(Sharecast News) - Prime Minister Keir Starmer is reportedly set to resign as early as Monday and set out an orderly exit following Andy Burnham's Makerfield by-election win.

Starmer insisted on Friday that if there was a leadership challenge, he would fight it. He told reporters at an event in London: "If there is a contest, just to be clear with you, then, yes, I will run."

However, according to The Telegraph, citing a senior government figure, Starmer has realised the "game is up" and "quite a bit of movement" among cabinet ministers since Burnham's Makerfield victory have caused the PM to reconsider his previous commitment to battling on.

One Labour MP, who is usually considered to be a loyalist to the PM, told the paper he believed Starmer would announce his departure date as soon as Monday given that his support among MPs was now down to only a handful of "friends and family".

"There's no one left. Literally people whose relatives work in No 10 or people who are long term personal friends of Keir's are pretty much the only ones left," they said, adding that trying to stand in the way of Burnham's path to Downing Street was "like trying to fight gravity".

Meanwhile, The Sun cited a senior ally as saying: "I think there is just a 25% chance he fights on now."

According to The Observer, the PM has concluded that his position is no longer tenable after conversations in recent days with cabinet ministers, Downing Street advisers, trade union leaders, and party donors.

Although Starmer is spending the weekend talking his future over with his wife at Chequers before making a final decision, senior Labour figures believe a "clear statement" could come as early as Monday.