What is tactical voting in a by-election?
Tactical voting means choosing a candidate other than your sincere first preference because you believe another vote is more likely to affect the outcome. Under First Past the Post, where only the first-placed candidate wins, voters may judge that their preferred candidate cannot win and instead support the best-placed candidate who can defeat the party they like least.
FPTP rewards finishing first and only first. When voters believe their preferred party cannot win in a particular constituency, some may switch to a second-choice candidate who has a better chance of winning — or, more precisely, of defeating the candidate they most want to lose. By-elections, with their intense media focus and clear two-horse-race narratives, can encourage this behaviour.
How it works under FPTP
- Only the first-placed candidate wins representation — second place wins nothing.
- Voters may judge that their preferred candidate cannot realistically win in this constituency.
- They may therefore support the best-placed candidate capable of defeating a less preferred opponent.
What tactical voting is not
It is important to distinguish tactical voting from related but different phenomena:
- Tactical campaigning — where parties concentrate resources in winnable seats. This is a party strategy, not a voter decision.
- Electoral pacts — where parties formally or informally agree not to stand against each other. This removes a choice from the ballot rather than changing how voters use it.
- Genuine persuasion — where a voter sincerely changes their preference. This is a change of mind, not a strategic calculation.
Why by-elections encourage tactical voting
Several features of by-elections make tactical voting more likely. There is only one contest, so all attention is focused on one result. Polling and previous results receive intense scrutiny, giving voters clearer information about who can realistically win. Opposition supporters may see a rare chance to coordinate behind a single challenger.
Limitations and uncertainties
Constituency polling can be sparse or unreliable. Campaigns have strong incentives to claim they are the main challenger — the famous Liberal Democrat bar chart is a deliberate tactical-voting tool. Voters may reject tactical appeals on principle. And local party strength may differ significantly from what previous results suggest, particularly after boundary changes or demographic shifts.
In a constituency where Party A holds the seat with 40%, Party B has 30% and Party C has 20%, Party C supporters face a decision. If they believe Party C cannot win, some may vote for Party B to defeat Party A. But this depends on Party C supporters preferring Party B to Party A — which is not guaranteed — and on their believing Party B is genuinely competitive.
Tactical voting cannot be confidently identified from aggregate results alone. Surveys and voter reports are normally needed to establish individual motives.
The simulation includes a tactical-voting mechanic that can shift vote shares when the gap between the top two candidates narrows. Students should ask: what information would voters need in real life before coordinating effectively? The simulation compresses this process; in reality, tactical voting depends on imperfect information and individual judgment.