An email sent from Paul Tucker, then Executive Director for Markets at the Bank of England, to Barclays Vice President Bob Diamond shows that Mr Tucker was "struck" that Barclays was issuing bonds "at around 140 over gilts". "That's a lot," he wrote.
The pair then arranged a time to discuss the matter face-to-face or by phone, although it is not clear whether that conversation took place.
In another exchange, in to which the then chief executive of Barclays John Varley was copied, Paul Tucker asked to talk to either official "about Libor". He wrote it is "a slightly sensitive point".
The email is one of several released to John Mann MP following his Freedom of Information request for the Bank of England.
Mr Tucker is due to be questioned by the Treasury Select Committee later today about his knowledge of the Libor rate-rigging scandal.
Paul Tucker will face questions from members of the Treasury Select Committee today about an alleged conversations he had with Bob Diamond and politicians about rigging the Libor rate.
Mr Tucker has been the Deputy Governor of the Bank of England since early 2009. He has been widely-tipped as the most likely successor to the current governor Mervyn King.
He joined the the Bank of England after graduating from Cambridge University in 1980 and has headed a number of divisions within the bank. Since 2002, he has served on the bank's Monetary Policy Committee, which has the responsibility of setting interest rates.
Today, he will be questioned about how much the Bank of England - one of the City's main regulators - knew about Libor rate-rigging, and why he appeared to imply that Barclays should lower its rate in an alleged phone conversation with Bob Diamond in 2008.