Those trading with Barclays would have felt cheated if they had got wind of what the five accused bankers had allegedly done, said the lawyer for the fraud squad today.
Former Barclays traders Stylianos Contogoulas, Jay Merchant, Alex Pabon and Ryan Reich, along with one of Barclays' former Libor submitters Jonathan Mathew, have been charged with conspiracy to defraud on allegations of conspiring to manipulate US-dollar linked Libor between June 2005 and September 2007.
Giving his opening speech for the prosecutor the Serious Fraud Office (SFO), James Hines QC produced evidence of emails that showed the traders on trial asking the Libor submitters in London to set the rate to better suit their trading position.
"We ask you to imagine how they [those trading with Barclays] would feel if they read some of the emails," said Hines, before adding: "They would have little difficulty in describing the practice as dishonest."
During the timeframe being assessed in this case, Libor was set by asking submitters from a panel of 16 well-known banks at what rate they could borrow funds by using interbank offers just prior to 11am London time.
Hines added that the counterparties to Barclays' deals were unlikely to have looked for any sort of confirmation that the rate was not rigged because "some things are so fundamental that they hardly need saying".
Hines added: "They were entitled to assume that it was a given that they were dealing with Barclays fair and square."
Describing the defendants as "intelligent", Hines remarked that they could have also betrayed their employer's trust through their alleged actions.
"These men were trusted by Barclays Bank to trade in deal worth billions of dollars," Hines said.
The trial is the third case the SFO has brought to trial in relation to its ongoing Libor investigation, which started in 2012.
The case is currently being heard at Southwark Crown Court and is expected to last for 12 weeks.