AMERN SHS 438128308 1,204,400 40,000 x x Honeywell Intl Inc Del Com 438516106 2,160,600 52,000 x x Illinois Tool Works Inc Com 452308109 1,778,000 40,000 x x Kraft Foods Inc VA CL A CL A 50075N104 818,750 25,000 x x L-3 Communications Hldgs Com 502424104 2,458,000 25,000 x x Marathon Oil Corp Com 565849106 1,196,100 30,000 x x Monsanto Co New Del Com Com 61166W101 989,800 10,000 x x Nucor Corporation Com 670346105 1,185,000 30,000 x x Patriot Coal Corp Com 70336T104 29,050 1,000 x x Peabody Energy Corp Com Com 704549104 675,000 15,000 x x Petrleo Bras VTG SPD ADR ADR 71654V408 439,500 10,000 x x Plum Creek Timber Co Inc Com 729251108 1,246,500 25,000 x x Safeway Inc New Com 786514208 237,200 10,000 x x Staples Inc Com 855030102 450,000 20,000 x x TJX Cos Inc New Com 872540109 1,526,000 50,000 x x Toronto Dominion Bank Com 891160509 609,900 10,000 x x United Techs Corp Com Com 913017109 900,900 15,000 x x Wellpoint Inc Com 94973V107 1,169,250 25,000 x x Weyerhaeuser Co Com 962166104 605,800 10,000 x x Yum Brands Inc Com 988498101 1,304,400 40,000 x x 3M Company Com 88579Y101 1,366,200 20,000 x x