Three former Barclays bankers have been charged in relation to allegations of a conspiracy to manipulate Libor interest rates.

The Serious Fraud Office said the men were charged in connection with an allegation of conspiracy to defraud between 1 June 2005 and 31 August 2007.

The bank was fined £290m by US and UK regulators two years ago for a "serious, widespread" role in trying to manipulate Libor rates. There was no admission of criminal liability but the scandal ultimately led to the departure of the chief executive, Bob Diamond.

Although Barclays was the first of several banks to reach a regulatory settlement of Libor allegations, neither existing nor former employees had been named in criminal proceedings until Monday.

The focus of criminal proceedings until now has been a former Citigroup and UBS trader, Tom Hayes, who is charged with conspiracy to fix Libor with employees at eight other financial firms including Royal Bank of Scotland, JP Morgan Chase, Deutsche Bank, Icap, Tullett Prebon, Rabobank RP Martin and HSBC.

It is thought that the latest charges brought against former Barclays staff relate to a separate alleged conspiracy, unrelated to the alleged plots between August 2006 and September 2010 involving Hayes.

The three former Barclays bankers are Jonathan Mathew, who worked in the bank's treasury unit in London and left this position in September 2012, Peter Johnson, who is thought to have been a senior dollar Libor submitter in London, and Stylianos Contogoulas, a former trader at Barclays who moved to Merrill Lynch in July 2006 and left there in September 2011.

Barclays declined to comment.