The prime minister faces a standards investigation over Mandelson affair and testimony from Morgan McSweeney

Keir Starmer has told Labour MPs to “stick together and fight together” as ministers launched a massive operation to shore up his fragile position before a critical day for his premiership.

The prime minister faces the double threat of a standards investigation into his decision to appoint Peter Mandelson as ambassador to the US and a potentially damaging testimony from Morgan McSweeney, his former chief of staff.

PM to tell Commons he was himself misled and would ‘never knowingly mislead parliament or the public’

• UK politics live – latest updates

Keir Starmer is expected to admit he inadvertently gave MPs misleading information about Peter Mandelson’s vetting when he addresses the Commons.

But his spokesperson said the prime minister would “never knowingly mislead parliament or the public” and that he was himself misled.

Exclusive: deputy PM says UK will not join Iran conflict despite Trump’s sometimes ‘incomprehensible’ social-media barbs

Donald Trump’s insults towards Keir Starmer are “small and petty” and designed to put pressure on the prime minister to change his position on Iran, David Lammy has said, as he insisted the UK would not get dragged into the conflict.

The deputy prime minister argued the US president should be able to “disagree agreeably” with allies rather than publishing attacks on social media, and that US actions had “made things worse, not better” as far as global instability was concerned.

Prime minister to deliver high-stakes statement to MPs over vetting controversy that has put his position in peril

Keir Starmer will deliver a high-stakes statement to MPs on Monday as he struggles to overcome fears inside his government that the Peter Mandelson vetting scandal could yet cost him his leadership.

In what is set to be a dramatic showdown, the prime minister will set out how Mandelson was able to take up his role as UK ambassador without the Foreign Office revealing it had overruled the decision to fail his vetting.

Ahead of a showdown with MPs, prime minister looks like a man who is not really in control in his own government

Keir Starmer has spent much of the last 24 hours working on a plan for what senior government figures are already describing as his “judgment day”: his showdown with MPs on Monday over the latest Peter Mandelson revelations.

That the prime minister was apparently not told of Mandelson’s vetting failure has provoked incredulity across Westminster and accusations he sacked a senior civil servant to save his premiership.

Deputy prime minister says it is ‘inexplicable’ top civil servant kept Downing Street in dark

Keir Starmer would have blocked Peter Mandelson from serving as the UK’s ambassador to Washington had he known he failed security vetting, David Lammy has said, as he attempted to shore up the prime minister amid damaging fallout from the row.

In his first public comments on the vetting affair, Lammy said it was “inexplicable” that Oliver Robbins, the former top civil servant who was forced out of the Foreign Office this week, had opted to leave Downing Street in the dark over the outcome.

Keir Starmer understood to have lost confidence in official over decision to override security vetting failure

• Mandelson failed vetting but Foreign Office overruled decision

Sir Olly Robbins, the UK Foreign Office’s top civil servant, has been forced out of his post after the decision to fail Peter Mandelson during his security vetting was overruled by his department.

Robbins was the Foreign Office’s most senior official in late January 2025 when the decision was made, paving the way for Mandelson to become the US ambassador.