LONDON, April 16 (Reuters) - Peter Mandelson, the former British ambassador to Washington who was fired for his links to Jeffrey Epstein, failed his security vetting before taking up the role but foreign ministry officials overruled the advice, the Guardian reported on Thursday.

The report increases pressure on Prime Minister Keir Starmer over his appointment of Mandelson, who is under police investigation for allegedly leaking government documents to the late sex offender, and led to renewed calls for him to resign.

Starmer has apologised for the appointment but defended his own actions, accusing Mandelson of creating a "litany of deceit" about his Epstein ties and promising to release documents on how he was appointed.

However, the Guardian reported that Mandelson had failed his security vetting for the role, citing multiple unnamed sources, before officials at the foreign office intervened to override the recommendation and let Mandelson take up the post.

MANDELSON FIRED IN SEPTEMBER

The Guardian reported that the failed security check came after Mandelson's appointment had been announced. The government has previously pledged to overhaul the vetting process and "address weaknesses" in the system.

Mandelson has not commented publicly on allegations he leaked documents, and a lawyer for Mandelson did not provide a comment about the report.

Starmer's Downing Street Office and the Foreign Office did not have an immediate comment on the report, which also said that officials were considering whether to withhold publication of the documents that would reveal Mandelson had not been given security clearance.

Mandelson, 72, was fired from the most prestigious posting in Britain's diplomatic service in September, when the depth of his friendship with the convicted sex offender started to become clear.

His relationship with Epstein, who died in prison while awaiting trial in 2019 on sex trafficking charges, is at the centre of a British political scandal that has forced the resignation of two senior government officials.

OPPOSITION PARTIES SAY STARMER MISLED PARLIAMENT

The opposition leader Kemi Badenoch accused Starmer of misleading parliament when he said three times in September that "full due process" was followed.

If Starmer was found to have knowingly misled parliament, he would have broken the code that governs ministers' behaviour and would be expected to resign.

"Keir Starmer said in February that the security services had given Mandelson 'clearance for the role'," said Nigel Farage, leader of the populist Reform UK Party which is leading polls. "Now we discover that he has blatantly lied, the prime minister should resign."

Mandelson was arrested in February on suspicion of misconduct in public office after Starmer's government passed on communications between the former ambassador and Epstein. He was later released on bail, pending further investigation.

Starmer faces further scrutiny as parliament is expected to release more documents related to his vetting.

Former Prime Minister Boris Johnson was forced to resign in 2022 in part because of months of embarrassing headlines about illicit parties held in government buildings during the COVID pandemic and accusations he misled parliament.

(Reporting by Alistair Smout and Andrew MacAskill; Editing by Alison Williams)

By Alistair Smout and Andrew MacAskill