British Prime Minister Keir Starmer has suffered a major political blow following the resignation of his chief of staff, Morgan McSweeney, amid mounting fallout over the controversial appointment of Peter Mandelson as the UK ambassador to the United States.

McSweeney announced his resignation on Sunday, admitting that recommending Mandelson for the high-profile diplomatic role was a “wrong” decision and taking full responsibility for advising the prime minister. The resignation comes after renewed scrutiny of Mandelson’s past links to convicted sex offender Jeffrey Epstein, following the release of emails by the US Justice Department.

The controversy has reignited criticism of Starmer’s judgment, with opposition figures and members of his own party questioning why Mandelson was considered for the role despite longstanding concerns. Starmer had previously removed Mandelson from the ambassadorial post in September after earlier revelations about his ties to Epstein, making the latest developments particularly damaging.

Critics argue that the episode has undermined trust in the prime minister’s leadership and decision-making at a sensitive time for the government. While Downing Street has sought to limit the political fallout, the resignation of such a senior aide has intensified pressure on Starmer, with some lawmakers warning the scandal could have longer-term consequences for his premiership.