Mr Tucker, a forerunner for the top position at the Bank when Sir Mervyn King steps down, faces a series of questions from MPs on the Treasury Select Committee over alleged conversations he had with Barclays on the key interbank lending rate known as the Libor.
John Mann MP received records of the emails following a Freedom of Information request to the Bank of England. He has said that the Bank may be in contempt of Parliament for not releasing the emails sooner.
Mr Tucker reiterated that he had received calls from a number of senior figures within Whitehall to question why Barclays was always towards the top end of Libor pricing ... Mr Tucker stated the levels of calls he was receiving from Whitehall were 'senior' and that while he was certain we did not need advice, that it did not always need to be the case that we appeared as high as we have recently.
In his appearance before the Treasury Select Committee, Mr Diamond said he "didn't feel it was an instruction" to lower the Libor rates, but that he was left "confused" by the conversation.
See ITV News' Political Editor Tom Bradby's report:
He 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."
Mr Tucker will be questioned about whether figures within the Bank of England were aware that rate-rigging was going on, and if not, whether they took their eyes off the ball.
Attention will also focus on who the "senior figures within Whitehall" cited in the memo refer to. Mr Diamond refused to "speculate" on their identities.
Meanwhile, the phrase has triggered a spate of finger-pointing in Whitehall as politicians from the Labour government of the day sought to distance themselves from the affair.
Meanwhile, the Labour leader Ed Miliband delivered a speech this morning outlining how he would seek to reform ethics in banking. He pointed to the Libor rate-fixing scandal as vindication of his much-criticised attack last year on "predatory" capitalism.
The committee will question Barclays chairman Marcus Agius on Tuesday morning. No other witnesses have been called so far.