Former head of Barclays, Bob Diamond, has apologized for the "reprehensible" behavior of his traders who fixed interest rates. However, he told British lawmakers that his bank had been unfairly singled out after coming forward to admit wrongdoing.

The 60-year-old Diamond quit this week after Barclays agreed to pay nearly half a billion dollars in fines after found manipulating the interest rates at the heart of the global financial system. The man who was one of the world's highest paid and most powerful financial executives with an aggressive reputation until Tuesday acknowledged "inexcusable" behavior among his group's traders.

"When I read the e-mails from those traders, I got physically ill," Diamond said. "That behavior was reprehensible, it was wrong. I am sorry, I am disappointed and I am also angry."

Diamond went on to remark that those involved in rigging interest rates would be subject to criminal investigation and should be "dealt with harshly".

"This week the focus has been on Barclays because they were the first," Diamond said, describing years of cooperation with regulatory agencies to uncover the practice.

"I think it's a sign of the culture of Barclays that we were willing to be first, we were willing to be fast and we were willing to come out with this."

Andrew Tyrie, chairman of the committee, was equally critical: "Bob Diamond gave a number of what I thought were, at least cumulatively, somewhat implausible replies," he told Sky News.

"My general impression was that it was not the kind of gun fight at the O.K. Corral that we had anticipated before the event," said Richard Reid of the International Centre for Financial Regulation, a think tank. "No real smoking gun was found."

"They were clearly involved and we just haven't heard the full facts, I don't think, of who knew what when," Britain's finance minister, George Osborne, said in an interview with the Spectator.