Which party would benefit most if everyone voted in the UK general election?

Question

Every time there is a general election acquaintances tell me they won't vote because their vote won't make any difference (or words to that effect). I have long since given up trying to argue with them, but I'm curious to know which party would benefit if the non-voters could be bothered to vote.

Do we have any evidence, for example from polls, of how the landscape would change if everyone voted?

I realise there are people who are genuinely uninterested in how the country is run and I guess we should exclude this group as their votes would be effectively random. So a refinement to the question could be what proportion of the non-voters would vote if it were made trivially easy and how this sub-group's votes would affect the outcome?

Answer 1

Short answer, the Liberal Democrat and generic "other" vote (i.e. Reform/Green/Party you didn't know was running) would go up a bit, and Labour would get a better vote share, but it's plausible it wouldn't normally matter to the winning party.

Obviously any attempt an answer to this is limited by many of the usual factors surrounding opinion polls and elections, including:

• the fact that people lie about their voting intentions (or change their minds at the polls)
• that people vote in the competition which is happening, not a hypothetical competition and
• compulsory voting (e.g in Australia) appears to correlate to significant numbers of spoiled ballots (although the voting system probably plays a role here).

Notwithstanding that, many major polling companies do ask a question on likelihood to vote (e.g. on a 0-10 scale) and provide cross-tables with voting intention for at least the three biggest parties, e.g. here for a recent YouGov poll or here for tables from Survation with a more detailed breakdown. On average, these tend to show those who are certain not to vote don't really vote for any of the likely winners, but that Conservative voters do show a slightly firmer intent than potential Labour voters, and those tending Liberal Democrat are less firm than either. This correlates with the observation of Tory voters being on average older and in better paying jobs, both of which have been demonstrated to vote more often than an arbitrary person.

Now we have to ask, would it matter? In the 2024 election, likely not, since Labour is on course to win big regardless. What about historically? There is one confounding factor; Labour historically win seats with a lower turnout than Conservative wins (see e.g. page 69 of this report for 2015), so it's plausible that a significant (and hard to gauge) portion of the difference would often run up the score in Labour safe seats. Overall, I would argue it would lead to a slightly increased systematic bias against large Conservative parliamentary majorities, with evidence it might the Lib Dems and Greens a few more seats, or in this election allow Reform to take some victories.

Answer 2

The fact that the U.K. has single member district plurality voting and that political party is not homogeneous nationally, also means that in the great many districts where the outcome isn't close that their vote really doesn't matter. And, even if their vote did matter in an individual constituency, there might not be enough of them to change which party controls parliament. The 2019 data is available to crunch here.

Only 32 out of 652 winners had a victory margin of under 1,000 votes and the Tories won 38 seats over a majority.

A shift of at least 1,235 votes in each constituency, typically over 2% of the votes validly cast, would have been necessary to change the result and force the Tories into some sort of coalition or minority government.

The median margin of victory was 11,127 votes. Lots of people are in constituencies where their vote doesn't matter and that is one reason that turnout isn't higher.

This is also a feature of the system as much as it is a bug.

Constituencies that aren't close aren't prone to having an official result that differs from the one counted due to election administration issues or election fraud or just dirty tricks in campaigning. The less close the marginal seat necessary for the winning party or coalition to win is, the more stable the results are against any flaw in the election process.

Clear election results are particularly important in a system like that of the U.K. that doesn't have many outside checks and balances to resolve election disputes, and few institutions that can provide a backup second best way to run the country while uncertainties in the election results are resolved.