Why didn't Keir Starmer fire Peter Mandelson yesterday?

Peter Mandelson's position was completely unsustainable, but it took Sir Keir Starmer 24 hours after everybody else to realise the inevitable.

In the chaotic interim, this generated the extraordinary spectacle of No10 saying that they had full confidence in their man in Washington because - and it feels incredible to type this - No10 had been fully aware that the peer had an extended relationship with a convicted paedophile after the point he had been to jail in the US, and was content with this situation.

An incredible state of affairs.

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This is why the issue has become a matter of Starmer's judgement almost as much as Peter Mandelson's.

Indeed, there were echoes here of the Chris Pincher affair that led to Boris Johnson's downfall - a leader stubbornly defending acts which revolted the bulk of the party, in a tone deaf act of self-harm.

And revolted, they were.

Almost the entire Labour Party was reacting with horror at the revelation, and even more so at the defence.

Less than 24 hours before his departure, Starmer was saying: "The ambassador has repeatedly expressed his deep regret for association with him, he's right to do so. I have confidence in him and he's playing an important role in the UK-US relationship."

Words of certainty - but done once again without access to full facts.

Read more:Starmer sacks Mandelson as US ambassadorAnalysis: Mandelson is never far from a scandal

Dangerously, the PM was also defending a vetting process which would by implication put him in possession of facts that should have ruled Mandelson out of that job.

"Full due process has gone through when the appointment was made," he said.

Now the line from a junior foreign office minister is that Mandelson hadn't told him. So either the vetting failed or this isn't quite accurate.

My understanding is that no one in government knows the last time Mandelson did see Epstein - the absence of certainty on that key fact must have set off alarm bells.

Right now, No10 will be thinking and hoping that, with just six days to go until the state visit by Donald Trump, which was meant to be organised by Mandelson, people will not focus too much on this question.

However, given the current rate of one big beast in government being sacked every week, this will ultimately land at Starmer's feet.