Voting systems in the UK

The House of Commons, devolved assemblies and mayors in the UK are elected using different voting systems. The House of Commons and the House of Lords use a variety of voting systems for internal elections

Voting systems

Voting systems, also known as electoral systems, are the method by which we elect representatives. A voting system determines the rules on how parties and candidates are elected.

A number of different voting systems are used to elect mayors and representatives to the House of Commons, Scottish Parliament, National Assembly for Wales, Northern Ireland Assembly, European Parliament and UK local authorities.

First-past-the-post

First-past-the-post is used to elect MPs to the House of Commons and for local elections in England and Wales.

Under first-past-the-post, the UK or local authority is divided into numerous voting areas, i.e. constituencies or wards. At a general or local election, voters put a cross (X) next to their preferred candidate on a ballot paper.

Ballot papers are then counted and the candidate that has received the most votes is elected to represent the constituency or ward.

Alternative Vote (AV)

The Alternative Vote is used to elect the majority of chairs of select committees in the House of Commons. The AV is also used for the election of the Lord Speaker and by-elections for hereditary peers.

Under AV, voters rank candidates in order of preference by marking 1, 2, 3 and so on next to names of candidates on a ballot paper. A voter can rank as many or as few candidates as they like or just vote for one candidate.

Ballot papers are then counted by using the first preference votes (i.e. those with a number 1 marked next to their name). If a candidate receives more than 50 per cent of the first preference votes then they are elected.

If no candidate reaches this 50 per cent threshold, then the candidate with the fewest first preference votes is eliminated. Their second preference votes are then reallocated to the remaining candidates. If after this stage one candidate has more votes than the other remaining candidates put together, that candidate is elected.

If not, the process of elimination and reallocation of preference votes is repeated until one candidate has more votes than the other remaining candidates put together, and is then elected.

Supplementary Vote (SV)

The Supplementary Vote system is used to elect the Mayor of London and other elected mayors in England and Wales.

The SV system is very similar to the AV system. Under SV, voters are limited to a first and second preference choice. A voter marks a cross in one column for their first preference candidate and another cross in a second column for their second preference (if they wish to do so).

The ballot papers are counted and if a candidate received more than 50 per cent of the first preference votes on the first count, then they are elected.

If no candidate reaches the 50 per cent threshold, the two candidates with the highest number of votes are retained and the other candidates are eliminated. The second preferences on the ballot papers of the eliminated candidates are counted and any cast for the two remaining candidates are transferred. The candidate with the most votes at the end of this process is elected.

Single Transferable Vote (STV)

The Single Transferable Vote system is used to elect the Deputy Speakers in the House of Commons. STV is also used for electing the Northern Ireland Assembly, local elections in Scotland and Northern Ireland and European Parliament elections in Northern Ireland.

Multi-member constituencies are required for STV which means constituencies are normally larger but elect several representatives rather than just one.

Under STV, voters rank candidates in order of preference by marking 1, 2, 3 and so on next to the names of candidates on a ballot paper. A voter can rank as many or as few candidates as they like or just vote for one candidate.

Each candidate needs a minimum number of votes to be elected. This number is calculated according to the number of seats and votes cast and is called a quota.The first preference votes for each candidate are added up and any candidate who has achieved this quota is elected.

If a candidate has more votes than are needed to fill the quota, that candidate’s surplus votes are transferred to the remaining candidates. Votes that would have gone to the winner instead go to the second preference listed on those ballot papers.

If candidates do not meet the quota, the candidate with the fewest first preference votes is eliminated and the second preference votes are transferred to other candidates. These processes are repeated until all the seats are filled.

Additional Member System (AMS)

The Additional Member System is used to elect the Scottish Parliament, the National Assembly for Wales and the London Assembly.

Under AMS, voters are given two votes; one for an individual candidate and one for a party. Individual candidates are elected to single-member constituencies using first-past-the-post (or the second ballot or alternative vote). Under the second, party vote, representatives (additional members) are elected proportionally to a larger region.

The percentage of votes obtained by the parties in the party vote (second ballot) determines the overall number of representatives including those elected for the single member constituencies after taking into account the seats gained in each region by each party in the first ballot.

Closed Party List

The Closed Party List system is used to elect Members of the European Parliament, with the exception of Northern Ireland which uses Single Transferable Vote.

A voter marks a cross on the ballot paper next to the party’s name they wish to support. Once the ballot papers have been counted, each party gets the number of seats proportionate to the number of votes it has received in each constituency.

Multi-member constituencies are required for the Closed Party List which means constituencies are normally larger but elect several representatives rather than just one.

As voters choose parties rather than candidates, it is for the parties to determine the order in which candidates appear on the list and are then elected.

Related information

Referendum on electing MPs

Find out more about the referendum on changing the voting system used to elect MPs to the House of Commons that took place on Thursday 5 May 2011.

Election and referendum basics

Parliament's Education Service supports young people's understanding of Parliament and democracy. Learn more about elections, referendums and voting systems.

Parliament and Constitution research

Read House of Commons Library briefing papers to find out more information about elections, parliament, devolution and the constitution.

Second ballot

Under the Second Ballot system a first-past-the-post election is held. If no candidate gets more than 50 per cent of the vote, the candidates who fail to reach a specified threshold are eliminated.

A second election is held (usually several days later) and the candidate who receives the most votes in this second ballot is elected.

Limited vote

Limited Vote systems use multi-member constituencies.  Voters, however, have fewer votes than there are available seats.

An electoral system used in multi-member constituencies in which electors have more than one vote, but fewer votes than there are candidates to be elected. The candidates with the most votes are elected.