Keir Starmer has revealed how he plans to take the fight to Andy Burnham - and keep his job as Prime Minister. It’s no secret that Mr Burnham, currently the Greater Manchester Mayor, plans to launch a leadership challenge if he wins the Makerfield by-election on Thursday and returns to Parliament as an MP.

Mr Burnham plans to issue Sir Keir an ultimatum over the weekend and demand that the Prime Minister name a date for his resignation. But it looks like Sir Keir insists he won’t give up his job without a fight. The Prime Minister made that clear this morning, when he said: “If there’s a leadership challenge from anyone. I’m not going to walk away, I’m going to fight it.” And today we learned that Sir Keir will set Mr Burnham a huge test.

The Prime Minister will argue that the focus of the entire Labour Party should be on winning the election to pick a new mayor of Greater Manchester - even though that could take weeks.

It would stop Mr Burnham’s momentum in its tracks.

And it would also make Mr Burnham look terrible if Labour actually loses that election (where Reform is likely to be the main challenger). Andy Burnham would get the blame for a humiliating loss.

We’ll hear this argument made by No 10 on Friday and over the weekend.

But Sir Keir gave us a preview in a TV interview this morning.

Asked about Mr Burnham, the Prime Minister told Channel 4 news: “He’s a huge asset. He’s been a fantastic mayor in Manchester. And if he comes back into Parliament, I hope he wins in the by-election, he’ll be a fantastic asset for our party and for the country.

“As soon as the by-election is over, we’ve then got a Manchester mayoralty to fight because that immediately is a huge by-election up in the northwest.

“So if Andy Burnham, the focus I think of the whole party will have to go to the Manchester mayorality because that will come up within weeks.”

And Sir Keir added for emphasis: “He’ll be a huge asset in Parliament, but for the first job for all of us is going to be the Manchester Mayoralty.”

Will it work? A lot of Labour MPs will have a lot of sympathy with the idea that Andy Burnham should take responsibility for ensuring their party holds on to Greater Manchester.

But many are also determined to force Sir Keir out.

Angela Rayner hinted Sir Keir must go, saying last night: “I think that it’s hard to escape the feeling that the public have had towards Keir.”

Former Health Secretary Wes Streeting has confirmed he will launch a leadership challenge.

And Sir Keir’s Cabinet colleagues are quietly lobbying to keep their jobs in a Burnham-led Government. That includes Home Secretary Shabana Mahmood and Foreign Secretary Yvette Cooper.

The Labour Party is preparing for a leadership change.

If Andy Burnham actually loses in Makerfield, then all bets are off. Keir Starmer might survive if his main rival is Wes Streeting.

But many Labour MPs and activists have convinced themselves that Mr Burnham, if he returns to Parliament, is their only chance of avoiding disaster at the next General Election.

It may already be too late to stop him.