U.K. Prime Minister Keir Starmer’s chief of staff, Morgan McSweeney, has resigned from government following the revelations about Peter Mandelson in the Epstein files.

Documents released by the U.S. administration revealed that Starmer’s former ambassador to Washington D.C. remained in contact with the convicted sex offender longer than he initially admitted. Police are also investigating emails that appear to show Mandelson forwarding the details of internal financial discussions to Epstein after the 2008 banking crash.

The decision means Starmer has lost one of his most loyal and long-serving lieutenants when he is already under intense pressure from his own MPs and party, with some privately calling for the prime minister to resign.

In a statement issued on Sunday afternoon, McSweeney said that the decision to appoint Mandelson was “wrong” and “ damaged our party, our country and trust in politics itself.”

He said he took “full responsibility” after personally advising Starmer to make the appointment. He added: “In public life responsibility must be owned when it matters most, not just when it is most convenient. In the circumstances, the only honourable course is to step aside.”

McSweeney has been a key aide to Starmer throughout his time as Labour Party leader. His work behind the scenes in the late 2010s, first at the Labour Together think tank and then for Starmer himself, helped rout the party’s left flank and propel Starmer to the leadership and then Downing Street.

However, McSweeney had long been under pressure to resign. This escalated after the U.S. Department of Justice published further emails showing the extent of the relationship between Peter Mandelson — the former U.K. ambassador to the United States — and the late financier and sex offender Jeffrey Epstein.

Mandelson was appointed to the role in December 2024, but was sacked in September last year after further details of his relationship with Epstein were made public. Following the publication of further emails earlier this month, Mandelson resigned his Labour Party membership and place in the House of Lords.

Both Starmer and McSweeney have been under intense pressure for backing Mandelson’s appointment, with Labour MPs and former cabinet ministers calling both to consider their futures.

This is a developing story and will be updated.