These are the questions that Sir Keir Starmer could have been confronted with if MPs had voted for him to face a Privileges Committee investigation:

1. How can he insist there was no pressure for the Foreign Office to process Peter Mandelson's security clearance when senior civil servants say there was?

The Prime Minister assured MPs last week that 'no pressure existed whatsoever in relation to this case', but three senior Whitehall officials have told the foreign affairs committee that there was, although they insist it did not affect their decisions.

2. Does he accept he misquoted the mandarin he sacked over the scandal?

Sir Keir said ousted Foreign Office chief Sir Olly Robbins had said his vetting decision was 'rigorously independent of any pressure' but in fact he said the decision was 'rigorously independent of that pressure'.

3. How can he claim due process was followed when the evidence shows that it was not?

Sir Keir said last week he still believed 'full due process was followed'. Yet former Foreign Office chief Sir Philip Barton on Tuesday declined to agree with his assessment and pointed out that it was unusual for Mandelson's appointment to be announced before vetting had taken place.

4. Why is there no record of him deciding to appoint Mandelson as ambassador?

In another twist to the saga, it emerged on Tuesday that the Government cannot find any minutes of the fateful meeting in December 2024 when Sir Keir decided to give the New Labour grandee the prestigious posting to Washington DC.

5. Why did Sir Keir ignore advice to carry out vetting before announcing the appointment?

The Prime Minister was told by the then head of the civil service, Simon Case, that background checks should be carried out before a political appointment is confirmed – but this did not happen.

6. Who leaked the vetting file?

A leak inquiry was set up after the secret details of Mandelson's security checks were published by the Guardian. Almost two weeks later, it is unclear what progress has been made.

7. Should the leaker be prosecuted?

Sir Olly told MPs he wanted prosecutions for the 'grievous breach of national security', but asked if she agreed, Cabinet Office chief Cat Little would say only: 'I will not comment on other people's judgment.'

8. Does he now accept that Sir Olly did not overrule UK Security Vetting?

The Government claimed Sir Olly had granted Mandelson developed vetting clearance 'against the recommendation' of experts. It has since emerged that those involved described it as a 'borderline' case.

9. Does he still think he was right to sack Sir Olly?

The previous Foreign Office chief Sir Philip said the usual process when civil servants are accused of serious wrongdoing would be to suspend them.

10. Did he even give Sir Olly a chance to explain himself?

The ousted mandarin said he regretted that the claims being made by Sir Keir 'were not put to me before I received a letter dismissing me'.