Polling-based modelling produced exclusively for the Guardian shows that replacing first-past-the-post (FPTP) with various forms of proportional representation would produce markedly different distributions of seats in the UK parliament.
Under the current FPTP arrangements, the modelling indicates Labour could finish with 250 seats, leaving the party short of an overall parliamentary majority. By contrast, proportional systems in the same model generally reduce the number of seats awarded to the largest party and increase representation for smaller parties, producing a more balanced chamber that more closely reflects vote shares.
How the systems differ
First-past-the-post converts votes into a winner-takes-all outcome in individual constituencies, a mechanism that can amplify the seat share of the largest party. Proportional systems allocate seats with the stated aim of matching the composition of the legislature more closely to the proportion of votes each party receives. The modelling applies recent national polling to these different translation rules to illustrate how seat totals would change.
Local results and implications
The Guardian’s accompanying visualisations let readers view the modelled outcomes at constituency and area level, showing where shifts between systems would have the biggest effect. Those maps and tables underline that under proportional arrangements, many more parties are likely to hold seats and no single party would necessarily command an outright majority as often as under FPTP.
The analysis does not prescribe a particular system but highlights the trade-offs involved: FPTP can produce clear single-party governments, while proportional systems tend to deliver legislatures that more closely mirror the electorate’s overall preferences, often requiring coalitions or agreements among parties to form stable administrations.