Methodology

Majority, margin and swing

A constituency’s majority is the winner’s votes minus the runner-up’s; we also show it as a share of valid votes. A party’s overall majority in the House of Commons is its seats minus all other seats combined.

Swing is Butler swing: the average of one party’s gain in vote share and the other party’s loss, in percentage points (half of party B’s change minus party A’s change). Conservative–Labour swing is positive towards Labour and negative towards the Conservatives.

Turnout

Turnout is valid votes as a share of the electorate, as the House of Commons Library defines it. Unopposed seats are left out of national turnout.

Seats changing hands

For 2010 and 2024 a gain is measured against the Library’s notional results on the new boundaries. For 2015, 2017 and 2019 it is measured against the previous election. Before 2010 we mark a gain only where the constituency had the same name and the same boundaries at the previous election; seats on new boundaries are not marked.

Constituency histories

Constituency pages follow a name over time. Boundaries usually changed at each review (1945, 1950, 1955, 1974, 1983, 1997, 2005 in Scotland, 2010 and 2024), so the area behind a name can differ between elections.

Swing calculator

The swing calculator applies uniform national swing: the change you set for each party is added to its share in every constituency in Great Britain, shares are kept at zero or above, and the highest share wins. Northern Ireland seats keep their actual winners. It is a teaching tool, not a forecast.

People’s Vote and polls

The People’s Vote and other polls are open website polls. Anyone can respond, respondents choose themselves, and the results are not weighted. They are not representative of any population and are not a prediction. A nation or region’s split is shown only once it has enough responses (set in the admin), and responses are limited by browser, account and network to reduce repeat voting, which can never be fully prevented.