BOB Diamond will today face questions from parliament on his role in the Libor-fixing scandal, following a dramatic 12 hours that began with his resignation as chief executive of Barclays and ended with the Bank of England battling to keep itself out of the crisis.

Diamond’s resignation was announced early yesterday morning after he decided overnight that his position had become unsustainable.

“The external pressure placed on Barclays has reached a level that risks damaging the franchise – I cannot let that happen,” he said in a statement.

Barclays declined to comment on claims that the decision was made after Bank of England governor Mervyn King and Lord Turner, the chairman of the Financial Services Authority (FSA), personally contacted directors and encouraged Diamond to step down.

But it was a sudden change in direction for the Barclays board, which had originally decided its chief executive would fight on after chairman Marcus Agius resigned in an attempt to defuse the situation.

Agius responded to the turn of events by delaying his departure and instead taking on the new role of executive chairman, tasked with finding a new chief executive and running the company in the interim period.

“What I did yesterday was indicate my intention to resign. I was not resigning with immediate effect. I am still chairman and I still have the full confidence of the board. I am the obvious person to lead the succession,” he explained.

But by lunchtime he found himself with an additional board vacancy as chief operating officer Jerry del Missier also quit – just 11 days after taking up the position.

“Jerry was the most senior officer who gave instructions to lower the Libor rate,” Agius told reporters. “That obviously put him in a very difficult position.”

Barclays then released an internal 2008 memo written by Diamond, then head of the Barclays Capital investment banking division, which suggests that Paul Tucker, the deputy governor of the Bank of England, was aware of irregularities in Libor submissions made by Barclays and other banks.

“Mr Tucker stated...that while he was certain we did not need advice, that it did not always need to be the case that [the bank’s Libor submissions] appeared as high as we have recently,” Diamond wrote in an email to fellow executives.

Bank of England officials declined to comment on the content of the email but repeated its position that two separate probes on both sides of the Atlantic had found no evidence that Tucker had encouraged the falsification of Libor submissions. City A.M. understands that Paul Tucker was questioned by investigators as part of the probe that led to Barclays’ record-breaking £290m fines.

Yesterday the FSA confirmed that its investigators “were aware of this email” but concluded “no instruction was given by the Bank in relation to Libor submissions”.

But the memo’s claim that Tucker was also receiving calls from “senior” Whitehall staff on the issue raised the possibility that members of the previous Labour government could be drawn into the affair.

When Diamond suggested that Tucker should tell these Whitehall staff that many other banks were also distorting their Libor submissions, the Bank of England official allegedly replied: “oh, that would be worse”.

Last night Labour politicians, including shadow chancellor Ed Balls and former chancellor Alistair Darling, queued up to claim they were not involved in discussions surrounding the Libor rate as the focus switched to the previous administration’s role.

Attention will now shift to Diamond’s appearance at today’s Treasury select committee, where his answers will enjoy the legal immunity provided by parliamentary privilege.

Labour MP John Mann, a member of the committee, told City A.M. that he will use the opportunity to demand Barclays call in external investigators to deal with the “systematic fraud that was being carried out in their trading rooms”.

“I want to know why Barclays haven’t brought in the Serious Fraud Office to have these criminals arrested,” he said. “At their weekly executive meetings they got reports on Libor. So how come Bob Diamond was so incompetent that he couldn’t spot market manipulation for three years?” He also predicted that “another 20 banks, including RBS” will face similar charges.