Barclays Chief Executive, Bob Diamond

Bob Diamond has quit as chief executive of Barclays bank in a shock twist to the rate-rigging scandal, reports Sky News.

Marcus Agius, who announced his intention to resign as chairman only yesterday, is to take over the running of the bank while a successor to Diamond is found.

The announcement was unexpected in that Diamond had made it clear to staff in a memo 24 hours earlier that he had no intention of falling on his sword - saying it was his responsibility to restore the bank's reputation.

The American, who has faced mounting calls to step down, said this morning: "The external pressure placed on Barclays has reached a level that risks damaging the franchise."

He added: "I am deeply disappointed that the impression created by the events announced last week about what Barclays and its people stand for could not be further from the truth."

Barclays was fined £290m by UK and US regulators for manipulating the interbank lending rate, Libor.

It has since emerged that an estimated 12 other lenders in the UK and elsewhere in the world are also under investigation.