The process of electing the leader of the Conservative party has changed and evolved several times during its 183 year history.
Since 2005 the process of electing the Conservative leader has been a three stage process, nomination, parliamentary balloting and party balloting.
To be a candidate for leadership an MP must be nominated and seconded by fellow MPs, once a valid nomination has been accepted by the Chairman of the 1922 committee who acts as the returning officer a candidate is put forward to the parliamentary balloting stage.
At this stage Conservative MPs vote for their preferred candidate, the candidate with the lowest votes at the end of each round is eliminated and the parliamentary balloting continues until only two candidates are left.
When only two candidates remain these names go forward to the party balloting stage where every Conservative party member has the right to vote for their preferred leader, the candidate with the most votes becomes leader of the Conservative party. Since being founded every Conservative party leader has been either Prime Minister or Leader of the Opposition and sometimes both.
However, this was not always the case. Before being formed as the modern conservative party in 1834 it was the Tory Party, a nickname still used to this day. Leadership was often shared by the royal favourites at the time, back in 1710 leadership was shared by the Duke of Marlborough and the Viscount Bolingbroke.
By the 1780s the way in which leaders where decide was by meetings of the parliamentary party, who would chose who they wanted to be leader of the party through an informal closed meeting of those at the top of the party, former leaders, cabinet members ect, this process lasted all the way until the middle of the 20th Century when Edward Heath became the first elected Conservative party leader.
1965 marked the first formal election for the leader of the Conservative party. The rules the election was run under needed a candidate to have an absolute majority of votes cast and a 15% lead over the second place candidate of all votes cast.
In 1975 a rules review was conducted changing the 15% lead needed over the second placed candidate of the votes cast to a 15% lead of the entire electorate and allowing for a sitting Leader to be challenged, previously an election was only possible once a vacancy had occurred. This process lasted until the 2005 review and rule change.