Supplementary Vote (SV)

In the Supplementary Vote (SV) system voters rank their two favoured candidates on the ballot paper in order of preference, therefore nominating only a ‘first’ and a ‘second’ choice by marking a cross in each of the two columns aligned next to the list of candidates. For a candidate to win outright following the first round of voting, he or she must gain over 50% of the first preference votes. If no candidate achieves this, all but the top two candidates are eliminated from the race and their second preference votes are reallocated; the candidate with the highest total resulting from this is therefore elected.

Supplementary Vote is a majoritarian system. It has been used in the UK since 2000 for electing the London Mayor, and as of May 2015, sixteen council areas across England have a directly elected executive mayor. SV is suitable for stand-alone elections where a single executive figure must emerge as a unifying figure and in this case the system confers legitimacy on the winner by demonstrating their ability to attract support from across the capital city; it also tends to reward candidates who lean towards the centre ground. With first and second preferences combined, Sadiq Khan can claim 56.8% of the London electorate, a significantly more impressive share than the 36.1% won by David Cameron in 2015. Supplementary Vote was introduced as part of the Labour government’s democratising reforms, following the decentralisation and decline in the status of London government seen under previous Conservative administrations.

Advantages of the Supplementary Vote

The winning candidate must have secured wide-ranging support; they need not win the first ballot nor will they often have an initial majority of over 50%, but they will need at least some support from across the spectrum to then win the election following the addition of second preference ballots. Unlike AV, where there is no such restriction on second preferences, the London mayoral rules state that only second preference votes granted to one of the top two candidates on the first ballot are then filtered back through the system, so smaller or more extreme parties cannot boost their performance in this way and if a voter opts for an extreme party as a first preference and a mainstream candidate as a second preference, for example, it is only the second of these votes that will count. Also, there is only one round of tallying and the process is a little easier to follow than AV, where a candidate might conceivably come third in the first ballot and emerge the winner after several rounds of reallocating second preferences.

Disadvantages of the Supplementary Vote

An absolute majority of votes cast is not required to win and if SV was used to elect an assembly or legislature there would be no guarantee that the governing party would have over 50% of the votes. The seats vary in size and turnout can range widely between constituencies, some of which are more marginal than others. Crucially, SV is not a proportional system so the problem of fairness and representation remains; it is rejected by many advocates of electoral reform for this reason.

As with the simple plurality system, SV does quickly reduce a potentially large field of candidates down to a choice between two parties; first ballot votes cast for small parties are significant only for the second preferences attached to them and this is a disincentive to voters. Turnout in the London mayoral elections has always fallen significantly below that of UK General Elections: 45.3% in 2016 matched the turnout in 2008, when Boris Johnson stood for the first time, but the three remaining London elections (2000, 2004 & 2012) saw turnout range between 34.4% and 38.1%. FPTP is not thought significantly better but it does seem to have broader public support and a greater ability to secure participation, although this might owe more to the primary nature of General Elections compared to more limited regional settings.

A more nuanced approach to voting is possible, as outlined above, but this risks attendant problems. A tactical vote, whereby a favourite candidate is awarded a first vote and a pragmatic choice is made at the second preference stage, is that it is not always clear which two candidates will contest the second round. Admittedly in each of the five mayoral elections to date it has been a straightforward two-horse race; the highest third-place finish was 15.3% for Liberal Democrat candidate Simon Hughes in 2004. However, there is no guarantee that this would always be the case and in a more closely contested election the pragmatic course of action might not be clear, leading to a possible distortion of outcomes.

Comparison of SV with FPTP 

Supplementary Vote follows the same principle as the ‘Alternative Vote’ system, of which it is a variant, and can be used to elect representatives in single-member constituencies, one similarity it shares with FPTP. Although the system does ensure, through reallocation, a majority of over 50% for the winner, it is common that the winner will not have an absolute majority of first preferences and there is also a chance that an initial majority in the popular vote will be overturned, as can sometimes happen with the overall outcome under FPTP. Technically, the process of voting is different as two votes are cast, although there is a similarity in that each party may only propose one candidate, and the voter has no say over the selection of these candidates. As with FPTP, a large number of parties do stand for election under this system but there is a similar bias towards the larger parties and only these candidates have a realistic chance of success. Also, it is virtually impossible for a smaller party to win the election and the victor under SV is more likely to be a compromise candidate than under FPTP, which for some presents a transparency problem.