Resolves at the party that the first prime minister elected after the next general election is from.
1,000I find it interesting that the bookies have the odds very different to Manifold: https://www.oddschecker.com/politics/british-politics/next-uk-general-election/most-seats
E.G. at the time of this comment, Reform are at 29% on Manifold, and several bookies have them at 5/6 (~54.5%).
(Note that the question is slightly different: "Next UK General Election - Most Seats" vs. "Which party will the Prime Minister after the next UK general election be from?". Generally, the PM is from the party with the most seats, but it could be different.)
@AlexMennen that was my first thought as well, but I'm not sure. If Reform are the largest party, it seems quite likely that Reform plus Conservative will have a majority of seats. A year or two ago I couldn't have imagined the Tories being a junior partner in a coalition with Reform, but now I could see it. I can't really see much difference between Badenoch/Jenrick and Farage these days.