Supplementary vote

The supplementary vote (SV) is an electoral system used to elect a single winner, in which the voter ranks two of the candidates in order of preference. In an election, if no candidate receives an absolute majority of first-preference votes, then all but the two leading candidates are eliminated and there is a second count. In the second count, the votes of those who supported eliminated candidates are distributed among the two remaining candidates, so that one candidate achieves an absolute majority. It is a specific implementation of the contingent vote and instant-runoff voting. Under SV, voters express first- and second-ranked choices of candidate only, and, if no candidate receives an absolute majority of first-choice votes, all but the two leading candidates are eliminated. If a voter's first-choice candidate is eliminated but their second choice is one of the two remaining candidates, their vote is transferred to the second-choice candidate. The candidate with the most votes is the winner. This means that the winning candidate has the support of a majority of voters who expressed a preference among the top two, although not necessarily a majority of votes cast in the first count. The supplementary vote was used in all elections for directly elected mayors in England, including the Mayor of London, and in elections for police and crime commissioners, until 2022 when it was replaced by first-past-the-post voting (FPTP). In the early 1990s, the Plant Commission was established by the Labour Party to recommend a new voting system for the Parliament of the United Kingdom. When the Commission reported in 1993, instead of suggesting an already existing system, it recommended the Supplementary Vote system, which they said had never been used anywhere. (Apparently the commissioners did not know that a similar system, Contingent voting, had been in use in Australia as early as 1892.