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

The House of Commons, Scottish Parliament, National Assembly for Wales, Northern Ireland Assembly, European Parliament and UK local authorities use different voting systems.

First-past-the-post

The House of Commons and local councils in England and Wales use the first-past-the-post system.

The UK is divided into constituencies. Local authorities into wards.

At a general or local election, voters put a cross (X) next to their preferred candidate on a ballot paper. Ballot papers are counted. The candidate with the most votes represents the constituency or ward.

Alternative Vote (AV)

Alternative Vote is used to elect:

chairs of most committees in the House of Commons

the Lord Speaker and by-elections for hereditary peers.

Voters rank candidates in order of preference by marking 1, 2, 3 and so on. A voter can rank as many or as few candidates as they like or vote for one candidate.

First preference votes are counted first. If a candidate receives more than 50 per cent of the first preference votes then they are elected.

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

If not, the process is repeated until one candidate has more votes than the other remaining candidates put together. This candidate wins the election.

Supplementary Vote (SV)

Elections for mayors in England and Wales, and for Police and Crime Commissioners, use the Supplementary Vote system.

The SV system is like the AV system. Voters are limited to a first and second preference choice. A voter marks a cross in one column for their first preference candidate. They mark another cross in a second column for their second preference if they wish to do so.

If a candidate receives more than 50 per cent of the first preference votes then they are elected.

If no candidate reaches the 50 per cent threshold, the two candidates with the highest number of votes remain. This eliminates the other candidates. The second preference of the eliminated candidates are counted. Any made 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)

Single Transferable Vote is used for:

Elections for Deputy Speakers in the House of Commons

Northern Ireland Assembly elections

Local elections in Scotland and Northern Ireland

European Parliament elections in Northern Ireland.

Constituencies which elect more than one representative use STV.

Voters rank candidates in order of preference by marking 1, 2, 3 and so on. A voter can rank as many or as few candidates as they like or vote for only one candidate.

Each candidate needs to reach a quota. This is the minimum number of votes calculated according to the number of seats and votes cast.

The first preference votes for each candidate are added up. Candidates who achieve this quota are elected.

Surplus votes from candidates who hit the quota go to second preference candidates.

Votes from the candidate with the fewest first preference votes who do not achieve the quota are eliminated. Their votes go to the second preference.

Additional Member System (AMS)

The Additional Member System is used by:

the Scottish Parliament

the National Assembly for Wales

the London Assembly.

Voters are given two votes on separate ballot papers. One vote is for a constituency member and one vote is for a party list. In Scotland and Wales list members are elected by region. In London there is a single London-wide list.

Constituency votes are counted first and the members for each constituency are elected using first-past-the-post.

Additional members are then elected by counting the party list votes in each region. The number of members elected from the list is based on the percentage of the votes cast but also takes into account the number of constituency members already elected in the region. This is designed to make the result more proportional to the number of votes cast.

Closed Party List

The Closed Party List system is used by England, Scotland and Wales to elect Members of the European Parliament.

A voter marks a cross on the ballot paper next to the party's name. Parties get the number of seats in proportion to the votes it receives in each constituency.

Voters choose parties not candidates. The parties determine the order in which candidates appear on the list.