Fiddling with his reading glasses, the then cabinet secretary, Sir Chris Wormald – sitting alongside the most senior civil servant in the Foreign Office, Sir Olly Robbins – suddenly appeared a little tense.

The bonhomie evident in earlier answers had quite disappeared.

It was 3 November 2025, and Peter Mandelson had been removed from his post as ambassador to the US two months earlier, after the disclosure of Jeffrey Epstein’s emails.

MPs on the cross-party foreign affairs select committee were grilling the most senior civil servants involved in Mandelson’s appointment about the vetting and due diligence.

Just over an hour in, Fleur Anderson, the MP for Putney, asked what can now be seen as a crucial question about the process: “In general, what is the end product of all that vetting? Does it all get put into one report? Who receives that report?”

“The report is received by the employing department and employing line manager – in this case, that would be Sir Oliver,” Wormald responded, looking to his left towards Robbins. “And then a decision is taken on whether the relevant level of security clearance is to be granted and what mitigations, if any, are required.”

Anderson wanted to know a little more. Was Wormald himself made aware of what the security services had said?

For whatever reason, Robbins sought to interject with an answer to quite a different question.

“May I cut in, Chris?” Robbins said, before informing the committee that it was not normally the case that decisions would be made at his level, only those “that require more senior judgment, and potentially a discussion about managing and mitigating risks”.

The committee never did discover what Wormald knew. He was removed from his job as the country’s highest civil servant in February this year.

The Guardian’s revelation that Robbins had cleared Mandelson’s appointment despite him failing his security vetting has electrified the question of who knew what and when.

Speaking on Friday, Keir Starmer emphasised that the politicians had been left in the dark. “That I wasn’t told that he’d failed security vetting when I was telling parliament that due process had been followed is unforgivable,” he told the broadcasters. “Not only was I not told, no minister was told and I’m absolutely furious about it.”

Those who have worked in Downing Street find it hard to believe that Robbins did not seek some cover for his decision to overrule the vetting team’s conclusion.

“These appointments are usually so careful,” said one. If the prime minister’s word is accepted, and neither he nor the then foreign secretary, David Lammy, knew, could it really be the case that Wormald was not let in on the secret?

Friends of Robbins have also sought to defend him from claims that he somehow acted improperly.

It was not a matter of overruling the United Kingdom Security Vetting service, they said, but as permanent secretary, Robbins was the last part of the process. The most difficult issue, Robbins had told the select committee, was ensuring there were no conflict-of-interest issues between Mandelson’s new role and the consultancy he had founded, Global Counsel. When that was established, Robbins had taken the advice of the security services and made his decision to grant clearance based on the totality of the evidence.

One crucial factor would have been that it was clear, for example, that the prime minister wanted Mandelson in post. The FCDO then “acted on that view”, as Robbins told the select committee.

Civil servants who are not friends of Robbins say they can also understand how it all happened. One said: “I loathe Olly – he is arrogant to colleagues and condescending to ministerial authority – but it isn’t fair for him to be sacked just for doing what the prime minister wanted to happen.”

A more friendly colleague said Robbins had been left in an impossible position. He had only recently been made head of the FCDO. Mandelson’s appointment had already been announced. The vetting was the last bit of paperwork. “Was his first big act really going to be to tell the prime minister that this could not go ahead?” they asked.

Friends of Robbins suggest it was instead a case of politicians simply looking the other way as Mandelson, whose vetting had been fast-tracked for him to be in post, was ushered into the role despite ample evidence of the risks.

Darren Jones MP, the chief secretary to the prime minister, expressed his astonishment during the Friday morning media round that it was even allowed for a permanent secretary to overrule the conclusions of the vetting services without informing ministers.

But even that protestation seems difficult to square with the evidence. In September, soon after Mandelson’s fall, Emily Thornberry, the chair of the foreign affairs select committee, sent a letter to the new foreign secretary, Yvette Cooper.

Thornberry asked what security concerns were raised during the vetting process and what the response of the FCDO had been. Were any conditions imposed on Mandelson as a result? Was there a decision to dismiss security concerns?

The response was a dead bat. Cooper wrote back jointly with Robbins: “We do not comment on the details of individual clearances or national security as a matter of course.

“The UK government’s national security vetting charter includes an undertaking to protect personal data and other information in the strictest confidence … The process is also independent of ministers who are not informed of any findings other than the final outcome. This remained the case in this instance.”

In response to Thornberry’s question as to whether security concerns had been dismissed and if it was the FCDO or No 10 who made the decision to disregard those concerns, Cooper and Robbins responded: “It is not a process which involves No 10.”

If this letter is taken at face value, the foreign secretary accepted that only Robbins knew whether concerns had been raised, and what mitigation had been put in place, and she had simply accepted that it was not for her or Downing Street to pry.

Meanwhile, the prime minister was telling parliament that due process had been carried out and claiming in media interviews that an independent vetting process involving the security services had given Mandelson “clearance for this role”.

“I think Olly has been treated appallingly,” said a friend. “He has been deputy national security adviser, director of intelligence and security; it is not as if he doesn’t know his stuff.” They added: “This is just the death throes of a prime minister desperately trying to stay in his job.”