The Serious Fraud Office (SFO) said a court order restricting publicity of the guilty plea had been lifted five weeks into the London trial of five other former Barclays bankers on Libor rigging charges.

Johnson's guilty plea, the first in a Libor-related case in Britain, was not publishable before because of concerns by a judge handling the case at the time that it might prejudice the trial of the co-defendants.

Johnson's lawyer declined to comment.

Johnson, 61, was charged alongside his former colleagues Jonathan Mathew, Stylianos Contogoulas, Jay Merchant, Alex Pabon and Ryan Reich, who are on trial at Southwark Crown Court.

The five defendants have each pleaded not guilty to one charge of conspiracy to defraud by manipulating Libor between 2005 and 2007. It is the third trial of individuals accused of rigging the ‎London interbank offered rate, a benchmark for trillions of dollars of financial contracts and household loans.

The SFO alleges the five men were dishonest when they submitted or asked colleagues to submit Libor rates - designed to be an independent assessment of a bank's borrowing costs - to benefit trading positions.

A handful of bankers have pleaded guilty in the United States to fraud offences linked to alleged Libor manipulation. Takayuki Yagami, a former Rabobank trader, became the first person worldwide to admit guilt when he pleaded guilty in the United States in June 2014. Yagami is not scheduled to be sentenced until June 2017.

(Reporting by Kirstin Ridley. Editing by Jane Merriman)

By Kirstin Ridley