Supplementary Vote

With the Supplementary Vote (SV), candidates have to campaign to get a broader base of support.

Supplementary Vote

The Supplementary Vote (SV) was used for electing Mayors and Police and Crime Commissioners in the UK.

It part of a broad group of ‘preferential’ voting systems, which include the Alternative Vote used in Australia and the Contingent Vote used to elect the Sri Lankan President.

How to vote with the Supplementary Vote

There are two columns of boxes alongside the candidates’ names on the ballot paper. One column of boxes is for voters to mark their favourite candidate with an X and one in which to mark a second favourite with an X. Voters don’t have to mark a second favourite if they do not have one. Voters can put a X in both boxes for one candidate but this is effectively the same as just marking your favourite and no additional benefit comes from this.

How the Supplementary Vote is counted

With the Supplementary Vote, if no candidate gets over 50% of the vote, the top two candidates continue to a run-off and all other candidates are eliminated. When casting their ballot voters can put a second choice (who they would vote for in a runoff) on the original ballot paper.

If your favourite candidate gets through, your vote is counted for them in the run-off. If they didn’t, but your second choice did, your vote goes to them. The run-off candidate with the most votes is declared the winner.

Benefits of the Supplementary Vote

As voters mark two Xs rather than writing a number to show their first and second choice, it is simpler for the voter when they are also using other electoral systems that use Xs, such the Additional Member System for the London Assembly or local councils using First Past the Post.

The Supplementary Vote means politicians need a wider base of support than First Past the Post, but they are much less likely to get half the vote than with the Alternative Vote. SV is viewed as encouraging a more positive style of campaigning as candidates desire the second preferences of third parties.

Supporters argue that first and second choices are more firmly held than say the difference between a fifth and sixth choice.

"The Supplementary Vote stops candidates winning on low levels of support, but doesn't need them to get half the vote"

Electoral Reform Society

As the Supplementary Vote only lets voters express two choices, it is possible for a high number of voters’ first choices to be excluded in round one and for their second choice to not be in round two. In almost two decades of Supplementary Vote elections for the Mayor of London, only in 2016 has a mayor won more than 50% of the total ballots once these ‘non-transferable’ ballots are included.

The 2021 London Mayoral Election

As the top two in the first count (as seen on the left), Shaun Bailey and Sadiq Khan go through to the second round (on the right). The remaining candidates are excluded and people who voted for them have their votes moved to their second choice. If their second choice was Shaun or Sadiq these votes are added to the totals to find the winner.

In 2021 the number of signatures needed to stand was reduced due to the pandemic, resulting in a large number of independent candidates. The most logical thing to do is to cast your first choice for your genuine favourite candidate, and your second choice for your preferred candidate out of the two that you think will reach the second round.

Although deciding on just a first and second choice is simpler for the voter than putting all the candidates in order (as you could with the Alternative Vote), this becomes more difficult as the number of candidates increases and it is not obvious which will be in the top two.