The bank's former boss said the claims were "totally unfair and unfounded" - and indicated he was ready to appear before the Commons Treasury Select Committee again to defend his reputation.
The rejection of the claims came in a letter sent following an evidence session with Barclays chairman Marcus Agius.
"Having watched the committee's session today I was dismayed that you and some of your fellow committee members appeared to suggest that I was less than candid with the committee last week," he wrote.
"Any such suggestion would be totally unfair and unfounded."
However, speaking to Sky's Jeff Randall, the committee's chairman Andrew Tyrie stuck to his guns, questioning Mr Diamond's honesty on the day of the grilling.
He said: "We felt he had been economical with the truth and we had difficulty getting to the bottom of some of the questions we asked him.
"I still feel that on a good number of issues we did not get to the bottom of where we should have done."