Electoral systems

On this page you will find discussion and analysis of electoral systems. The content here is specifically designed for A level politics and early undergraduate level students looking to deepen their understanding of the topic. At A level specifically, the component 1 topic on ‘electoral systems’ is where this topic will most apply. 

Click on any of the questions below to be taken to the answer.

What are electoral systems?

Why do types of electoral systems matter?

What different electoral systems are used for elections in the UK?

What is First-Past-the-Post?

Why is First-Past-the-Post criticised?

If first-Past-the-Post is unfair, why hasn’t it been replaced?

What is proportional representation?

What is the Single Transferable Vote system and how does it work? 

What is the Additional Member system and is it a proportional system?

What is the Supplementary Vote and is it proportional?

Is the Supplementary Vote working in London?


Further reading

What are electoral systems? 

An electoral (or voting) system is the process through which the electorate – those eligible to vote in a particular election – choose who they want to represent them. The video below explains more about what electoral systems are and why they’re important.

What are electoral systems and why do they matter?

Why do types of electoral systems matter?

Electoral systems are crucial to the way in which people take part in politics, and who holds power in a representative democracy. The electoral system determines how a fundamental political right – the right to vote – is exercised. The way in which votes are cast and counted impacts the composition of the democratic chamber, the manner in which representatives relate to the public, and which party, or group of parties, is able to form a government. The type of electoral system used can influence the choices individuals make when casting their vote(s), as well as the kind of government that can be formed. Electoral systems therefore play a defining role in the character of the political system.

According to Channel 4 News, this is how seats would have been allocated in 2019 if the party list system had been used (a form of proportional representation). 

What different electoral systems are used for elections in the UK?

First-Past-the-Post (with a long history, but imposed uniformly as the system for UK parliamentary elections across the board since the Representation of the People Act 1948)

Single Transferable Vote (first used in special university constituencies at Westminster elections from 1918, and for Northern Irish parliamentary elections from 1919)

Additional Member System (first used in elections to the Scottish Parliament and Welsh Assembly in 1999) 

Supplementary Vote (first used for London Mayoral elections in 2000) 

What is First-Past-the-Post?

First-Past-the-Post (also referred to as the Single Member Plurality system) is the system used for UK parliamentary elections. It has been used in every Westminster constituency since the 1950 election, and was widely employed long before that point. Each voter can vote for one candidate from the list of candidates standing in their constituency. The candidate who gets the most votes wins, and is elected to be the Member of Parliament for that constituency. It is what is often referred to as a ‘majoritarian’ (as opposed to ‘proportional’) electoral system. This means that the seat is won outright by a candidate (rather than distributed in relation to the proportion of votes cast). The winning candidate does not actually need to win an outright majority of votes cast, however, simply at least one more than any other candidate (or a ‘plurality’).

 The BBC explains how FPTP works for UK general elections. 

Why is First-Past-the-Post criticised?

First-Past-the-Post (FPTP) has had its critics since the nineteenth century. A range of different arguments are raised against the system. 

One of the main criticisms of FPTP is that it is disproportionate. On this account, an electoral system should make sure that a party’s level of support is reflected in the number of seats they win. FPTP, however, does not produce a distribution of seats that reflects the overall way in which votes have been cast across the country. Parties that receive less than half of the total UK vote regularly win a majority of seats in the House of Commons. Detractors say this means that under FPTP the legislative chamber fails to reflect and represent the public’s political preferences and awards unearned majorities to one of two main parties (since 1918, the Conservatives and Labour). 

The 2015 election illustrates how disproportionate the system is, with UKIP winning 12.6% of the vote but securing just 1 MP. The SNP on the other hand won 4.7% of the popular vote but secured 56 seats (Source: Daily Mail).

Another part of this criticism of FPTP is that, while it rewards the two main parties, it disadvantages some smaller parties and candidates. Parties like the Brexit Party (now known as Reform UK), Green Party or the Liberal Democrats, might pick up a significant percentage of votes cast. But because these are spread across many constituencies, none (or very few) of which they are likely to receive the most votes in, they may end up winning much fewer seats than their vote share suggests (or potentially none at all). This is said to be unfair to these smaller parties, depriving them of a realistic chance of winning seats despite modest levels of national support. 

Caroline Lucas of the Green Party explains why FPTP harms smaller parties like hers during a Westminster Hall debate on electoral reform.

