The Tories are attempting to force the Government to release all documents showing how Lord Mandelson got the Washington job, including messages exchanged with key figures in Sir Keir’s inner circle including chief of staff Morgan McSweeney and top ministers. Speaking during PMQs today, the Prime Minister insisted Lord Mandelson had “lied repeatedly” during the appointment process to the US ambassador role.

The PM, who is already facing mounting questions over his leadership amid Labour’s plummeting poll ratings, said: “Mandelson betrayed our country, our Parliament and my party.

“He lied repeatedly to my team when asked about his relationship with Epstein before and during his tenure as ambassador, I regret appointing him.

“If I knew then what I know now, he would never have been anywhere near government.”

Papers on Lord Mandelson’s appointment as ambassador to the US will be released by the Government after Tory leader Kemi Badenoch used a parliamentary process to demand the documents.

The Prime Minister has agreed to release papers as long as they do not prejudice national security or international relations.

Lord Mandelson has quit the Lords and faces a criminal investigation for alleged misconduct in public office after files released by the US Department of Justice appeared to show internal government information on the response to the global financial crisis in 2009 was sent to Epstein.