Davis Polk London partner Jeffrey Oakes and New York partner Arthur Long were brought into the deal by Slaughter and May, which is representing the Treasury on the rescue scheme.
Davis Polk is a member of Slaughter and May's best friend network.
A source close to the deal said: "It is a smaller yet crucial role because of the number of banks that are transforming into bank holding companies. Davis Polk is advising on a range of deals in the US related to this subject. This role fits well with the work the firm is doing in the US."
In the US Davis Polk partners Randall Guynn, Michael Kaplan and William Taylor are leading a team advising the New York Federal Reserve Bank on the impact of the capital injection into the US banking system.
The firm also won a lead role advising the New York Fed on an $85bn financial package for AIG last month (23 September) as well as the more recent $37.8bn financing for the insurer this month (9 October).
Cravath Swaine & Moore partners Robbins Kiessling and partner Philip Boeckman advised alongside Davis Polk on antitrust and documentation aspects of the deal.