Contingent vote

For this reason, the term instant-runoff voting has also been used for this method,[citation needed] though this conflicts with the more common meaning.

[2] The supplementary vote was used to pick directly elected mayors and police and crime commissioners in England prior to 2022.

[2] In an election held using the contingent vote, the voters rank the list of candidates in order of preference.

In the second round, the votes of the voters whose first preference had been eliminated are transferred to whichever of the two remaining candidates they ranked the highest.

This means that if a voter's marked preferences do not include either of the candidates who survive to the second round, then it will be impossible to transfer the vote, which is therefore declared "wasted" or "exhausted".

[3] However, in the 2024 presidential election, the strong third-party candidacy of Anura Kumara Dissanayake, who won 42% of the first preference vote, forced a second round of counting for the first time in the nation's history.

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.

[2] Although some commentators credit the head of the commission, Raymond Plant, with the invention of SV, according to others, it was the brainchild of a Labour member of Parliament (MP) at the time, Dale Campbell-Savours and academic Patrick Dunleavy, who outlined and advocated for it in an article for the New Statesman magazine that was published September 29, 1989.

In the 2021 London election, a record 5 percent of ballots were wholly rejected, and no candidate achieved a majority of the vote.

[8] The government responded by ending the use of the supplementary vote in 2022,[9] citing voter confusion with a complex system.

These positive effects are moderated by the incentives SV creates for voting, in some circumstances, for only candidates from among the leading three.

Political scientists Colin Rallings and Michael Thrasher noted two flaws of SV:[14] Under the two-round system (also known as runoff voting and the second ballot) voters vote for only a single candidate, rather than ranking candidates in order of preference.

It also guarantees that every voter has a chance to express a preference between the top two, unlike the limited forms of contingent vote.