Prime Minister David Cameron has said that Barclays Bank management has "serious questions" to answer over how it manipulated banking lending rates.

Barclays was fined £290m (US$450m) after an investigation into claims that several banks manipulated the Libor rate at which they lend to each other.

The Chancellor George Osborne confirmed that HSBC, RBS, Citigroup and UBS are also under investigation.

The scandal hit Barclays shares, which ended yesterday trading down 15.5 per cent.

Other banks shares fell as well, with RBS losing 11.5 per cent, Lloyds down 3.9 per cent, and HSBC giving up 2.6 per cent.

Barclays had acknowledged on Wednesday that its actions between 2005 and 2009 had fallen "well short of standards".

Investigators say that Barclays' traders lied to make the bank look more secure during the financial crisis and, sometimes—working with traders at other banks—to make a profit.

Who was responsible?

Cameron said: "The whole management team have got some serious questions to answer. Let them answer those questions first.

"Who was responsible? Who was going to take responsibility? How are they being held accountable?"

Business Secretary Vince Cable said that while it would be "seriously premature" to decide now whether Mr Diamond should be sacked, he added that the Government did have powers to disqualify directors.

"If the facts suggested action—and obviously we would be subject to legal advice; this is a legal process—then indeed that could well follow," he said.

In a statement to the House of Commons, Chancellor Osborne said: "The FSA report is a shocking indictment of the culture at banks like Barclays in the run-up to the financial crisis."

"Through 2005, 2006 and early 2007 we see evidence of systematic greed at the expense of financial integrity and stability and they knew what they were doing," he said.

Currently fines paid by banks help to bring down the levy other financial firms pay to run the regulator.

The Chancellor said the government is looking to change that to make sure the taxpayer benefits from the fines.

Labour party leader, Ed Miliband, said: "This cannot be about a slap on the wrist.

"The people that have done the wrong thing in this case should face the full force of the law... including criminal prosecutions."

Regulators say that Barclays manipulated how it reported the interest rates at which banks lend to each other to benefit their traders and financial status.

Tracey McDermott, director of enforcement at the FSA, which imposed fines alongside the US financial regulator, told the BBC that "we need to look at each case on its own particular facts but the initial indications are that Barclays was not the only firm that was involved in this."