EXPLAINER: What happens if the UK's Starmer quits, or is challenged?

British Prime Minister Keir Starmer's position is under serious threat after dozens of his own lawmakers called for him to set out a timetable for his departure, or resign, in the wake of heavy losses in local elections.

Here's what could happen next:

HAS A LEADERSHIP CONTEST BEEN TRIGGERED?

Not yet.

On Monday, several ministerial aides stepped down and more than 70 Labour lawmakers publicly called for Starmer's departure after his appeal for another chance seemingly fell on deaf ears.

Some senior cabinet ministers, according to media reports, have told Starmer to announce a plan for his exit.

ISN'T THAT ENOUGH?

No. Labour has strict rules governing the removal of a party leader and the system requires lawmakers to coalesce around specific candidates rather than just express "no confidence" in their current leader.

At the moment most of those against Starmer have called for him to set out a timetable for his own departure - effectively asking him to resign without needing to be forced out.

One former junior minister, Catherine West, has made a formal attempt to gauge support for Starmer's exit but this is not the same as a leadership challenge and she has not declared her intention to stand to replace him.

IF HE DOESN'T RESIGN, HOW WOULD A CHALLENGE WORK?

Any candidate wishing to make a challenge would need to secure the support of 20% of Labour members of parliament. With Labour currently holding 403 seats, that equates to 81 backers.

Candidates also must meet thresholds for support from grassroots Labour Party organisations, and from affiliated organisations such as trade unions.

Starmer would have an automatic right to be on the ballot paper, if he chose to fight the contest.

If only one candidate qualifies, there is no vote: the candidate is elected unopposed as Labour leader and becomes prime minister.

If more than one candidate qualifies, the winner is decided by a ballot of all Labour Party members and affiliates. The winner then becomes prime minister.

-William James/Reuters