The 2019 Election result using different voting systems

Using polling from YouGov for this report, the Electoral Reform Society has projected the results of the 2019 election in Great Britain under three other electoral systems: Party List Proportional Representation (List PR), the Additional Member System (AMS), and the Single Transferable Vote (STV)

How would different voting systems have changed the result in the 2019 General


Conservative 365 288 284 312

Labour 203 216 188 221

Liberal Democrat 11 70 79 59

Scottish National Party 48 28 26 30

Plaid Cymru 4 4 5 5

Green Party 1 12 38 2

Brexit Party 0 11 12 3

Party List Proportional Representation (List PR) is one of the most commonly used electoral systems around the world. List PR systems vary depending on whether voters cast their vote for a party (closed list) or can vote for their preferred candidate within a list (open list). Between 1999 and 2019, closed List PR was used in Great Britain to elect members of the European Parliament (MEPs). The projection shows that the Conservatives would still have been the largest party in the House of Commons with 288 seats, which is in line with their having received a plurality of votes at the election. But, based on the model, they would not have gained an overall majority. Conversely, parties with a less geographically concentrated support base would have obtained seats more in proportion to their share of the vote.

List PR systems score highly in terms of proportionality, but – especially in the closed list variant – they limit voter choice, because electors are forced to vote for a list pre-determined by a party and cannot nuance their choice by ranking candidates, as in preferential systems. Though the open list variant can increase voter choice, there is often a weaker constituency link in List PR systems as voters elect a slate of candidates from a larger area than under other electoral systems.

The 2019 Result projected using List PR (change shown in red)

Conservative 288 -77

Labour 216 +13

Liberal Democrat 70 +59

Scottish National Party 28 -20

Green Party 12 +11

Brexit Party 11 +11

Plaid Cymru 4 0

The Additional Member System (AMS) – also known as Mixed Member Proportional Representation (MMP) outside of the UK – is a hybrid voting system. It combines elements of First Past the Post (FPTP), where voters choose one candidate to represent their constituency, and Party List Proportional Representation. In AMS elections, voters choose a constituency candidate (elected under FPTP) and have a second vote for their preferred party. Each party will publish a list of candidates in advance. Voters can cast both votes for the same party or vote for different parties in their constituency and regional ballots. List seats are then allocated to parties on a proportional basis, usually applying some form of electoral threshold (generally 5%)

List seats ‘top up’ and partially compensate for the disproportionality associated with the FPTP element of the system, by taking into account how many constituency seats have already been won by a party. For example, if a region has 10 seats (five constituency seats and five list seats), and a party wins half the list votes and three constituency seats, then it should win an additional two list seats to reach ~50 percent vote share it received. The design of AMS systems can differ quite considerably. One significant difference is the ratio of constituency to list seats, which has consequences on the proportionality of this voting system. While the Scottish and Welsh versions of AMS are quite similar to each other, especially when compared to those used in Germany or New Zealand, they differ with regards to the proportion of constituency and list MPs. In Scotland, the proportion of ‘top-up’ list MPs is much higher than in Wales (43.4% compared with 33.3%), which means that the Scottish version of AMS returns a more proportional parliament. In our modelling, we have opted for a 50:50 ratio of constituency to list seats, which leads to a much more proportional outcome than the versions of AMS used in Scotland and Wales. We also applied a five percent electoral threshold.

Given the relatively high proportion of list seats, this AMS projection delivers a broadly proportional result, with seats more closely matching how people voted at the 2019 election. The Conservatives, Labour and the SNP all lose seats in this projection, while smaller parties benefit considerably from the list seats. AMS is often considered to be a compromise system, as it combines the constituency link of FPTP with the proportionality of list PR. As shown above, with a higher percentage of list seats, it can typically produce relatively proportional results, but has the same problems of safe seats and wasted votes as FPTP. Further, as AMS uses closed party lists, parties still have a lot of control over who gets elected. Voters who particularly dislike a candidate at the top of their preferred party’s list, or like a candidate from a party they otherwise do not support, are unable to express this at the polling station. Voter choice thus remains constrained – though compensated by fairer representation than under FPTP

Projected result of 2019 Election using AMS

  • Conservative 284 -81

  • Labour 188 -15

  • Liberal Democrat 79 +68

  • Green Party 38 +37

  • Scottish National Party 26 -22

  • Brexit Party 12 +12

  • Plaid Cymru 5 +1

The Single Transferable Vote (STV) is a form of proportional representation which uses preferential voting in small, multi-member constituencies of around three to six MPs. It is used in Northern Ireland for all non-Westminster elections, Scottish local elections, the Republic of Ireland, Malta and the Australian Senate. STV maintains a constituency link and strong representation, while enhancing voter choice and leading to much more proportional outcomes than FPTP. Under STV, each voter has one vote, but they can rank candidates in order of preference. Voters vote by putting a ‘1’ next to the name of their favoured candidate, a ‘2’ next to the name of their next favoured candidate, and so on. Voters can rank as many or as few candidates as they like. If a voter’s preferred candidate has no chance of being elected or has enough votes already, their vote is transferred to another candidate according to their preferences. STV ensures that very few votes are ignored when compared with FPTP. It also ensures maximum voter choice, as electors can rank their choices both within and between parties and independents. As a slate of MPs is elected from a slightly larger area than under FPTP, STV also keeps the constituency link while ensuring that the diversity of opinion in the country is fairly represented in parliament.

This STV projection shows a result that is more proportional and more in line with how people voted at the 2019 general election, with no party gaining an overall majority of seats. Based on our STV projection, the Conservative Party secures 312 MPs (49.4% of all GB MPs), just shy of a majority of seats in the House of Commons and more in line with their percentage of the vote in Great Britain (44.7%). Though Labour and the Conservatives slightly outperform their vote share in terms of seats under STV, smaller parties’ seat share in our model is much more similar to how people actually voted at the election, with the Liberal Democrats making significant gains in our projection (an additional 48 MPs, leading them to have 9.3% of seats on 11.8% of the vote). As previously stated, smaller parties would have campaigned very differently in an actual STV election.

Projection 2019 Election Result using STV

  • Conservative 312 -53

  • Labour 221 +18

  • Liberal Democrat 59 +48

  • Scottish National Party 30 -18

  • Plaid Cymru 5 +1

  • Brexit Party 3 +3

  • Green Party 2 +1