Keir Starmer is pulling out all the stops today as he confronts a pivotal moment in the House of Commons that could determine his political future.

Downing Street is exerting maximum effort to prevent Labour MPs from breaking ranks during a critical vote on whether the Prime Minister misled Parliament in relation to the Mandelson scandal.

Party whips have cautioned that MPs who do not support Sir Keir risk expulsion from the party. In addition, ministers have been actively reaching out to persuade any MPs who might be undecided.

Highlighting the gravity with which No. 10 is approaching the situation, former Prime Minister Gordon Brown has been called upon to denounce the suggestion of referring Sir Keir to the privileges committee.

Yet, even as the high-stakes Commons debate is set to commence at midday, Starmer is already facing further challenges.

This morning at 9 a.m., Philip Barton, a former chief at the Foreign Office, is scheduled to appear before the foreign affairs committee. He is anticipated to reveal that Downing Street applied pressure to expedite Mandelson’s appointment as the US ambassador.

Sir Keir’s former chief of staff Morgan McSweeney will then be grilled by the MPs – his first significant public appearance since the furore erupted.

Keir Starmer is going all-out to save his skin today as he faces a Commons showdown that could decide his fate

The PM has been struggling to cling on amid the ongoing scandal over Mandelson (pictured) being made US ambassador

Sir Keir’s former chief of staff Morgan McSweeney will be grilled by MPs this morning – his first significant public appearance since the furore erupted

Former shadow chancellor John McDonnell said Sir Keir should refer himself to the privileges committee

Defeat for the PM would trigger a formal inquiry by the privileges committee, throwing his floundering government deeper into a tailspin.

A major arm-twisting operation is in full effect, with a three-line whip in place for Labour MPs to support the Government.

That is in stark contrast to when Sir Keir called a similar vote against Boris Johnson over Partygate. At that point he argued that MPs should be free to follow their own consciences. 

Writing in the Daily Mail today, Kemi Badenoch said MPs of all stripes have a duty to hold Sir Keir to account for treating Parliament with ‘contempt’.

She told Labour backbenchers they are ‘not in the Commons simply to protect the PM from embarrassment’.

‘Labour MPs now face a test of their own,’ the Tory leader said.

‘They can circle the wagons, obey the Whips and tell themselves this is just politics. Or they can remember they are MPs before they are members of the Labour Party.’

Allies of Sir Keir are confident they can hold restive Labour MPs at bay, with crucial local elections barely a week away.

The PM told a packed meeting of the Parliamentary Labour Party last night: ‘When we stick together and fight together we are so much stronger.’

He sought to dismiss the Commons vote as a ‘stunt’ ahead of the May elections.

‘I have responsibility for being totally transparent with you, with Parliament and the British public,’ he said.

‘I take that very seriously as well. But this is not about a lack of transparency.

‘This is a political stunt by our opponents who want to bring us down, obscure our message, stop us getting on with our work.

‘And the timing tells you everything, nine days before local elections.’

He said the Conservatives had put forward ‘totally baseless’ and ‘absolutely ridiculous’ accusations against him and insisted the motion on Tuesday was ‘pure politics’, adding: ‘We need to stand together against it.’

The Privileges Committee was responsible for Mr Johnson’s exit from frontline politics after it investigated him for misleading the House over the ‘Partygate’ breaches of Covid laws in Downing Street.

He quit as an MP in 2023 before the committee published a report recommending his suspension.

The Government also took the unusual step last night of publishing a letter from former cabinet secretary Sir Chris Wormald to the PM, in which he said he had concluded the ‘appropriate processes were followed’ in both the appointment and sacking of the peer.

Sir Keir has also faced questions for insisting to MPs that ‘no pressure existed whatsoever in relation to this case’ after former top Foreign Office official Sir Olly Robbins said there had been ‘constant chasing’ from No 10 while checks were taking place for the ambassadorship.

Sir Olly’s claims were echoed in written evidence to the Foreign Affairs Committee published last night from another key figure in the security process.

According to a letter from the Foreign Office drafted in consultation with Ian Collard, who was head of security in the department, the official said he ‘felt pressure to deliver a rapid outcome’ to the clearance procedure.

This was in light of ‘regular contact from No 10 to the FCDO (permanent under-secretary’s) office,’ the letter said, although Mr Collard did not personally speak to Downing Street colleagues and ‘does not assess that this pressure influenced professional judgment that was reached by himself or his team’.

The PM has been accused of misleading MPs by saying ‘full due process’ was followed in appointing Lord Mandelson, who was given developed vetting status despite failing security checks.

The Foreign Office, under then top civil servant Sir Olly, cleared him despite red flags raised by experts at the UK Security Vetting (UKSV) agency.

Mr Collard, who briefed Sir Olly on the vetting findings, also did not see the UKSV file recommending clearance be denied, according to the letter published on Monday.

Instead, he received an oral briefing from officials which led him to believe Lord Mandelson’s case was ‘borderline’ and that ‘the risks could be mitigated,’ the evidence said.

Commons Speaker Lindsay Hoyle granted the request for a vote on referring Sir Keir to the privileges committee 

She said: ‘The Prime Minister misled the House of Commons repeatedly. He appointed a national security risk and friend of a convicted paedophile to be our ambassador in Washington, our most sensitive diplomatic post’

Mr Brown urged Labour to unite in focusing on putting ‘the needs of the country first’ in a statement.

‘Whatever the parliamentary games at Westminster, what the country expects of everyone in Labour is to focus on the priorities of the British people, which is what Keir Starmer is doing and for which he deserves all our support,’ he said.