Prosecutors said that Hayes acted as the ringleader in manipulating yen Libor by asking rate setters and traders at UBS and several other banks who were on the panel that set the daily rate, and external brokers, to move the rate up or down in order to benefit his trading positions. Even minor movements in the rate can result in bumper profits for a trader manipulating the rates.

In addition, Hayes rewarded the brokers who helped him influence other banks to move the rate, by paying them extra commission through wash trades, a system prosecutors said amounted to paying bribes.

During the trial, the court heard that manipulating Libor rates was so commonplace that an offer of a Mars bar could get it changed. Hayes told a fellow trader: "Just give the cash desk a Mars bar and they'll set wherever you want."

Hayes confessed, saying that he did not want to be extradited to the US.

He claimed that the manipulation was widespread.