British Prime Minister Keir Starmer's chief of staff, Morgan McSweeney, announced his resignation on Sunday for having "advised" the head of government to appoint Peter Mandelson as ambassador to Washington, despite his known links with sex offender Jeffrey Epstein.

"After careful consideration, I have decided to resign from the government. The appointment of Peter Mandelson was a mistake (...) When asked, I advised the Prime Minister to proceed with this appointment and I take full responsibility for that advice," Morgan McSweeney announced in a written statement sent to the BBC.

Keir Starmer's government is plunged into an unprecedented crisis following the latest revelations concerning the links between Peter Mandelson and the American financier, who died in 2019.

While some, even within his own party, were calling for his departure from Downing Street, his chief of staff was particularly under fire for having pushed for Mr. Mandelson's appointment as ambassador to Washington.

Keir Starmer had appointed the former Labour minister and European Commissioner in December 2024 to this highly strategic post with the return of Donald Trump to the White House, but dismissed him in September 2025 after the publication of documents in the Epstein case detailing the extent of his links with the pedophile.

New documents recently published by the US Department of Justice have reignited the controversy, revealing that Mr. Mandelson allegedly passed on information to Jeffrey Epstein that could influence the markets, particularly when he was a minister in Gordon Brown's Labour government between 2008 and 2010.

British police have opened an investigation and on Friday searched two addresses linked to Peter Mandelson, one in southwest England and the other in London.

This week Keir Starmer said he regretted appointing Peter Mandelson and apologized to Epstein's victims, but maintained that he did not know the extent of the links between his former ambassador and the pedophile.

In Downing Street, Morgan McSweeney was considered the strategist of Labour power, the true right-hand man and éminence grise of Keir Starmer.

He was appointed in October 2024, three months after Labour returned to power, having been one of the main architects of which he was chief executive of the parliamentary campaign.