The ousted Barclays chief executive Bob Diamond is facing fresh pressure after the chairman of the House of Commons Treasury select committee described some of his evidence to MPs yesterday as "implausible", as the row grew over who was at the heart of manipulation of interest rates during the credit crisis.

Andrew Tyrie, who could take charge of a parliamentary inquiry into Britain's banking industry if MPs can reach agreement today, ratcheted up the pressure on Diamond by writing to Barclays over some of his evidence.

Hours after Diamond denounced the behaviour of some of his staff as "reprehensible", Tyrie said he would be asking Barclays for correspondence from the Financial Services Authority about its assessment of Diamond.

Tyrie said: "I think, cumulatively, the whole package looks somewhat implausible."