Senior government officials have been considering whether to withhold from parliament sensitive documents that show Peter Mandelson failed security vetting before he assumed the role of US ambassador, the Guardian can reveal.

Any such decision could amount to an extraordinary breach of a parliamentary vote, known as a humble address, that ordered the release of “all papers” relevant to Mandelson’s appointment.

The Guardian has revealed that Mandelson did not receive vetting clearance from security officials, but that their decision was overruled by the Foreign Office to ensure he could take up his post.

According to multiple sources, officials across government have been in dispute over whether to release documents that would reveal those facts, and other information about Mandelson’s security vetting, to the parliamentary intelligence and security committee (ISC).

The committee has been entrusted by parliament with the role of assessing the most sensitive papers relating to Mandelson’s appointment. Ministers have assured parliament that there will be no block on what the committee gets to see.

However, as of Thursday morning, a decision had not been made about whether the committee should have access to documents about Mandelson’s vetting by UK Security Vetting (UKSV) and the decision by the Foreign, Commonwealth and Development Office (FCDO) to override it.

The ultimate decision will rest with the Cabinet Office. But sources said officials were split over how to proceed, with some arguing the materials should be withheld, despite a parliamentary motion to release all relevant materials. One source said: “There is no consensus.”

Late on Thursday, after publication of the Guardian’s revelations, Downing Street indicated the documents would be released to the committee.

“The government is committed to complying with the humble address in full as soon as possible,” a government spokesperson said. “Any documentation within the scope of the humble address that requires redaction on the basis of national security or international relations will be provided to the ISC. This will include documents provided to the FCDO by UK Security Vetting.”

Lord Beamish, chair of the ISC, noted the government’s role in providing documents to the committee. But he added: “The committee would take a very dim view if documents relating to the humble address are withheld from the committee, one which I think would be shared by parliament.”

Mandelson was sacked in September 2025 after the extent of his friendship with the convicted sex offender Jeffrey Epstein was revealed, in documents released to the public by the US department of justice.

A second tranche of DoJ documents released in late January 2026 suggested Mandelson had passed market-sensitive information and Downing Street emails to Epstein while serving in Gordon Brown’s government, prompting fresh parliamentary scrutiny of Keir Starmer’s decision to appoint him.

In February 2026, parliament voted for a rare motion brought by the Tories to compel the government to publicly release “all papers relating to Mandelson’s appointment”. The language in the motion, called a humble address, made an exception for papers “prejudicial to UK national security or international relations”, which it said should be provided to the ISC.

The committee comprises nine MPs and peers, including Jeremy Wright, a former attorney general, and Alan West, a retired Royal Navy admiral. Its members are sworn to secrecy under the Official Secrets Act and are given access to highly classified material. Tasked with overseeing the UK intelligence community on parliament’s behalf, they are now likely to demand answers over the precise basis for the UKSV decision.

During the debate on the humble address, Derek Twigg, a member of the ISC, asked a minister, Chris Ward, for assurances there would be “no block whatsoever” on the material provided to the committee. Ward said: “Yes, I can confirm that.”

According to an ISC press notice, the committee met top officials from the Cabinet Office after the humble address and it was agreed that to “fulfil the will of parliament”, it would be for the committee alone to assess material provided to it by the government and decide if it should be published.

However, sources have said officials have been considering a different approach, and wrestling with whether there could be grounds to withhold highly sensitive UKSV vetting documents from the committee entirely, despite the vote.

One source said officials were wary that disclosure of details of an individual’s vetting, even if access was restricted to a trusted group of parliamentarians, would be “unprecedented”. They pointed to strong concerns, including among the security services, about revealing documents.

A second source said officials were grappling with a “live tactical question” over the release, and searching for loopholes that might enable them to withhold documents from the ISC. They said top officials were “looking for ways to comply with the letter of the humble address while potentially bypassing its spirit”.

The second source said some in government were arguing that any disclosure of documents revealing Mandelon’s UKSV vetting had failed, only to be overruled by the Foreign Office, would “reflect poorly on the government’s overall integrity”. Others, they said, had been arguing that “precedent should be set aside” to comply with parliament’s wishes.

Another option under consideration would be to show the redacted documents to a select number of the nine-person committee.

The Guardian’s revelation that Mandelson had failed the developed vetting process is likely to put pressure on the government to release the documents to the public in full.

Details of an individual’s UKSV developed vetting results have never before been publicly disclosed, and some top officials have been arguing that doing so would jeopardise national security.

According to publicly available government documents, the vetting process includes a questionnaire and interviews requiring disclosure of highly private information, including about personal finances, business connections and sexual history. The security services are also consulted.

Regardless of the final decision by the Cabinet Office, the notion that officials have even contemplated whether to withhold the Mandelson vetting documents, in what would appear to be a breach of parliament’s wishes, could prove hugely controversial.

Such a move could raise a constitutional conflict, with officialdom and the security services challenging the supremacy of parliament. It would also raise questions about whether the government is adhering to its word.

In a letter on 6 February 2026 to the chair of the committee, Starmer said: “Above all else, the government wishes to engage constructively with the ISC, and to ensure that parliament’s instruction is met with the urgency and transparency it deserves.”

The Foreign Office, Downing Street and the Cabinet Office have been approached for comment.