Foreign Office mandarin Sir Olly Robbins was sacked last night following the latest Peter Mandelson scandal.

Sir Keir Starmer denied that he or any of his ministers had been aware that Mandelson, the controversial architect of New Labour, had failed his developed vetting (DV) for the US ambassador role, only for the Foreign Office to overrule the decision.

The Downing Street denial, which was under severe scrutiny last night, raises questions about who took the decision to force the appointment through, regardless of the red flags.

As the most senior civil servant at the Foreign Office at the time, Sir Olly was firmly in the frame. Fears he was being lined up as the fall guy were confirmed last night.

The Daily Mail understands the PM and Foreign Secretary Yvette Cooper had lost confidence in Sir Olly, who joined the Treasury in 1996.

In 2006, Tony Blair made him his principal private secretary, and he moved to the Cabinet Office under Gordon Brown. He served as David Cameron's deputy national security adviser and worked in the Home Office when Theresa May was home secretary, eventually becoming her chief Brexit official.

He was accused of having too much sway over Mrs May, and was described as 'the most powerful man in Westminster that you've never heard of'. In a rare public intervention, then Cabinet secretary Mark Sedwill said critics of Sir Olly 'should be ashamed of themselves'.

In September 2018, Sir Olly refused to say whether he believed leaving the EU would be a 'good thing'. Ultimately, he was accused of giving away too much to Brussels in his failed negotiations.

Sir Keir announced Mandelson as the UK's man in Washington in December 2024. No 10 ignored warnings about the peer's friendship with paedophile Jeffrey Epstein, while 'senior figures' in the Foreign Office were said to have 'advised against' giving the role to someone who was twice forced to resign from Cabinet.

The following month, Sir Olly was appointed Foreign Office permanent secretary, assisting then foreign secretary David Lammy.

Remarkably, it was only after he had been publicly given the job that Mandelson, Labour's self-confessed Prince of Darkness, faced vetting for it. And it emerged yesterday that the UK Security Vetting (UKSV), a division of the Cabinet Office that scrutinises the background of prospective civil servants, turned him down.

Faced with a dilemma - given that his appointment had been announced - officials at the Foreign Office invoked rarely used powers to override the recommendation.

Following Mandelson's sacking in September last year - over fresh information about his links to Epstein - the department concealed the failure.

Sir Olly signed off on Lord Mandelson's £75,000 payout after he resigned, arguing it was 'good value for money'.

Ms Cooper, by now Foreign Secretary, and Sir Olly wrote to the foreign affairs committee to say the security vetting was conducted 'to the usual standard'. They added that this had 'concluded with DV clearance being granted by the FCDO'.

It did not mention that the UKSV had denied him clearance. It is not known why Mandelson failed the checks, but the process involves the disclosure of personal information, including financial and sexual history. 

Following the peer's departure, Sir Olly was also questioned at a foreign affairs select committee and again failed to disclose the vetting debacle.

Last night, before Sir Olly was sacked, Labour grandee Emily Thornberry, the committee chairman, said she would haul the mandarin back to answer questions. 

'Looking at the evidence that was given and the letters that have been written, to be charitable, there are glaring holes,' she said.

During the hearing, Sir Olly said the 'vast majority' of vetting reports were 'relatively straightforward'. 

He added: 'Ones that require more senior judgment, and potentially a discussion about managing and mitigating risks, are escalated appropriately.'

Sir Chris Wormald, who was at the time Cabinet secretary, also gave evidence. He said the developed vetting process would typically culminate in a report that was received by a 'line manager - in this case, that would be Sir Oliver - and a decision is taken on whether the relevant level of security clearance is to be granted and what mitigations, if any, are required'.

There were also concerns last night about why the vetting scandal had not yet been released in documents relating to the case.

It was not contained in a tranche of 147 pages of documents on Mandelson's appointment released last month after the Conservatives backed the Government into a corner. Tory leader Kemi Badenoch said: 'It looks like there's been a cover-up, because we had a Humble Address in Parliament where we asked for all of the documents. This did not come out then.'

Cover-up fears were last night stoked by reports that senior government officials had been considering whether to withhold the vetting failure documents from Parliament, according to The Guardian.