For more than a year, ministers and officials defended Peter Mandelson’s appointment to Washington with a simple account: he had been vetted, and Developed Vetting clearance had been granted. Evidence now before Parliament shows that version left out the most consequential stage in the process: the government’s own security vetting body had recommended that the clearance be denied before the Foreign Office granted it anyway.

That omission, rather than the narrower question of whether Mandelson was ever vetted at all, has become the centre of a widening constitutional dispute at Westminster. The Foreign, Commonwealth and Development Office had the formal authority, under the system then in place, to make the final decision on Developed Vetting. But the issue now confronting No. 10 is whether ministers, the Cabinet Office and Parliament were given a materially incomplete account — one that conveyed only the endpoint, “clearance granted”, while omitting the decisive intermediate fact that UK Security Vetting had recommended refusal.

Sir Keir Starmer told the Commons on 20 April that he first learned on 14 April this year that FCDO officials had granted clearance against UKSV’s recommendation. He said that, had he known before Mandelson took up post, “I would not have gone ahead with the appointment.” That statement is politically damaging in its own right. It means the Prime Minister is now saying that the information withheld from him was not incidental but determinative.

Nothing disclosed so far proves that Starmer knowingly misled Parliament when he told MPs on 10 September 2025 that “full due process was followed”. But the documentary trail and committee evidence now in public point to a more precisely provable problem: Parliament was given a narrower account than the one held within the system.

The chronology is now unusually clear. Mandelson answered No. 10 due diligence questions on 11 December 2024. Starmer received final due diligence advice the following day and decided on 18 December to appoint him. The appointment was announced publicly on 20 December. Only then, on 23 December, did the Developed Vetting process begin.

That sequence matters because it shows the political decision predated the security judgment. The government has argued that this was not exceptional under the arrangements operating at the time, with external appointments sometimes announced before all clearance processes were complete. But it also meant the state’s vetting machinery was assessing a candidate whose appointment had already been publicly committed to.

According to Starmer’s Commons statement, UKSV conducted the vetting in the normal way, including two interviews, and on 28 January 2025 recommended that Developed Vetting be denied. On 29 January, the FCDO granted the clearance anyway. Starmer told MPs that, unlike in many other departments where UKSV’s decision is binding, the FCDO was then the final decision-maker. Cat Little, the Cabinet Office permanent secretary, gave MPs a similar account this week, describing the FCDO as a “make recommendation” department in which UKSV’s recommendation was not binding.

That is an important distinction. It means the case is not, at least on the evidence now available, that the system broke down in a formal sense. The process existed. UKSV did its work. The FCDO made the final call available to it under the rules then in force. If the story ended there, ministers could plausibly argue that due process had in fact been followed.

But the public and parliamentary account did not end there. It moved into more dangerous territory in September 2025, when questions about Mandelson’s appointment intensified.

At Prime Minister’s Questions on 10 September, Starmer twice used the formula that “full due process was followed” or had been “gone through”. On 16 September, Yvette Cooper and Sir Olly Robbins wrote to the Foreign Affairs Committee that the vetting process had “concluded with DV clearance being granted by the FCDO” and that ministers had been informed only of the “final outcome”.

Those statements can be defended in a narrow procedural sense. The process did conclude with a grant. Ministers were, apparently, told the outcome that the system had reached. But neither formulation disclosed that UKSV had first recommended denial. In retrospect, that missing fact is exactly what gives the September account its disputed character. “Clearance granted” and “vetted and cleared” do not carry the same meaning, in ordinary parliamentary language, as “clearance granted after the professional vetting body advised refusal”.

Starmer’s later account makes the gap starker still. In his 20 April statement, he said the Cabinet Secretary’s September 2025 review concluded that appropriate processes had been followed, but that the Cabinet Secretary had not been told about the UKSV recommendation to deny clearance. He also said the Foreign Secretary had not been told. If that is correct, the review that underpinned the government’s September defence was incomplete at source.

This is where the case becomes constitutional rather than merely administrative. The Ministerial Code requires ministers to give accurate and truthful information to Parliament and to correct inadvertent errors at the earliest opportunity. The Civil Service Code requires officials to keep accurate records and not knowingly mislead ministers or Parliament. The live questions are therefore no longer abstract. What did Starmer personally know? What did No. 10 institutionally know? Who decided that the “final outcome” was enough? And at what point did the government become obliged to correct the record?