FPTP is also said to suppress potential levels of support for these parties, as people may opt to vote instead for a larger party that has a better chance of winning, even if they do not best reflect their political views. People, in such accounts, end up voting for the candidate they dislike the least or voting tactically rather than out of genuine support. Through this, FPTP leads to and preserves the dominance of two main parties at the expense of smaller political forces. 

Two-party dominance also means that the main parties have to be broad, encompassing a spectrum of political views. Whilst some say this is a positive, meaning that they have to rely on support from across the electorate; others say it means that parties end up fighting endless internal battles, with different factions vying for control but never able to break away and form a new party. 

Taken together, it is argued that all of this can lead people to become disillusioned with the political process. This in turn may cause people to feel that voting is pointless and to stop participating in elections altogether.  

FPTP also has an issue with so-called safe seats. In some areas, a particular party has won for many generations – making the party assume the seat is a safe win. This means that parties end up paying little attention to these places, focusing instead on the marginal seats they need to win to secure a majority. Elections end up focusing on the issues that concern these marginal constituencies rather than those that are of wider importance. 

Others make more practical criticisms of FPTP. They suggest that it does not bring the benefits that its proponents claim. For example, it is often said that FPTP produces stable, single party governments, typically with large majorities in Parliament. However, a series of recent elections (2010, 2015, 2017) have shown that this is not always the case. Furthermore, it does not necessarily even reward the party with the most votes with the most seats, failing to do so at general elections in 1951 and February 1974. 

C.G.P. Grey explains how FPTP works and the problems it creates.

If First-Past-the-Post is unfair, why hasn’t it been replaced?

Although there has been significant opposition to FPTP over many years, it remains the system that is used for UK Parliamentary elections. Why is this? One obvious reason is that if FPTP helps one of two main parties to get elected at each election, then neither of these parties have an incentive to get rid of it. FPTP often produces a majority for a particular party in Parliament, meaning they can form a single-party government on less than a majority of the overall vote. It is hard to see why this party, now in government, would change the system to make it more likely that at the next election they would lose power, or have to form a coalition government with a smaller party. 

There are other reasons FPTP for Westminster elections has not been replaced. To start, there is disagreement on what electoral system should replace it and a number of possible models to choose from. In 2011, there was a referendum to replace FPTP with a system called the Alternative Vote (AV), which was unsuccessful. Although there are some significant differences, AV is a majoritarian system like FPTP rather than a proportional system. Some proponents of changing the electoral system, who would have preferred a proportional model, therefore found it difficult to support the Yes to AV side in the campaign. 

Others would say that we still have FPTP because it is the best system for UK Parliamentary elections. They argue that the most important feature of an electoral system is not whether it produces a Parliament that most accurately reflects the political attitudes of the electorate, but whether it produces an effective government that voters can hold to account. As we have seen, proponents of FPTP say that it produces single-party, majority governments which can carry through a distinct political agenda more effectively than coalition or minority governments. Voters are given a clear choice of government – typically one of the two main parties – who they can then vote out of office at the next election if they don’t deliver. Supporters of FPTP propose that this is preferable to confusing and ever-changing coalition and minority governments that may manage to cling on to power with the support of smaller parties, despite being rejected by the voters. 

What is proportional representation?

Proportional representation refers to a range of voting systems that aim to produce a distribution of representation in the democratic assembly that reflects the way the electorate has voted. For example, in a perfectly proportional system a party that received 25 per cent of the votes would get 25 per cent of the seats. Of the electoral systems mentioned above, the Single Transferable Vote system and, to a certain extent, the Additional Member System fall into this category. 

What is the Single Transferable Vote system and how does it work? 

The Single Transferable Vote (STV) is a proportional electoral system used primarily in the UK in Northern Ireland. STV is often said to be more complicated than some other voting systems. However, it produces a high degree of proportionality whilst also maintaining a strong connection between representatives and their local area. 

Under STV, multiple representatives are elected to each constituency (unlike FPTP). So, one area may be choosing four members, for example. Voters rank candidates in order of preference. A quota of votes that a candidate has to reach in order to be elected is determined by dividing the total number of votes by the number of seats available. If a candidate receives more votes than the quota they are elected, and their additional votes are redistributed to the other candidates on the basis of who was put as the next preference. If this process doesn’t fill all the available seats, then the candidate with the least votes is eliminated and their votes are redistributed to whoever their voters put as their second preference. This process is repeated until all the seats in the constituency have been filled. 

C.G.P. Grey looks at how STV works.

