Britain’s prime minister is confronting a deepening political crisis after his chief of staff resigned amid controversy over the appointment of a former senior politician as the United Kingdom’s ambassador to the United States despite that figure’s documented association with convicted sex offender Jeffrey Epstein.

Morgan McSweeney announced on Sunday that he was stepping down as chief of staff to Prime Minister Keir Starmer, taking full responsibility for having advised the prime minister to appoint Peter Mandelson, 72, to London’s most important diplomatic post in late 2024. McSweeney said in a statement that the decision had damaged trust in politics and eroded public confidence in both the governing party and the wider system.

The controversy stems from newly published files linked to U.S. government documents and private correspondence that revealed a long-standing relationship between Mandelson and Epstein that continued after Epstein’s 2008 conviction for soliciting a minor.

The disclosures included emails suggesting that Mandelson shared sensitive information and maintained close communications with Epstein while serving in government, as well as reports of payments linked to Epstein, intensifying scrutiny of both the former ambassador and the vetting process that led to his appointment.

Starmer, who has publicly acknowledged that he regretted appointing Mandelson and has pledged to release relevant internal correspondence to show that Mandelson misled officials during vetting, faces mounting pressure as critics across the political spectrum question his judgement.

Opposition leaders have called for accountability and, in some cases, suggested the prime minister should consider his own position in office.

McSweeney’s departure — a key architect of the prime minister’s 2024 election victory and a central figure within Downing Street — marks a significant shake-up at the heart of government.

Mandelson, a veteran Labour Party politician who was dismissed from the ambassadorial post in September 2025, has denied wrongdoing but remains under investigation by metropolitan police for alleged misconduct in public office connected to the revelations.

While he has not been charged with sexual offences, the high-profile investigation continues, and Mandelson recently resigned his membership of the Labour Party and the House of Lords amid the fallout.

In his resignation statement, McSweeney acknowledged his long-term commitment to the government’s mission and achievements but said the “honourable course” was to step aside.

Starmer recognised McSweeney’s contribution to the party’s renewal and electoral success, emphasising gratitude for his service even as the administration works to repair trust and address the institutional implications of the scandal.

The episode has underscored broader questions about vetting processes for senior appointments and the standards of accountability expected of political leadership in Britain.