Explainer-How could British Prime Minister Keir Starmer be ousted by unhappy lawmakers?

LONDON (Reuters) -British Prime Minister Keir Starmer was battling to maintain his authority over his party on Wednesday after one of his most senior ministers criticised the "toxic" culture in his team and was forced to deny he planned a leadership bid.  

Wes Streeting, the health minister, accused Starmer's allies of trying to "kneecap" him with the briefings and condemned what he called the "self-defeating" attacks on him coming from Downing Street.

Here is an explanation of how Starmer could face a leadership challenge under the governing Labour Party's rules: 

WHAT NEEDS TO HAPPEN FOR THERE TO BE A LEADERSHIP CONTEST?

A leadership challenge can be triggered if 20% of Labour members of parliament support a candidate to replace Starmer. 

There are currently 405 Labour members of parliament, so 81 would be needed to support a candidate to replace him.

Starmer would automatically be on the ballot paper in any contest.

Labour members and affiliates, including the trade unions, would be able to vote in a ballot.

The timing of any contest would be decided by Labour's National Executive Committee, made up of party lawmakers and other members.

COULD THIS HAPPEN TO STARMER?

There is growing unhappiness with Starmer's leadership in his party. But so far only a handful of lawmakers have publicly said he should be removed as he struggles to revive a stagnant economy and halt the rise of the Reform UK party led by the Brexit campaigner Nigel Farage.

Starmer's finance minister has indicated she is likely in her budget later this month to break the party's election manifesto promise not to raise income tax, social security contributions, or value-added tax on working people.

Such a move would leave Starmer's party, already languishing more than 10 percentage points behind Reform in the polls, facing allegations that it misled voters.

Labour parliamentarians say it is more likely that Starmer could face a challenge if the party performs badly in elections in Scotland, Wales and some English councils in May next year.   

It is generally harder for Labour lawmakers to remove a prime minister than the rival Conservative Party, who went through five prime ministers in eight years between 2016 and 2024, because the Labour rebels would need to agree on one replacement rather than just a no confidence in the leader.   

Labour members of parliament have never successfully removed a sitting prime minister in the party's 125-year history.  

Former Prime Minister Tony Blair set a deadline for his departure after some junior members of his government resigned in 2006, but he did not quit immediately.  

WHO ARE THE POSSIBLE CONTENDERS TO REPLACE STARMER?

Streeting is considered the bookmakers' favourite. But he is publicly supportive of Starmer and condemned what he called "destructive" attacks on him coming from Downing Street.  

Manchester mayor Andy Burnham – who served as a minister during previous Labour governments – is the second favourite, despite not currently sitting as a member of parliament.

The interior minister Shabana Mahmood, the foreign minister Yvette Cooper, and former deputy prime minister Angela Rayner are considered other possible candidates.  

(Reporting by Andrew MacAskillEditing by Ros Russell)