Here’s how many seats Reform UK, the Greens and the SNP would win under every UK voting system in 2026
Key Points
- More in Common modelled UK seat outcomes under four voting systems for the Guardian
- Reform UK would take 46% of seats off 28% of the vote under First Past the Post, falling to 28% of seats under a regional party list
- The Greens would gain 770% more seats under a proportional list system; the SNP would lose more than half
- Labour and Conservative seat numbers change only slightly across all systems
- Every proportional system leaves only a progressive coalition or a Reform-Conservative coalition as routes to government
New modelling from More in Common for the Guardian shows Reform UK would lose almost 40% of its seats under a proportional voting system, while the Greens would gain 770%.
The research firm ran the projections using its MRP model, putting a set of additional questions to voters alongside its standard voting-intention question and asking how they would cast a ballot under each hypothetical system.
The exercise covers First Past the Post, regional party list, the additional member system and single transferable vote.
What each system delivers
The current First Past the Post system converts Reform UK’s support into by far the largest seat premium of any arrangement tested. The projections put the party on:
- 46% of seats off 28% of the vote under First Past the Post
- 33% of seats off 28% of the vote under the additional member system
- 28% of seats off 28% of the vote under a regional party list
- 27% of seats off 26% of the vote under single transferable vote
Under First Past the Post, that seat haul would leave Reform within reach of a sizeable coalition should the Conservatives lend their support. The three proportional systems strip out the bonus almost entirely, with the regional list producing a seat share that matches the party’s vote share exactly.
The Greens and the SNP move in opposite directions
A purely proportional list system removes the tactical calculation that shapes voting under the current arrangement, because backing the candidate seen to be winning locally carries no advantage. That change hits the two parties whose current seat counts depend most heavily on geography.
The SNP would lose more than half of its seats, because the concentrated Scottish vote that delivers constituencies under First Past the Post stops paying a premium.
The Greens would move the other way. Their support spreads too widely across the country to win many seats under the current system, and a proportional count would raise their seat number by 770%.
Labour and the Conservatives barely move
One of the most noable findings in the modelling concerns the two parties that built the current system.
Labour and the Conservative fortunes change only slightly across all four voting systems, which indicates that neither party still counts as a principal beneficiary of First Past the Post.
Every system tested produces the same broad outcome at Westminster.
Under each of the proportional arrangements, only two routes to government exist: a progressive coalition drawing on some combination of Labour, the Liberal Democrats, the Greens, the SNP and Plaid Cymru, or a coalition of Reform UK and the Conservatives.
That result cuts against the central argument for First Past the Post. The system is meant to manufacture clear majorities and stable governments, yet More in Common’s latest MRP already projects a hung parliament under the current rules, with Reform UK 30 seats short of a majority.
More in Common has flagged the limits of the exercise. The modelling cannot predict how parties would campaign under different rules, or which parties might fragment, merge or emerge in response to a more proportional system.
