A leadership election is automatically triggered if the leader either requests one, dies, becomes incapacitated, ceases to be an MP or resigns from the leadership.
There are also two ways to force a leadership contest. Liberal Democrat MPs can pass a vote of no confidence in the leader (with a simple majority required), or at least 75 local parties must request an election (following the decision of a quorate general meeting).
The Liberal Democrat Federal Constitution also requires that there be a leadership election within a year of each general election. There are two exceptions to this: if the leader is a member of the Government, or if the Liberal Democrat Federal Board votes to postpone the leadership election for a year by two-thirds majority.
The national parties (Welsh Liberal Democrats and Scottish Liberal Democrats) have separate constitutions and different electoral rules apply for the election of their leaders.
A leadership candidate for the Liberal Democrat Federal Party must be a Liberal Democrat MP, gain support from at least 10% of other Liberal Democrat MPs, and be supported by at least 200 members from more than 20 local parties. They must also indicate acceptance of their nomination.
The Lib Dems use a one member, one vote system. Anyone who is a party member on the day nominations close can vote in a postal ballot.
The election technically takes place using the Single Transferable Vote system. This is a form of proportional representation which the Liberal Democrats have long been committed to. However, when there is only one leadership position available, this effectively works in the same way as the Alternative Vote system. In practice this means that if one candidate gets more than 50% of the vote, they are elected. If no candidate manages this, then the candidate who came last is removed and their votes are redistributed to voters’ second preference candidates. This process is repeated until one candidate has more than half of the votes.
The election takes between nine and 13 weeks (including a minimum of 15 days to collect nominations, 21 days to dispatch ballot papers and 21 days to return ballot papers).
Unlike the Labour Party, Liberal Democrat leadership elections can take place at any time of year. The returning officer can postpone or suspend elections if they clash with a general election or referendum.
If the leader becomes permanently unavailable, the deputy leader (or, if there is no deputy leader, the chief whip) becomes acting leader of the parliamentary party. They assume joint responsibility for being leader (along with the president of the party) until the new leader is elected. (The president of the party is Chair of the Federal Board, which is responsible for co-ordinating party strategy and the work of the Federal Party – they are nominated and elected by party members).
There was attempt in early 2019 to make changes to the electoral rules. These changes would have allowed registered supporters to vote in the leadership contest (in a similar way to the Labour Party). They would have also allowed non-MP Lib Dems to become leader. However, they were rejected at the Spring 2019 Liberal Democrat Conference in York. Although there will still be a registered supporters scheme, those who become registered supporters will not be able to vote in leadership elections.