Barclays has been told to pay up after it was discovered they had been influencing the Libor and the Euribor as far back as 2005, which may have led to customers being charged too much for credit card and mortgage loans.

The bank's chief executive Bob Diamond has faced calls to resign over the transgressions and will face a grilling from parliament. In response, he said he and his top executives will forgo any multi-million pound bonus “to reflect our collective responsibility as leaders.”

Lord Oakeshott, the former Liberal Democrat Treasury spokesman said: “If Bob Diamond had a scintilla of shame, he would resign, and if Barclays had an inch of backbone between them they would sack him.”

In a statement, Barclays said the actions “fell well short of standards,” and admitted to “misconduct.”

While it is not yet clear if the bank succeeded in its underhand tactics, the repercussions could be seismic.

Libor is the benchmark rate that is used for contracts supplied by the world's biggest banks across the world, worth hundreds of millions of pounds, and is also used a reference for corporate lending.

Tracey McDermott, director of enforcement at FSA said they started looking at Barclays towards the end of 2009 and continued into early 2010.

“We found the misconduct is some of the most serious we've ever seen, and that's why the penalty we've imposed is such a serious one,” she told the BBC. “It's really important for the integrity of that rate to be preserved and that the market is confident the rate reflects what it is supposed to, which is the amount at which banks can borrow from each other.”

The FSA and the US Commodity Futures Trading Commission announced there are still ongoing investigations into the misuse of Libor.