Former Barclays traders Stylianos Contogoulas, Jay Merchant, Alex Pabon and Ryan Reich and former Barclays rate submitter Jonathan Mathew have all pleaded not guilty to a charge of conspiracy to defraud by manipulating U.S. dollar Libor rates between June 2005 and September 2007.

Britain's Serious Fraud Office (SFO), the agency in charge of prosecuting complex financial crime, alleges the five men dishonestly agreed to procure or make submissions of rates in the dollar Libor-setting process which were false or misleading in order to benefit their trading positions.

Each count carries a maximum jail sentence of 10 years.

On April 7, the prosecution told the court that Merchant alleged to the SFO in March 2014 that top bosses at Barclays, including Bommensath, had approved and condoned the practice of making such Libor requests.

Bommensath, who was global head of fixed income at Barclays at the time of the indictment period, told the jury in London that he was never aware of or condoned the practice.

He was appearing for the first time in the trial as a prosecution witness.

The London interbank offered rate, known as Libor, is a benchmark for about $450 trillion of financial contracts worldwide, from complex derivatives to student loans.

French-educated Bommensath, who started his banking career at Banker's Trust as a trader, had moved to New York from London by the autumn of 2006 in an expanded role that saw him responsible for up to 1,000 employees, he told the court.

Bommensath told the jury that Merchant never reported to him and was "at least" two levels below him. He once played tennis with Merchant, who was a very good player, but otherwise he never socialised with him, Bommensath added.

FUN AND GAMES

Bommensath also told court that he had not been aware at the time of Barclays submitting lower Libor rates during the 2007-2008 financial crisis - known as lowballing - to allay solvency fears.

Two lawyers for the defence said Bommensath was among around 100‎ recipients of emails sent by Peter Johnson, a former U.S. dollar Libor submitter at Barclays, who is not on trial.

An email from Johnson on Aug. 31, 2007 was read out to the jury and shown on screens in the courtroom. In the email, which was copied to Bommensath, Johnson said: "Fun and games in Libor land ... Just for your guidance, I do not think I am setting Libors high enough!"

In another email, dated Nov. 28, 2007, read out by defence lawyers and shown on screens, Johnson wrote: "Libors are not reflecting the true cost of money... but it is not a good idea at the moment to be seen to be too far away from the pack."

When asked by the defence lawyers to confirm that this was evidence of Barclays setting dollar Libor rates lower than they should have been, Bommensath said money markets were dysfunctional‎ at the time and that he had been focused on dealing with the mortgage crises and credit risk in New York.

He had not been aware that the bank had set inaccurate rates, he said.

Defence lawyers and Barclays have declined to comment.

(Editing by Alexander Smith and Jane Merriman)

By Anjuli Davies and Kirstin Ridley