- Supplementary Vote (SV) is an electoral system used for elections with one winner. It is focused on ensuring that the winning candidate has a majority or broad suport.
- Used in: London mayoral elections (until 2024), police commissioner elections in England and Wales.
- Voters have two choices: a first preference and a second preference candidate.
- If a candidate receives more than 50% of the first preference votes, they win outright.
- If no one gets a majority, everyone except the top two candidates are eliminated. Second preference votes for the remaining two are then added to their totals to decide the winner.
- SV aims to ensure the winner has broad support, while keeping the voting process simple.
| Advantages | Disadvantages |
|---|---|
| Ensures the winner has wider support than under FPTP, more legitimacy | Not a proportional system as smaller parties are still disadvantaged |
| Relatively simple for voters to understand and use | Many second preferences may not be counted if both top candidates were not chosen |
| Reduces the likelihood of "wasted" votes | Can encourage tactical voting |
| Encourages candidates to seek support from a larger audience | Does not guarantee majority support if turnout is low |
- SV is designed for single-winner elections and aims to combine simplicity with a broader mandate for the winner.