Chris Mason: Burnham's emphatic win leaves Starmer and Labour MPs with big decision

Andy Burnham couldn't have hoped for a better result than this.

He has won and won big time, taking more votes than all his rivals combined.

Granted the Makerfield parliamentary seat has elected Labour MPs for yonks, but just a matter of weeks ago, at the local elections, Reform UK were dominant in this collection of towns broadly to the south of Wigan – places like Abram, Hindley, Orrell and Winstanley.

It has allowed Burnham and his team to road test an argument here – and we can expect to hear more of it in the coming days and weeks – that he is the Labour figure, unlike Sir Keir Starmer, who can beat Nigel Farage and Reform.

And so, the coming argument will go, he ought to be their party leader and your prime minister.

Burnham's popularity and capacity to beat Reform in Greater Manchester is proven. What isn't is the extent to which this would extend around the country.

That was a by-election campaign and a results night like no other. I have covered umpteen by elections, but none as significant as this.

A total of 77,478 people were given the chance to choose a new MP explicitly because one of the candidates, Andy Burnham, wants to become prime minister and do so quickly.

And Burnham was, to all intents and purposes, campaigning against his own party's governing record at Westminster.

Extraordinary, when you think about it.

Live: Reaction as Andy Burnham wins Makerfield by-election

Burnham says his win in Makerfield by-election could be turning point

Burnham says 'this is a final chance to change' in his victory speech

His victory speech, in the middle of the night, was, paragraph by paragraph, implicit about his ambitions and in totality almost explicit.

"Tonight could be a turning point," he said. "This is a final chance to change," adding that this was a result that could "bring about a country that works for everybody".

These are not the typical sentences of a by-election winner.

We can expect to see Burnham back in front of the cameras later this morning, although I am told we shouldn't expect him to elaborate on his wider ambitions beyond what he has already said.

We will also hear from the prime minister. How does he choose to respond?

While the polls were still open, his allies were on the phone trying to make his case.

They were arguing that the gap in the polls nationally between Labour and Reform isn't atypical for this point in a parliament.

They were arguing that "things are turning around" as one senior figure put it – pointing to the net migration numbers, economic growth and the money going into public services.

But the prime minister will wake up to see the stonking scale of Burnham's victory. Will it shift his outlook, his defiance, so frequently recently expressed?

Will it mean more Labour figures, from the cabinet down, privately – or publicly – call for him to go?

One previously loyal Labour MP, Patrick Hurley, has this morning called for the PM to go, saying: "To everything there is a season and I think right now we need a transition to something new."

If that were to happen at scale, it may become obvious that Sir Keir can no longer viably govern.

But if it doesn't and this result here doesn't dilute his defiance, it will be up to his potential successors, Andy Burnham and Wes Streeting among them, to make a decision.

Who is willing – and when – to stick their head above the parapet and say they are launching a formal challenge?

We are in for a lively few days and weeks, I suspect.

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