Supplementary Vote

The Supplementary Vote (SV) is the system used for electing mayors and Police and Crime Commissioners in the UK. However, the Elections Act 2022 introduced to the House of Commons in July 2021, and receiving Royal Assent on 28 April 2022 changes the voting systems to FPTP for mayors and PCCs. (2022 Elections Act )

Labour has claimed these changes to electoral law make it easier for Conservatives to win future mayoral elections, 11 of the 13 posts being contested across England are held by Labour. Prof Tony Travers, of the London School of Economics, said “It’s likely that first past the post would make it somewhat easier for the Conservatives to win if they could come up with a really good candidate,” Labour’s Sadiq Khan won the London mayoral contest comfortably against his Conservative rival, Shaun Bailey, once voters’ second preferences were taken into account. But Khan beat Bailey by only 40% to 35% on first preference votes, as some leftwing former Labour voters shifted to the Greens and other smaller parties. Travers said Labour faced the joint challenge of finding a message that lets them take on the Conservatives at a national level while also stopping leftwing voters in major cities moving to the Greens. “We’re back to the usual problem of the fragmentation of the left, while the centre-right vote is much better at holding itself together,” he said.

There is also evidence that voters are confused by the use of the supplementary vote system. Almost 5% of ballots cast in this year’s mayor of London election were rejected, mainly because voters had voted for too many candidates.

Operation 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.

Where is it used?

· Elections for the London Mayor and other elected mayors; Police and Crime Commissioners in England and Wales However, the Elections Act 2022 introduced to the House of Commons in July 2021, and receiving Royal Assent on 28 April 2022 changes the voting systems to FPTP for mayors and PCCs (The Act introduces voter photo identification for in-person voting to the United Kingdom for the first time)


Voters are given two choices, first and second.

If a candidate wins more than 50% of first-choice votes, he or she is elected. If not, all candidates drop out except the top two in the voting. Second preferences are added to first preferences and the winner now achieves a majority.

The AV system is not used, except for some by-elections in Scotland and Northern Ireland. It was rejected in the 2011 referendum on electoral reform.

The country is divided into constituencies, as under first-past-the-post. Each constituency returns one winner as MP.

Voters place all candidates in order of preference. (Voters do not have to vote for all candidates, but only as many as they wish.)

If one candidate wins more than 50% of first-preference votes, he or she is elected.

If no candidate achieves an overall majority of first choices, the lowest placed candidate is eliminated. His or her second-choice votes are distributed to the other candidates.

This process continues until one candidate has an overall majority.


The system ensures that the winner has an overall majority. It ensures fairness because all voters have two choices and so can potentially affect the outcome

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.


· It ensures broad support for the winner. Sadiq Khan, elected Mayor of London in May 2016, has the largest personal mandate of any elected politician in British history (see Table 1.4).

· It is simple and straightforward to use.

· It has allowed some independent candidates to win; for example 12 out of 40 Police and Crime Commissioners were independents in the 2012 contest, although the number fell in the second elections in 2016.


· SV is not proportional as one individual is being elected to a single office.

· The winner does not need to get an absolute majority of the votes cast.

· Voters need to be able to identify the likely top two candidates in order to have influence over the outcome, and this is not always clear (with the exception of London).

It is generally believed that there would be a relatively little change from first-past-the­post. However, it is assumed that the Liberal Democrats would gain some seats at the expense of both main parties. Small parties would gain little if anything. Voters would have a greater choice and not need to vote tactically.