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.
Bob Diamond tonight angrily rejected suggestions that he misled MPs over regulators' concerns about activities at Barclays.
The Bank of England's Paul Tucker told MPs he refuted claims that he attempted to influence Barclays into manipulating the Libor rate.
MPs will be hoping the Deputy Governor of the Bank of England will shed some light on unanswered questions about rate-fixing at Barclays.