Ken Costa, who joined Lazard as international chairman in October, has taken just weeks to win his first mandate after picking up the brief to advise Luqman Arnold, a former colleague at Swiss bank UBS, on his pursuit of stricken UK lender Northern Rock.

Arnold, the former chief executive of Abbey National, said in a regulatory news statement this morning that he was preparing a proposal for the board of Northern Rock. He made the approach via Olivant, the investment company he founded last year.