Sir Keir Starmer faces the biggest threat to his premiership after Andy Burnham romped to victory in the Makerfield byelection – and has his eyes set firmly on the top job.
The Greater Manchester Mayor – who will have to resign now he is an MP – is expected to mount a leadership bid after the stonking victory saw him beat Reform's Rob Kenyon by almost 10,000 votes. And Labour MPs have already called for Sir Keir to step aside.
Rachael Maskell, MP for York, told the BBC: "Many of us are impatient to deliver for our constituents and we see the best path for that is with Andy Burnham leading." Here, we take a look at what could happen next as the King of the North heads to Parliament.
Will Starmer Quit?
A Labour leadership election can only be triggered if the leader resigns, or if 20% of MPs nominate a challenger, which currently translates to 81 MPs.
Sir Keir has repeatedly refused to stand down and vowed to fight any challenge. It seems highly unlikely the PM will stand down. And he said on Friday he "will stand" in a Labour leadership contest should one be triggered, adding he will not "walk away".
As current leader, he is automatically entitled to appear on the ballot paper to defend his position if a contest is triggered.
Possible Peaceful Transfer of Power
While he has vowed not to quit, it is hoped by many MPs that Sir Keir could cut Burnham a deal, for example setting out a timeframe for him to stand down at party conference in September.
This would let Burnham prepare for power and build a team while avoiding a bloody civil war within the party. However, it seems unlikely as Sir Keir this week said Burnham was a "huge asset" and offered him a cabinet role, which was rejected out of hand.
And it would likely create a power vacuum in Westminster and see ministers reluctant to make big decisions as the PM would effectively be a sitting duck.
Who Else Could Stand for Leader?
If Sir Keir digs his heels in, his MPs could trigger an election contest by backing an alternative candidate. Wes Streeting, who stepped down as Health Secretary last month, suggested this week that he could be prepared to trigger a contest after the weekend.
He previously said he would stand in any contest to replace the prime minister. Ed Miliband, Al Cairns and Angela Rayner are also floated as possible contenders.
Burnham, who visited Westminster before the by-election was called, is said to already have the 81 names needed to secure the backing to trigger a contest and is odds on with the bookies to replace Sir Keir. And some MPs have already openly called for Starmer to go.
How Does Voting Take Place?
Only Labour Party members and affiliated trade union supporters are allowed to vote in the party's leadership contests. It uses a one-person-one-vote system, meaning that the same person cannot vote both as a trade union member and as a Labour Party member.
Eligible voters then cast their votes using a preferential voting system. Each voter ranks the candidates in order of preference by marking their ballot 1, 2, 3 and so on. The winner is the first candidate to secure over 50 per cent of the vote.
If a candidate does not win on the first round, then the candidate in last place is removed, and the votes are redistributed and counted again. Several rounds can take place until a candidate wins the 50 per cent needed.
What Happens When a Leadership Battle Is Called?
There is no official timetable for a Labour leadership contest. It is up to the National Executive Committee (NEC) to lay out the timings, which they will do once a contest has been triggered. But they can take a couple of months from start to finish.
The new Labour leader would automatically become the prime minister too, without the need for a general election. By beating Reform so heavily, many see Burnham as being Labour's last chance saloon to see off Farage's party at the next general election.
And internal polling shows Burnham is the only Labour figure that would beat Sir Keir in a leadership contest.
