ISC Chair Kevan Jones, a Labour peer, previously told the BBC that the committee would not withhold “embarrassing” revelations that did not jeopardize national security.

In the same BBC interview on Feb. 4, Jones did not fully set out what his position would be on any document deemed to prejudice international relations, saying: “International relations aren’t covered by our committee and if the government are going to give us that information, that’s fine.” But when pressed, he responded: “Let’s see what it is. In the past, for example, we’ve had disputes where things you have potentially been embarrassing to government, but we’ve put them in because it doesn’t jeopardize national security.”

Two of the four people with knowledge of the process quoted above emphasized that the ISC, a cross-party committee of MPs and peers, has not been leaned on, and is judging whether documents prejudice foreign relations of its own volition.

They both stressed that this had been the view of the ISC all along, despite the original revolt by Labour MPs over the scope of the motion.

One Labour MP said: “There was no world in which MPs wanted to publish stuff that would prejudice foreign relations. They just didn’t trust the government, which is a damning indictment in itself.”

Starmer’s government has just over a week to publish the next batch of files relating to Mandelson before parliament ends its current session ahead of high-stakes elections on May 7. If they are not released in time, they will not be published before mid-May.

A Conservative Party spokesman said: “There is absolutely no justification for any further cover-ups. Let sunlight be the disinfectant, everything put in the open, and every document published. Anything less will rightly lead people to conclude there is more deviousness, more obfuscation, and almost certainly just result in the information being revealed later, with even more damaging consequences.”