Prime Minister Keir Starmer says he will resign, paving the way for Britain to have its seventh leader in 10 years.
Here's what happens next:
HOW DOES A LEADERSHIP CONTEST WORK?
* Any candidate wishing to replace Keir Starmer will need to secure the support of 20 per cent of Labour members of parliament - with Labour currently holding 403 seats, that equates to 81 MPs, including the challenger
* Candidates must hit thresholds for support from grassroots Labour Party organisations and affiliated organisations such as trade unions
WHO GETS TO DECIDE THE WINNER?
* If more than one candidate qualifies, the winner is decided by a ballot of all Labour Party members and affiliates, and the winner then becomes prime minister
HOW LONG WOULD IT TAKE?
* Though the timeline is officially decided by the party's governing body, Starmer said nominations would open on July 9 and close before parliament goes into recess, which is scheduled for July 16
* If there is a contest, he said it should be completed by the time parliament returns, scheduled for September 1
WHAT HAPPENS IF THERE'S ONLY ONE CANDIDATE?
* 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
