Image copyright Reuters Image caption Tom Hayes said a Mars bar would be acceptable currency to a rate setter

A court has heard that manipulating Libor rates was so commonplace an offer of a Mars bar could get it changed.

Tom Hayes, who worked for UBS and Citigroup, told a fellow trader: "Just give the cash desk a Mars bar and they'll set wherever you want."

Mr Hayes is the first person to face a jury trial for manipulating the key interest rate, used to set trillions of pounds of investments.

He denies eight counts of conspiracy to defraud between 2006 and 2010.

Throughout Wednesday's session, the court was shown dozens of pages of transcripts of exchanges between traders using UBS's internal messaging system.

The conversations - matey in tone - all related to moving Libor rates, said Mr Hayes, to assist the traders' and banks' commercial interests, something he said he found it hard to see as wrong.

In one chat, Mr Hayes suggests the market is rife with dealers attempting to influence rates: "Very, very hard to price stuff with the fixes so manipulated and inconsistent."

His correspondent replies: "The fixes are manipulated?"

"Yes, of course they are," says Mr Hayes. "Just give the cash desk a Mars bar and they'll set wherever you want."

Another chat session described Libor as "literally a joke".

'Shocked'

He has alleged throughout his trial that rate-rigging was rife and said on Tuesday that senior managers, even the chief executive of the bank, knew all about it.

My Hayes told the court on Wednesday that only once had anyone expressed any concern about the matter.

He said he was "shocked" when his manager phoned him asking him not to mention Libor rate-setting in any emails, saying that to be contacted by phone was highly unusual.

The phone call had come in 2009, towards the end of Mr Hayes's time at UBS.

He told the court: "I was shocked by the call. I thought, 'What was that all about?'" he said.

"It wasn't the usual way of communication at UBS."

He added that the manager had later explained he had overreacted because of the intense focus on Libor rate-setting at the time.

'Explosive'

The court was also shown an email exchange between senior management appearing to show they had reservations about Mr Hayes.

One describes him as "an immature, explosive person, who regularly loses his temper".

"He speaks to the brokers who are usually asked by the others where to set Libor. Big deal. He does know some of the traders at other banks from his London days, but personally I find it embarrassing when he calls up his mates to ask for favours on high/low fixings. It makes UBS appear to manipulate others to suit our position. What's the legal risk to UBS asking others to manipulate rates?"

The Libor scandal has seen a number of the world's leading banks fined for manipulating rates - traditionally to price loans between themselves.

It used to be set by a number of banks simply telling each other what rate they were prepared to use. Since then, the method has been changed to make it less open to rigging.

The trial continues.