Slaughters corporate head Frances Murphy is leading the advice for Santander as part of an integrated team that includes Uría Menéndez in Spain and Davis Polk & Wardwell in the US.
A&O corporate partner Mark Wippell is leading the team advising Alliance & Leicester.
Spanish bank Santander already owns Abbey National, now known as Abbey, having acquired it in 2003. At that time Santander turned to Clifford Chance while Abbey was advised by Slaughters.
The current exchange offer for Alliance & Leicester is expected to complete in or around October 2008.
In addition to Murphy, Slaughters is fielding a team including corporate partners Roland Turnill and Andrew Jolly with associates James Cooney, Jonathan Stewart and Victoria Ballantyne.
Other advice is provided by Slaughters tax partner Steve Edge, financial regulation partner Jan Putnis and competition partner Bertrand Louveaux, with associate Steve Smith assisting. Pensions and employment partner Roland Doughty is also involved.
The Uría Menéndez team was led by partner Salvador Sánchez-Terán and Davis Polk & Wardwell in New York by partner Nicholas Kronfeld.
In addition to Wippell, A&O’s team advising Alliance & Leicester includes corporate partners Louise Wolfson and Anna Buscall, senior associates Colin Bole and Krishna Raman, and associates Nicholas Manassei and Elvan Hussein. A&O corporate partner Juan Barona and tax partner Carols Albinana advised in Spain.
All firms declined to comment.