A voter can prefer one party nationally and vote for another candidate locally because they believe that candidate has a better chance of defeating an opponent. The decision depends on both preference and a view of the constituency contest.
Tactical voting concerns the reason for a choice. A switch between parties is not automatically tactical, and election totals alone cannot establish why an individual voted as they did.
Why the voting system creates the incentive
Under First Past the Post, only the candidate with the most votes wins. A supporter of a trailing candidate may therefore consider backing a more competitive alternative.
In an illustrative contest, A has 38%, B 35% and C 20%, with the remaining 7% elsewhere. A transfer of four points from C to B would change the winner. That arithmetic describes a possible redistribution, not a prediction that C’s voters would agree to it.
Some might prefer A to B, some might continue backing C and some might abstain. Adding party totals together treats these different people as an automatic voting bloc, which the results do not justify.
Preference, switching and tactical intent
A voter who comes to prefer a different party and votes for it has changed allegiance. A voter who continues to prefer their original party but backs another to influence the result is making a different kind of choice.
Survey questions can investigate these motivations, but wording and timing matter. Asking for a preferred party, a constituency vote and the reason for that vote can supply different information.
The British Election Study’s post-election research illustrates how panel evidence can trace changes in individual choices. National party totals, by themselves, cannot identify the flows between parties or the motives behind them.
Which candidate is best placed?
The previous election is a useful starting point, provided the boundaries match. It becomes less decisive when political support has changed substantially, a candidate has left, an independent has entered or a party has mounted a stronger local campaign.
Current constituency polling or MRP estimates can add evidence, but both have limitations. A projected two-point lead should not be treated as a settled ranking. Check the model’s methods and uncertainty.
Campaign leaflets are interested evidence. A bar chart should identify its election, geography and source. A local council ward, an opinion poll and a parliamentary constituency result are not interchangeable baselines for the same claim.
What can polling questions capture?
YouGov describes asking respondents specifically about their constituency as part of its voting-intention process. That gives respondents room to take local competition into account; it does not prove that every such answer will be acted on or classify every tactical voter.
Different question designs help explain why pollsters can disagree. The actual parties and candidates standing also matter, especially before nominations are settled.
Why tactical recommendations can conflict
Different services may use different fieldwork, models, assumptions or political objectives. One may recommend the best-placed challenger according to a historic result; another may favour a different candidate in a current projection.
A credible recommendation needs a clear objective and inspectable evidence. It should acknowledge a genuinely uncertain contest rather than turn a small estimated difference into a confident instruction.
UKDecides provides constituency information and explains the evidence without endorsing a tactical choice. Readers can inspect the local result, winning margin and source material, then judge the claims being made.
Sources and further reading
- UK Parliament: constituency winners under FPTP
- YouGov: constituency voting questions
- British Election Study: post-election evidence on party switching
Reviewed 7 October 2026. Worked examples are illustrative unless an election or poll is identified.