A contest for the election of a new leader of the Conservative Party takes place when the current leader resigns or loses a vote of no confidence among his own deputies.
To raise a vote of no confidence, 15% of the Tory delegates have to write to the Chairman of the 1922 Backbench Committee, currently Sir Graham Brady.
With 316 Conservative MPs in the House of Commons, Sir Graham must receive 48 letters to call a ballot.
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If Theresa May decided to fight, she would need the support of more than 50% of Conservative MPs – currently 159 – to stay in office.
But even if she did reach that threshold, a narrow victory would seriously undermine her authority and lead her to ask whether it is worth continuing.
If she lost her voice, she would not be able to pass the subsequent Leadership Contest, which was arranged by the chairman of the & # 39; 22.
Candidates for leadership must be nominated by two Conservative MPs. If only one candidate emerges, he or she becomes the leader.
If a number of would-be leaders are nominated, the list of MPs will be reduced to a shortlist of two before being presented to Party members in the country.
In a series of secret ballots taking place in Westminster within a few days, MPs select their preferred leader, eliminating the least popular candidate after each round until only two remain. The last two then go to a postal vote of all party members. with the position of leader and prime minister, going to the winner.
Sir Graham would be responsible for monitoring the competition and setting a timetable for the campaign, which would probably take around 12 weeks.
Ms. May could remain in office during the election campaign.
With October's goal of closing the UK exit agreement and reaching political agreement on future relations with Europe, there is likely to be pressure for a shorter campaign to quickly find a leader.
Only the members of the Party or the Scottish Party who were members at the time of the call for nomination for the leadership and who were members at least three months before the end of the vote are eligible to vote.
Tory membership stood at 124,000 in March this year.
On average, the members are older and more enthusiastic about Brexit than either MPs or conservative voters.
Since the adoption of the current rules in 1998, members have elected Iain Duncan Smith over Kenneth Clarke in 2001 and David Cameron over David Davis in 2005.
In 2003, Michael Howard was the only candidate and in 2016, Ms. May became leader without a vote from members after her only rival, Andrea Leadsom, had moved out.