Bob Diamond, who resigned as Barclays chief executive on Tuesday in the wake of the inter-bank interest rate-fixing scandal, has called the behaviour of those responsible "reprehensible".
He said he only found out about the true extent of the rigging this month.
Mr Diamond is being questioned by MPs about the rate rigging, specifically about who knew what and when.
MPs are also asking about the role of the Bank of England and the previous government in the rate-fixing.
Mr Diamond said he "loved" Barclays and had resigned to protect its reputation.
He defended the bank's actions to address the problems of rate-rigging when they were first discovered.
"As soon as we recognised [the problem] three years ago... we said 'let's get to the bottom of this'", he said.
The regulatory agencies involved, including the Financial Services Authority in the UK and US authorities, "applauded our co-operation", he added.
"This is not coming out in the court of public opinion."
'Judicial inquiry'
Earlier, the prime minister said Barclays' actions were "appalling".
David Cameron said it was "outrageous" that homeowners and businesses paid higher interest rates as a result of the bank's rate-rigging.
Labour leader Ed Miliband called for a two-part inquiry led by a judge, looking at both Libor and the wider culture of banking in the City, rather than the parliamentary inquiry proposed by the government. Mr Cameron said a judicial inquiry was not necessary.
In another development, the Bank's deputy governor, Paul Tucker, has asked to give evidence to the Treasury Select Committee in order to give his side of the story.
"Mr Tucker is keen to give evidence to the committee in order to clarify the position with regard to the events involving the Bank of England, including the telephone conversation with Bob Diamond on 29 October 2008," the Bank said in a statement.
On Tuesday, Barclays released Mr Diamond's note of a conversation in 2008 with Mr Tucker.
Mr Diamond writes that Mr Tucker told him of concerns among "senior figures within Whitehall" about why Barclays was setting its Libor rate - the rate at which banks lend to one another - at the "top end".
Subsequently, the Libor borrowing rates submitted by Barclays fell, potentially understating the extent of the bank's borrowing costs.
Wrong impression?
The Libor inter-bank rate plays a key role in global markets, affecting what banks, businesses and individuals pay to borrow money.
Barclays said in Tuesday's statement that Mr Diamond did not view his conversation with Mr Tucker as an instruction to change its rates submission.
However, after the phonecall with Mr Tucker, Mr Diamond relayed the conversation to Jerry del Missier, a senior executive in Barclays investment banking arm BarCap who resigned on Tuesday.
Barclays said: "Jerry del Missier concluded that an instruction had been passed down from the Bank of England not to keep Libors so high and he therefore passed down a direction to that effect to the [traders]."
'No recollection'
It is unclear who the "senior Whitehall" figures mentioned by Mr Diamond were.
Labour minister Baroness Vadera of Holland Park has said she has "no recollection" of speaking with anyone at the Bank of England about Libor, while former City minister Lord Myners told the BBC that he did not put pressure on the Bank of England or on Barclays to lower its Libor rate.
The manipulation of Libor took place in 2008, around the time Barclays was raising funds privately in the Middle East - rather than taking emergency loans from the government like a number of other major UK banks - following the credit crunch and the onset of the financial crisis.
Barclays is also being investigated for manipulating Libor rates to increase profits as far back as 2005.
The bank is also being investigated in the US, where the Department of Justice is undertaking criminal investigations into other financial institutions and individuals. Banks are also facing a number of class-action lawsuits relating to the manipulation of inter-bank lending rates.
Mr Diamond's resignation came less than a week after Barclays was fined £290m for its role in Libor manipulation.
