LONDON — U.K. Prime Minister Keir Starmer resisted demands to resign over revelations that his pick for U.K. ambassador to Washington was appointed despite failing security checks. Starmer said he was not informed that the Foreign Office had overruled the recommendation of security officials in early 2025 not to appoint Peter Mandelson to the post.

Starmer's office said he only found out recently that Mandelson had failed security vetting. Starmer insisted that due process was followed in the appointment, which was announced in December 2024. Mandelson, a former European Union trade chief, took up the Washington post in February 2025 after undergoing security vetting.

Darren Jones, chief secretary to the prime minister, said the Foreign Office ignored the recommendation not to appoint Mandelson and that no government minister had been told of the security assessment. "The recommendation was to not appoint Peter Mandelson to the role," Jones said.

Olly Robbins resigned as the top Foreign Office civil servant over the decision to appoint Mandelson. Documents released by the U.K. government in March showed that Starmer ignored red flags raised by his staff about Mandelson's appointment, according to public records.

Kemi Badenoch, leader of the Conservative Party, rejected the prime minister's account. "This story does not stack up," Badenoch said. "The prime minister is taking us for fools. All roads lead to a resignation."

Ed Davey, leader of the Liberal Democrats, said Starmer must resign if he misled Parliament and lied to the British public. The Liberal Democrats asked the prime minister's ethics adviser to investigate whether Starmer broke the government code of conduct by misleading Parliament.

Mandelson had a past friendship with Jeffrey Epstein, who died in prison in 2019. Starmer led the Labour Party to a landslide election victory in July 2024, before the Mandelson appointment became a source of political pressure for his government in early 2025.