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

LONDON, May 14 (Reuters) - British ​Prime Minister ⁠Keir Starmer's position is under serious threat after senior minister Wes ​Streeting quit and dozens of Labour 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.

Health minister Wes Streeting resigned on Thursday, saying Starmer wouldn't lead the ⁠party for much longer and should facilitate a leadership race with the best ⁠possible field of candidates.

That followed dozens of lawmakers calling ​for Starmer's departure after his appeal for another chance seemingly fell on deaf ears. The number has now risen to above 90.

ISN'T THAT ENOUGH?

No. Starmer has insisted he is getting on with the job and won't resign, and 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. Streeting's resignation letter endorsed that approach.

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 lawmakers, including the challenger.

A source close to Streeting said that he had the numbers to trigger a challenge, but had not done so as ‌he favoured an orderly timetable with a broader field of candidates, though Starmer's allies said Streeting didn't have the numbers.

Once a candidate submits their list of backers to Labour Party officials, the party's National Executive Committee will meet to finalise the rules of the leadership ​race.

Other candidates will then be able to seek nominations from lawmakers to run for leader once the contest is underway, at which point candidates also must ‌hit thresholds for support from grassroots Labour Party organisations, and from affiliated organisations such as trade unions.

Any challenger has to be a lawmaker. The mayor of Greater Manchester Andy Burnham, who polls favourably with Labour members among the candidates to replace Starmer, would need to find ⁠a parliamentary seat ⁠to contest and win before he could stand to be leader.

Starmer would have an ‌automatic right to be on the ballot paper if he chose to fight the contest. He would not need nominations from lawmakers but could still seek their endorsement, ​to demonstrate what support there ​is for him and ensure that his backers didn't nominate other candidates.

If only one candidate ‌meets the threshold for support, 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. (Reporting by William James and Alistair Smout; Editing by Alex Richardson and Philippa Fletcher)