The route by which the missing fact emerged is also significant. On 4 February this year, the Commons agreed a Humble Address requiring the release of papers relating to Mandelson’s appointment, including due diligence material, UKSV-related documents, communications involving Morgan McSweeney, and information given to Starmer before his September assurance to MPs. Little told the Foreign Affairs Committee that she became aware on 25 March, when she read the UKSV summary herself, that the document contained a recommendation to deny clearance. She said the summary was about 10 pages long.

Little did not brief Starmer until 14 April. Her evidence is that she took legal, security, propriety and criminal-investigation advice before doing so because the material was unusually sensitive. That three-week gap has now become a story in itself. It is one thing to argue that detailed vetting material cannot be widely circulated. It is another to explain why the narrow fact that UKSV recommended denial could not have been conveyed earlier to the Prime Minister, particularly when he had already made parliamentary statements resting on the contrary implication.

Documents published by No. 10 after Starmer was told further narrowed the available defence. The government’s own account states that while the detailed contents of vetting files are highly sensitive, there was no legal barrier to officials informing ministers of UKSV’s recommendation or of high-level risks without disclosing sensitive particulars. That is a damaging clarification. It shifts the argument away from “they could not say” and towards “they did not say”.

Robbins’ evidence to MPs on 21 April opened another line of inquiry. He said No. 10 exerted “constant pressure” over Mandelson’s arrival in Washington and was interested in “when”, not “whether”, he would take up post. He also said he was orally briefed that Mandelson was a “borderline” case and that UKSV was leaning towards denial. He did not present himself as someone who had personally studied the underlying written summary before the clearance decision was made.

Little’s evidence two days later sharpened the contradiction. She confirmed that the written UKSV summary included the recommendation and said she could not speak to what Robbins had been told orally. That leaves three broad possibilities: Robbins was inaccurately briefed about the written recommendation, he misunderstood the position, or his later description softened what the document in fact said. Each possibility matters because Robbins was the senior FCDO official at the centre of the 29 January clearance decision and because he did not pass the adverse recommendation to ministers or No. 10.

He has defended that non-disclosure, in part, on grounds of vetting confidentiality and personal responsibility. But that explanation now sits uneasily beside the government’s own acknowledgement that the top-line fact of a denial recommendation could have been shared without exposing sensitive details. It also sits uneasily beside the civil service requirement to keep an accurate record of significant decisions. Among the documents MPs are now seeking are the UKSV summary itself, the 29 January FCDO decision record, secure portal access logs showing who saw the material, and the briefing pack used before Starmer’s September answers in the Commons.

The row is also widening beyond individual knowledge to institutional notice. Starmer says he first learned of the recommendation on 14 April 2026 and that no minister had been told before then. No. 10 has also said it does not accept that media enquiries in September 2025 were equivalent to being told that UKSV had recommended denial. Even so, the presence of public and media scrutiny last autumn, combined with the Cabinet Secretary’s review and the FCDO’s carefully limited language about the “final outcome”, raises an obvious question: why did nobody at the centre of government ask the sharper question sooner — not whether clearance had been granted, but whether UKSV had recommended it?

That question now extends to the political atmosphere surrounding the appointment. Robbins’ description of persistent chasing from No. 10 has intensified scrutiny of McSweeney, Starmer’s former chief of staff, who has denied bullying civil servants and said he does not recognise the picture drawn of him. He is due to appear before MPs next week. His evidence will matter because the pressure line is not simply about tone. Parliament is trying to establish whether a politically favoured appointment was pushed through a compressed timetable in a way that made professional refusal harder, or whether officials acted entirely independently and later failed only in how they described what had happened.

The unanswered questions are now concrete. What did Mandelson disclose in his 10 December due diligence answers? What advice reached Starmer on 11 December before he made the appointment? Is there a formal record of the Prime Minister’s 18 December decision? What precisely did the UKSV summary say on 28 January, and who in the FCDO read it? Who drafted the clearance decision on 29 January? What was in the September 2025 briefing prepared for PMQs? And why did the government’s internal reviews ask whether process had been followed, rather than whether an adverse security recommendation had been overridden?

Those questions are why this story has moved beyond one appointment and into the machinery of government itself. The evidence already supports a narrower but more troubling conclusion than the crudest political charge. Mandelson was vetted. The FCDO did lawfully grant clearance under the process then in force. But Whitehall repeatedly passed upwards the safest fact — clearance granted — while failing to pass upwards the decisive one — that UKSV had recommended denial. Whether that happened through caution, culture, pressure or design is now the point Parliament is trying to settle.