“Only two people in this firm would actually matter if they fell under a bus tomorrow,” said one senior JP Morgan banker earlier this year, “Jamie Dimon and Bill Winters.”

Bill Winters did not fall under a bus, but, nevertheless, staff at the bank's London office were left stunned last Tuesday when they received a memo announcing that the man many credit with turning the firm into one of the world's top investment banks was to leave after 25 years.