I count 306 seats where Labour are 1st and the Conservatives 2nd, or Conservatives 1st and Labour 2nd.
In the other 326 seats, either the Lib Dems, Reform, Greens, SNP, Plaid Cymru or independents are a top two party. Where most voters live, the traditional Labour vs Conservative debate is no longer the relevant one.
On Merseyside the Greens are second in the majority of constituencies, the Tories are often fifth. It's been like that for a while I think.
The 99 seats where the Lib Dems are top-two are the really interesting ones here because a) most of these seats are now ones they actually hold rather than ones where they're runners up, and b) their main challenger in these (typically middle-class Southern) seats is almost always the Tories. The Lib Dems winning 72 seats this time is an enormous part of why the Tories had a record-breaking bad night as opposed to just a regular bad one, and their ability to sustain this next time will be key to keeping the Tories out of government in future.
For the other parties (e.g. Greens are top-two in 43, mostly in big cities; Reform in 103, mostly white working-class Brexit areas), they're almost always the runner-up party (usually by quite a big margin) behind Labour.
I mean, the FPTP system is fucked – that aside... For your stat to be right, wouldn't you have to calculate it also in terms of the number of constituents to a given constituency? E.g., Constituency A has 10 constituents, Constituency B has 15 constituents, and Constituency C has 100 constituents; both A + B have a non-Lab/Cons party in first or second place; C has Lab first and Cons second. In that scenario, it wouldn't be true that "most people" live in a constituency where Lab or Cons are not both 1st or 2nd (where A-C is exhaustive).
I don't know how that would extrapolate to the real constituencies with their varying population/electorate figures. Certainly, it's a very uneven and strange system at present, which allows for all sorts of gerrymandering. But only given the sum of 20 constituencies (per your calculation) where Lab/Cons are not the top two, I don't think you can infer the situation for most people.
In any case: fuck this system, PR soon please.
One of the key elements of the boundary reform that went through between the 2019 and 2023 elections was to ensure that constituencies have broadly equal numbers of electors. Prior to this there had been more variation (and a few big anomalies), whereas the boundary reform means that all seats now have an electorate of 73,393 +/-5%. (I think this was a pretty uncontroversial change but had been held up for years because the Tories kept trying to accompany it with a change to the number of MPs, which was a lot more controversial.)
I haven't bothered doing the calculation on a seat-by-seat basis, but the electorate distribution would have to skew really badly in favour of the +5%s being Lab/Con and the -5%s being non-Lab/Con for your concern to come to fruition.
