Alistair Darling has warned that other major banks face a sharp reduction in profits, following the resignation of Citigroup's boss.Charles Prince has quit as chairman and chief executive of what is the world's largest bank.His departure ends a difficult four-year tenure marked by heavy management turnover, questions over strategy and mounting losses from bad loans and mortgages.The Chancellor insisted that "transparency" had to be improved in the wake of the global credit crunch, but stressed that UK banks had strong balance sheets and the fundamental economic position was strong.Mr Prince's resignation comes just three weeks after Citigroup announced a $6.5 billion (£3.25 billion) write-down for loan losses, subprime mortgages and other debt.It also comes five days after Merrill Lynch removed its own chief executive, Stanley O'Neal, following an $8.4 billion (£4.2 billion) write-down.Citigroup has said it wants to boost capital, but the problems are spurring more calls for the bank to be broken up because it is too unwieldy."I just don't think (Prince) was the right person to run Citigroup," said Jim Huguet, co-chief executive of Great Companies LLC in Florida and a Citigroup shareholder."He was brought in to fix their legal problems because he's a lawyer, but they need someone who is capable of really building the business, and I don't think that's Prince's forte."© Independent Television News Limited 2007. All rights reserved.