If a Conservative prime minister resigns as leader of the party, this triggers a contest for a new leader. They could choose to stay as Prime Minister until a new leader is elected, or resign in favour of another Conservative MP who would temporarily be Prime Minister until the leadership contest is over. This would be an unusual situation.
If they resign as Prime Minister or are defeated in a general election, they can remain leader until a new leadership contest.
The UK has de facto caretaker governments during general elections but not during leadership challenges. So the Government and the civil service functions without change.
The Prime Minister in place during a leadership contest would still have all the powers of the Prime Minister.
The election takes place in two stages. In the first stage (shortlisting), Conservative MPs put their own names forward. In the 2019 leadership election candidates will need the support of eight MPs (proposer, seconder and six others) to stand. In the 2016 leadership election, candidates only needed the nominations of two other MPs.
MPs then vote in a series of rounds to whittle down the candidates. In each round, the candidates who don’t meet a certain threshold of votes are eliminated. In 2019, for the first ballot, this will be 5% of Conservative MPs (more than 16 MPs), and 10% of Conservative MPs in the second ballot (more than 32 MPs). For all subsequent ballots, the candidate who comes last is eliminated, until there are only two candidates remaining. In previous leadership elections, the candidate who received the least votes in each round was eliminated.
In stage two, the party membership is balloted on which of the two candidates they prefer.
The timescale for each contest is set out by the 1922 Committee. The outline timetable suggests that the first stage of the 2019 leadership contest will take two weeks, starting on the 7 June and finishing on the 20 June. Stage Two is expected to take a month, with the new leader announced in the week beginning the 22 July.
In 2016, the whole process was scheduled to take two months, but was not needed after Andrea Leadsom withdrew following the second ballot and Theresa May became leader.
The rules by which the 1922 Committee (a committee representing backbencher Conservative MPs) arranges the first stage of a Conservative leadership contest and votes of no confidence are not published. They can be changed at any time by the 1922’s Executive Committee (in consultation with the Conservative Party Board, which is made of representatives from each section – voluntary, political and professional – of the party). This means, for example, that the rule that means a new vote of no confidence cannot be triggered for 12 months could be removed with little to no notice.
The second stage is guided by the Conservative Party Constitution – changes to this must be decided by the Constitutional College of the Conservative Party, which is an electoral college made up of the National Conservative Convention (representatives of the voluntary wing), MPs, MEPs and the representatives of Conservative Peers. However, the exact rules for the conduct of the ballot are decided by the Conservative Party Board and the Executive Committee of the 1922 Committee.
Conservative Party MPs can initiate a no confidence vote in the Prime Minister when 15% (48 MPs) of Conservative MPs write to the party’s 1922 Committee Chair, currently Sir Graham Brady MP.
This vote is then scheduled by the chair in consultation with the party leader. This can happen quickly. For example, the recent confidence vote in Theresa May was held on the 12 December, the day after she was informed that the 15% threshold had been reached. MPs then vote in support or against the leader.
If more than 50% of all Conservative MPs vote in support (158 MPs) of the Prime Minister, they can stay as party leader and under current rules no new vote can be triggered for 12 months. They remain as Prime Minister.
If the Prime Minister lost the confidence vote among Conservative MPs, they would not be able to stand again. But any other candidate could stand in a new leadership contest.
There is no other formal method by which to initiate a leadership challenge. However, there are ways for the rest of the party to express a lack of confidence in the leader.
The National Conservative Convention (NCC) is a body representing the voluntary wing of the party, made up of association chairs, area and regional officers and specialised groups (such as Young Conservatives and the Conservative Women’s Organisation). In April 2019, more than 65 Conservative Association Chairmen signed a petition calling for an extraordinary general meeting of the NCC. This was significant as it passes the threshold required to hold an extraordinary general meeting as laid out in the Conservative Constitution.
Read our explainer on the contenders in the 2019 Conservative Party leadership contest and their proposals for government.