When UBS persuaded Oswald Grübel to come out of retirement to become its chief executive, the former Credit Suisse head knew he was signing up for the most challenging job in European banking.

Having helped to define investment banking and credit management in the boom years of the 1990s and beyond, UBS was on its knees. Its share price had crashed to Sfr10 from a Sfr75 high 18 months before.