By Jonathan Davies

The Libor trader Tom Hayes has told a court that the practice was so common, the offer of a Mars bar was enough to get the rate changed.

Mr Hayes, the first person to go on trial for alleged manipulation of the key interest rate, explained to Southwark Crown Court that he once told a colleague: "Just give the cash desk a Mars bar and they'll set wherever you want."

On Wednesday, the court was shown numerous transcripts of traders' conversations on UBS' internal messaging system about fixing the Libor.

In one conversation, Mr Hayes suggested that there were a lot of traders trying to get it fixed. He said: "Very, very hard to price stuff with the fixes so manipulated and inconsistent."

"The fixes are manipulated?", responded the other trader.

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

In another conversation, the Libor is described as "literally a joke".

On Tuesday, Mr Hayes said that his senior managers knew about his actions.

The court was shown an email conversation between senior management at UBS which appears to show that they did know about his attempts to fix the rate.

It also shows that management had their reservations about Mr Hayes, describing him as "an immature, explosive person, who regularly loses his temper".

It read: "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?"