Jamie Dimon, chief executive of JPMorgan Chase, told employees in a memo that the bank had spent a billion dollars to tackle its regulatory issues as he sought to pre-empt negative publicity ahead of an expected fine for the $6bn London Whale trading loss.

Amid mounting calls in the US Congress for the country’s biggest financial institutions to be streamlined or broken up, Mr Dimon told staff in the widely-circulated memo that making the business simpler was a “key initiative”.

The $6bn losses incurred in last year’s trading debacle have helped stoke criticism that banks including JPMorgan, which employs 260,000 people, have become “too big to manage”. The losses occurred in an obscure credit portfolio that received scant attention from analysts and supervisors.