Allen & Overy and Addleshaw Goddard were the main legal advisers in the merger of Barnsley Building Society with regional rival Yorkshire Building Society.
Barnsley, which turned to Addleshaws partners Adam Bennett (pictured), with Neil Woolhouse and Nick Hopper, sought a merger after being forced to write off up to £10m of money held in Icelandic banks.
Yorkshire instructed longstanding advisers Allen & Overy, led by Richard Slynn, who worked alongside the building society's head of legal John Faulkner.
The merger is subject to approval from the FSA and is expected to be completed by the end of the year.
Yorkshire will attempt to recover some of the money held in Kaupthing Singer & Friedlander and Heritable, a subsidiary of Landsbanki. Both banks have had their UK business put into administration by UK regulators.
Yorkshire is the country's third largest building society with assets of more than £20bn, compared to £376m at Barnsley.