Proponents of STV say that it allows voters to vote for who they really want, rather than tactically or for the least bad option. They can vote for candidates all from the same party or for individuals from a number of different parties or independent candidates. Furthermore, it is said that constituency boundaries under STV are more in keeping with recognisable town, city, or county distinctions than a system like FPTP, where artificial boundaries are drawn based on population density. However, others argue that STV is complex and less easy to comprehend than FPTP. Nevertheless, its use in the Republic of Ireland, Northern Ireland and for some elections in Scotland indicates that voters are able to get to grips with STV and use the system effectively. 

This video explains how STV votes are counted.

What is the Additional Member system and is it a proportional system?

The Additional Member System (AMS) is used in the UK for elections to the Scottish Parliament, the Welsh Assembly and the Greater London Assembly. It is intended to mix aspects of FPTP and proportional representation – it is neither wholly proportional nor wholly majoritarian. Its proponents claim it forms a hybrid of the two types of system that combines their advantages and avoids their disadvantages.  

Electors are asked to cast votes for two types of representative. They cast one vote for a constituency candidate under the FPTP system, where the constituency candidate with the most votes wins. They also cast a vote for a party list in a wider election, covering a particular region, and for which multiple representatives are elected. The seats for these larger, multi-member districts are distributed so that the overall number of seats the party gets for that region (including the FPTP constituencies) is as proportional as possible to the percentage of votes the party received for their list. 

The ‘party list’ electoral system is a form of proportional representation. When the UK was a member of the European Union, it was used in Great Britain to elect members to the European Parliament. Each party presents a list of candidates for a particular district, for which several representatives will be elected. Each voter casts a vote for the list of their preferred party and the seats for the district are distributed proportionally to the number of votes each party list received.  In the AMS system this is combined with the use of FPTP for the constituency seats.  

C.G.P. Grey explains how the Additional Member System works.

Many point to Scotland and Wales, where the Scottish National Party and the Labour Party have been in government for a long period, to demonstrate that AMS can produce stable governments, with close to a single-party majority, whilst also producing a legislative chamber that is more proportional to voters’ choices than under FPTP. However, critics argue that the system can be gamed in certain ways, for example through tactically splitting votes and voting for one party in the constituency election and another, smaller party in the list election. Others say that AMS creates two tiers of MPs, given that constituency MPs often have responsibilities that party-list MPs do not.

This video from the BBC explains how AMS works in Scotland’s parliamentary elections.

Further reading: David Klemperer, ‘A gameable electoral system? The Additional Member System in Scotland’

What is the Supplementary Vote and is it proportional?

The Supplementary Vote (SV) is the system used for electing mayors and Police and Crime Commissioners in the UK. It is what is referred to as a preferential voting system: voters give a first preference and a second preference. In this sense, it is similar to the Alternative Vote (AV) system, which was the subject of the 2011 referendum. However, under the AV system, voters can rank as many candidates as they like. If once all the votes are counted a candidate has secured an overall majority, then they are elected. However, if no candidate secures over 50 per cent, then under SV all the candidates other than the top two are eliminated. The second preferences of those who voted for an eliminated candidate are then distributed between the top two. Whoever has the most votes in total after this process is elected. 

SV is not a proportional electoral system. However, it is said to be an improvement on FPTP in that candidates cannot win outright with low levels of support. It is a system which is designed to produce overall majorities for a candidate, something which is not required under FPTP. Critics say that SV continues to maintain two-party dominance, as only two candidates can get through the first round – usually the two biggest, most well-known parties. Votes for smaller parties are only relevant in relation to whether their second preference is for one of the two larger parties that has made it through to the second round. Ballots where both the first and second preference are for small parties will usually be wasted and not count towards the final result.   

This video from Simple Politics explains how SV works.

Is the Supplementary Vote working in London?

SV has been used for London Mayoral elections since 2000. The two main parties – Conservative and Labour – still dominate these elections. However, it is argued that SV means that candidates for these parties have to try and develop a broad level of support, as they are also competing for second preference votes and so have to appeal to a broad range of voters. It is said that this gives smaller parties more sway around elections, as the big parties will be keen to be picked second by their voters. 


Click here for a PowerPoint on electoral systems that condenses the information above. The PowerPoint is primarily designed for teachers covering the topic.

Further reading:

David Klemperer, Electoral Systems and Electoral Reform in Historical Perspective

David Klemperer, The Electoral System and British Politics

Nat le Roux, ‘Labour and the electoral system: The myth of defeat and the chimera of victory’

Neil Kinnock speaks with the Constitution Society, ‘FPTP is fundamentally flawed’