British Prime Minister Keir Starmer’s chief of staff, Morgan McSweeney, resigned on Sunday after taking responsibility for advising Starmer to appoint Peter Mandelson as U.S. ambassador, a decision that has drawn intense scrutiny following disclosures about Mandelson’s ties to Jeffrey Epstein.

After new files revealed the depth of the Labour veteran's relationship with the late sex offender, Starmer is facing what is ‌widely seen as the gravest crisis of his 18 months in power over ‍his decision to send Mandelson to Washington in 2024.

The loss of McSweeney, 48, a strategist who was instrumental in Starmer's rise to power, is the latest in a series of setbacks, less than two years after the Labour Party won one of the largest parliamentary majorities in modern British history.

Starmer in the firing line

With polls showing Starmer is hugely unpopular with voters after a series of embarrassing U-turns, some in his own party are openly questioning his judgment and his future, and it remains to be seen whether McSweeney's exit will be enough to silence critics.

The files released in the U.S. on Jan. 30 sparked a police investigation for misconduct in office over indications that Mandelson leaked market-sensitive information to Epstein when he was a government minister during ⁠the global financial crisis in 2009 and 2010.

In a statement, McSweeney said: "The decision to appoint Peter Mandelson was wrong. He has damaged our party, our country and trust in politics itself.

"When asked, I advised the Prime Minister to make that appointment and I take full responsibility for that advice."

The leader of the opposition Conservative Party, Kemi Badenoch, said the resignation was overdue and that "Keir Starmer has to take responsibility for his own terrible decisions".

Nigel Farage, head of the populist Reform UK party, which is leading in the polls, said he believed Starmer's time would soon be up.

Starmer has spent the last week defending McSweeney, a strategy that could prompt further ‌questions about his own judgment. In a statement on Sunday, Starmer said it had been "an honour" working with him.

Ties with Trump

Many Labour members of parliament had blamed McSweeney for the appointment of Mandelson and the damage caused by the publication of the exchanges between Epstein and Mandelson. Others have said Starmer must go.

One Labour lawmaker, speaking on condition of ‍anonymity, said McSweeney's resignation had come too late: "It buys the PM time, but it's still the end of days."

Starmer sacked Mandelson as ambassador in September over his links to Epstein.

The government agreed last week to release ‍virtually all previously private communications between ‍members of his government from the time when Mandelson was being appointed.

That release ⁠could come as early as this week, creating a new headache for ‍Starmer just as he hopes to move on. If previously secret messages about how London planned to approach its relationship with Donald Trump are made public it could damage Starmer's relationship with the U.S. President.

McSweeney had held the role of chief of staff since October 2024, when he was handed the job following the resignation of Sue Gray after a row over pay ⁠and donations.

It was unclear ‌who would replace McSweeney. Vidhya Alakeson, who worked closely with Starmer in opposition, is the prime minister's deputy chief of staff.