Chris Mason: Starmer prepares to face Labour MPs knowing his future is in the balance

The government is teetering - and how long the prime minister now lasts is a live, legitimate and open question.

Today has been extraordinary and it is not over yet.

Westminster had barely had time to digest the departure of the prime minister's chief of staff Morgan McSweeney, when we learnt that his Director of Communications Tim Allan was off as well.

That happened shortly before lunchtime, the latest case study in a prime minister appearing rudderless and no longer in control of events.

And shortly after lunchtime what looks like could be a game changing moment – the leader of Scottish Labour, Anas Sarwar, calling on the prime minister to quit.

Context here is key: at the time of the general election, Sarwar was the favourite to be Scotland's next first minister.

It was widely expected that Labour would defeat the Scottish National Party in the elections to Holyrood in May 2026.

It doesn't look like that now. The SNP are confident they can secure a mandate to head into their third consecutive decade of devolved power.

It is this brutal truth that has prompted Anas Sarwar to be as devastatingly outspoken as he has.

His intervention is a horrible reality Keir Starmer will struggle to escape - if he manages to survive in the short term, the verdict of his Scottish leader will be forever thrown at him.

As an indicator of the magnitude of the moment, it was after that intervention that came the torrent of posts on social media from members of his cabinet.

One by one supportive messages have appeared from senior ministers - as have posts from former deputy Labour leader Angela Rayner and the current deputy leader of the party, Lucy Powell.

The kind of thing that should be utterly conventional – a cabinet minister publicly supporting the prime minister – became newsworthy today, because frankly it wasn't certain they would.

Next, Sir Keir will head to address his MPs in Parliament this evening.

Never before has his future been so imperilled, never before in his time in politics has his back been this far against the wall, with a sceptical audience in front of him asking if he really is the best person to lead them.