Barclays chief executive Bob Diamond has resigned with immediate effect in the wake of the rate-rigging scandal.
The American banker, who has faced mounting calls to step down, said: "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."
The move comes after Barclays was fined £290 million by UK and US regulators for manipulating the Libor, the rate at which banks lend to each other.
Chairman Marcus Agius, who announced his intention to resign over the affair yesterday, will lead the search for a new chief executive immediately, Barclays said.