What happens when a British Prime Minister resigns?

UK Prime Minister Boris Johnson announced his resignation as Conservative leader on Thursday following mounting pressure from lawmakers in his own party to stand down.

Under the UK political system, between elections, only Conservative members of Parliament have the power to remove a sitting Conservative Prime Minister.

So, what happens to the UK government when a Prime Minister resigns, and how is a new leader elected?

No. It starts the Conservative Party process for choosing a new leader of the party.

UK Prime Ministers are not directly elected by the people; Johnson is Prime Minister because he is the head of the largest party in the House of Commons.

The Conservatives will still be the largest party after Johnson quits, so the new head of the party will become Prime Minister.

Leadership candidates need the support of at least eight lawmakers.

If there are more than two candidates, Conservative Party lawmakers hold round after round of votes to whittle the number of leadership candidates down to two.

Then Conservative Party members nationwide vote -- by mail -- between the two finalists.

Who is Prime Minister while all this happens?

Johnson indicated in his resignation speech that he plans to stay in office until a successor is chosen.

That's what would happen under normal circumstances: A Prime Minister who has resigned as party leader stays in office as caretaker Prime Minister until there is a new party leader.

But it's not clear that the Conservative Party will stand for that in Johnson's case.

One alternative would be for Deputy Prime Minister Dominic Raab to step in as caretaker. There's no precedent for that -- but there's also no precedent for more than 50 government officials to resign in two days in order to force a Prime Minister out.

Is there any way to force Johnson to leave before a new Conservative Party leader is chosen?

Conservative lawmakers could, in theory, try to force him out themselves by calling a vote of confidence among Tory MPs. But Johnson survived a vote like that just a month ago.

Under current party rules, that means there can't be another party confidence vote in him for 12 months.

The rules could be changed, but it's not clear the Conservative Party wants to start that kind of infighting when Johnson has already said he's going, and when a leadership contest is underway.

Can't the opposition do anything to force Johnson out?

Labour leader Keir Starmer said Thursday that if the Conservatives didn't push Johnson out immediately, the opposition would call a confidence vote in the government among the entire House of Commons.

If the opposition won, it could theoretically lead to a general election -- but even with all the chaos in the Conservative Party at the moment, they still have a big majority in the House of Commons, and they're not likely to want a general election at the same time as a leadership election. So the chances of the opposition bringing the government down now are slim.

When Johnson does finally leave Downing Street, what happens?

He submits his resignation to the Queen, in person.

The Palace will announce officially that Queen Elizabeth II has accepted Johnson's resignation, and will say who she has invited to become Prime Minister to replace him. That person will then go to meet the Queen to accept the invitation. This is a formality.

Does the new Prime Minister have to call a general election?

No. The United Kingdom isn't scheduled to have another general election until December 2024.

The new Prime Minister could choose to ask Parliament to vote for an early election but isn't required to do so.