Sir Keir Starmer did not know that Lord Mandelson had been granted top-level security clearance against official vetting advice until earlier this week, the government said on Thursday, after fresh disclosures intensified claims that the prime minister misled Parliament over the former ambassador’s appointment.

Downing Street said the decision to grant Developed Vetting to Mandelson, despite a recommendation against doing so from UK Security Vetting, was taken by officials in the Foreign, Commonwealth and Development Office. It said neither Starmer nor any other minister was told at the time that the clearance had been approved against that advice.

The disclosure follows a report in the Guardian that Mandelson was initially denied security clearance in late January 2025 and that the decision was reversed by the Foreign Office so he could take up the post as Britain’s ambassador to the United States.

A government spokesperson said: “The decision to grant Developed Vetting to Peter Mandelson against the recommendation of UK Security Vetting was taken by officials in the FCDO.

“Neither the prime minister, nor any government minister, was aware that Peter Mandelson was granted Developed Vetting against the advice of UK Security Vetting until earlier this week.

“Once the prime minister was informed he immediately instructed officials to establish the facts about why the Developed Vetting was granted, in order to enact plans to update the House of Commons.”

The admission has added to pressure on Starmer, who has faced repeated questions over comments he made in Parliament and in public defending Mandelson’s appointment.

At Prime Minister’s Questions on 10 September 2025, Starmer said three times that “full due process” had been followed during the appointment. At a press conference in Hastings on 5 February this year, he also said there had been “security vetting carried out independently by the security services” which “gave him clearance for the role”.

Those remarks are now at the centre of the political row. Under the Ministerial Code, ministers must give accurate and truthful information to Parliament and correct any inadvertent error at the earliest opportunity. It also states that ministers who knowingly mislead Parliament are expected to resign.

Conservative leader Kemi Badenoch said Starmer should quit, arguing that Mandelson had been appointed before vetting was complete and had then failed that vetting.

“The prime minister appointed Peter Mandelson before the vetting had been completed, vetting Mandelson failed,” she said. “Starmer then said full due process was followed. That is misleading Parliament.

“I’m only holding him to the same standards to which he’s held previous prime ministers — that if they mislead Parliament, they should resign.”

The Liberal Democrats had already said Starmer should resign if he had misled Parliament. Reform UK, the Green Party and Plaid Cymru have also called for him to go, while the Scottish National Party has written to the independent adviser on ministerial standards, Sir Laurie Magnus, seeking an investigation into whether the prime minister deliberately misled the Commons and the public.

In March, Magnus said that on the documentation then available he could see no grounds to open a ministerial code investigation into Starmer. That assessment, however, pre-dated the disclosure that Mandelson’s clearance had been granted against UK Security Vetting advice.

Mandelson was announced as the UK’s ambassador to the US in December 2024, before enhanced national security checks had been completed, and formally took up the post on 10 February 2025.

He was later sacked as ambassador in September 2025 after renewed scrutiny of his links to the late convicted sex offender Jeffrey Epstein. The appointment has dogged Starmer’s premiership ever since, raising questions over what checks were carried out, what warnings were received and what the prime minister knew when he defended Mandelson in the Commons.

The developed vetting process is carried out by UK Security Vetting, a specialist agency within the Cabinet Office. It is designed to assess whether a person can be trusted with highly classified information and whether they may be vulnerable to blackmail or bribery. The process includes checks on credit history and criminal records and an in-depth interview covering areas such as health, family circumstances, personal relationships and other potential vulnerabilities.

The government has already published some papers relating to Mandelson’s appointment after MPs voted in February to force disclosure of the documents. Those files included an earlier Cabinet Office due diligence check sent to Starmer on 11 December 2024.

That document, based largely on public material such as media reports, warned that Mandelson’s relationship with Epstein posed a “reputation risk”. It did not amount to the full national security vetting later carried out by UK Security Vetting.

Ministers have also already conceded that the process used in the appointment “fell short of what is required”. In March, the government said it would change the rules so that future diplomatic appointments would not be announced until security vetting had been completed.

That change has fuelled opposition claims that Starmer’s earlier insistence that “full due process” had been followed gave MPs a more reassuring picture than the one now emerging from official documents and government statements.

The Guardian also reported that senior officials had considered whether to withhold from Parliament documents showing that Mandelson had not received approval from security vetting officials. The government said on Thursday that it remained committed to complying with the parliamentary motion requiring the release of papers “in full as soon as possible”.

It said any documents requiring redaction on national security or international relations grounds would be provided to Parliament’s Intelligence and Security Committee, which has been asked to review material and determine what can be published. That, the government said, would include papers supplied to the FCDO by UK Security Vetting.

The BBC reported that Mandelson himself had not been told of the negative judgments made during the vetting process and only learned of them when the Guardian story was published. According to that account, no one at any level raised concerns with him after his vetting interview.

The former ambassador is also under separate scrutiny in a Metropolitan Police investigation. Mandelson was arrested on suspicion of misconduct in public office on 23 February over allegations that, while serving as a minister in 2010, he passed market-sensitive government information to Epstein. He was released on bail and his bail conditions were later lifted.

The BBC has reported that Mandelson’s position is that he has not acted in any criminal way and was not motivated by financial gain.

Downing Street now faces renewed demands to explain exactly who in the Foreign Office overruled UK Security Vetting, what information was passed to ministers at the time and whether Starmer will make a formal correction to the Commons.

For now, the government’s defence rests on a narrow but politically significant distinction: that while Starmer’s earlier assurances are under fierce attack, he did not know the most serious fact now in dispute — that Mandelson’s Developed Vetting had been granted against the recommendation of the government’s own vetting agency.