Bank of England deputy governor Paul Tucker will attempt to clear up his involvement in the rate-rigging affair on Monday former Barclays boss Bob Diamond dragged the deputy into the scandal.
Mr Tucker, a forerunner for the position of Bank governor when Sir Mervyn King steps down, faces a series of questions from MPs on the Treasury Select Committee over discussions he had with Barclays on the key interbank lending rate known as the Libor.
The deputy governor found himself in the spotlight after Mr Diamond disclosed a note of a phonecall between the two men, in which Mr Tucker appeared to encourage the bank to submit lower Libor submissions in light of concerns from senior Whitehall figures.
Meanwhile, the fierce debate over banking ethics will rage on as Labour leader Ed Miliband delivers a speech on his vision for the sector.
He will point to the Libor rate-fixing scandal as vindication of his much-criticised attack last year on "predatory" capitalism and promise wide-ranging action.
Barclays has been the focal point for a row over banking culture after the bank was fined £290 million by UK and US regulators for manipulating the Libor, which affects mortgages and loans.
Mr Diamond, who resigned with immediate effect last Tuesday, told MPs he was left "confused" by the contentious phonecall with Mr Tucker.
But despite being unclear about his motives, Mr Diamond said his reaction to the conversation was "appreciation of Paul Tucker for doing his job".
Mr Diamond told MPs Mr Tucker relayed concerns from senior Whitehall figures - which he took to mean officials within Government - that Barclays' Libor rate was too high - which could be a sign of financial weakness at the bank.
Mr Diamond said there were 14 or 15 other banks, including nationalised lenders such as Royal Bank of Scotland, who he knew had a weaker financial position than Barclays and were still submitting lower Libor rates.
Outlining his interpretation of Mr Tucker's comments, he said: "He felt that our Libor rates, relevant to the other 15 posters, could be lower."
But he insisted he did not feel any action had been requested.
"I didn't feel it was an instruction," he said.
However, Mr Diamond's account of the conversation ultimately led to the then president of investment banking arm Barclays Capital, Jerry del Missier, telling staff to submit lower Libor.
Mr Miliband will say he would like to see Britain's top five high street banks broken up and forced to sell up to 1,000 branches to pave the way for two new privately run challenger banks to bolster competition in the sector.
Lloyds Banking Group is already selling off more than 600 branches, with Co-operative Bank currently in exclusive talks to form what would amount to one of the challenger banks included in Mr Miliband's overhaul.
The Opposition leader also wants a new code of conduct for the banks to follow, which would be supervised by an organisation similar to the British Medical Association.
In addition, Mr Miliband would like to see a specialist banking unit set up with the Serious Fraud Office to tackle the "weak and fragmented" approach to fraud investigations.
As the debate continues, pressure continues to build on Mr Diamond to waive at least part of a reported £17 million golden parachute deal, while the bank also considers spinning off Barclays Capital.
The bank's board is understood to have discussions with the Association of British Insurers, the trade group which represents billion of pounds of pension funds' investments, over plans to open negotiations with Mr Diamond over his exit pay.
Marcus Agius, who also announced his intention to step down but will remain until Mr Diamond's successor is found, will give evidence to MPs on Tuesday but is likely to tell them nothing has been decided.
Business Secretary Vince Cable yesterday said: "I think in view of what's happened, I would sincerely hope that the board of Barclays take a fairly strict view about this."
But Mr Cable added: "There isn't anything that the Government can do about it but I think in view of the shame that has been heaped on Barclays bank, I would be very, very surprised if the chairman and the board were to allow another outrage to occur."
More than £3.7 billion has been wiped off Barclays' market value since the Libor revelations.
The Serious Fraud Office on Friday launched a criminal investigation into alleged Libor-rigging at Barclays and the wider industry.
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