How Different Electoral Systems Would Have Impacted the UK Election

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Result of the UK election using First Past The Post

The UK election is now over, and after the Conservatves’ strong victory, Brenda from Bristol needn’t worry about, well, another one. But what if we weren’t using First Past The Post in this country? As ever after an election, we’ll take a look at what could have happened under other electoral systems.

The UK held a referendum in 2011 about switching to this ranked-ballot system, and the UK voted by a 2–1 margin against switching to it. Under this system, a candidate requires 50% of the vote in their constituency to get elected, and if no candidate gets to 50%, then the last place candidate is eliminated and their vote gets redistributed to the next highest preference.

Of course, it’s worth reminding everyone that the assumption that 100% of voters of one party would preference another has never been backed up by polling evidence. On this occasion, I couldn’t find any polls which asked about second choices; the closest I could find was a Savanta Comres poll which asked about tactical voting, and for lack of any better figures, I’m using this question as a proxy.

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Estimated result of UK election using Alternative Vote
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The border colour indicates the party winning the seat under First Past The Post. The fill colour indicates the party winning the seat under Alternative Vote.

When it comes to the new Labour-Conservative marginals, the question of who would take them under AV would come down to who came in third place. In many leave-voting areas, the Brexit Party’s preferences would have been enough to give them another ten seats, though they would lose six that they won in remain-voting areas as preferences there would go against the Conservatives. Overall, Labour would be down nine seats under AV, while the Conservatives would be up four, the Liberal Democrats up three, and the Scottish National Party up two seats.

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Estimated election results using Proportional Representation

Using the d’Hondt method for allocating seats within each region, we see that the Conservatives would have finished significantly short of an overall majority in the House of Commons. Labour would be up fractionally compared to First Past The Post, while the Liberal Democrats would have gained seats rather than lost them. Meanwhile, the Brexit Party would pick up 11 seats, eight of which in the north of England, and the SNP’s seat count would undermine the party’s assertion that the vote constituted a mandate for a second referendum. In Northern Ireland, there would be more unionist MPs than nationalist MPs, unlike what happened under First Past The Post.

Single Transferable Vote is a ranked ballot system used for multi-seat constituencies, and is used for most elections in Ireland. For this scenario, I devised 169 constituencies, each containing either three, four or five seats, with a candidate’s goal to surpass either 1/4, 1/5 or 1/6 of the vote (respectively) to get elected, with any excess votes going to the next preference on the ballot paper. The aim is that the seats would be split proportionally within each constituency.

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Estimated election results using Single Transferable Vote

Despite the result being roughly proportional within each constituency, parties with a high concentration of voters will still do better than parties whose votes are spread out. Under STV, the Conservatives would finish just short of a majority, but if they combine with the Brexit Party and one of the two unionist parties in Northern Ireland (and count on Sinn Féin continuing their abstentionist policy), that would be enough to give them a bare majority.

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Seat-by-seat estimate for Single Transferable Vote

Given the strong Conservative majority, it’s difficult to see any chance of electoral reform getting anywhere near passing through Parliament. But supporters of smaller parties, on both the Leave and Remain side of the Brexit debate, will continue to call for an end to First Past The Post.

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I am Joe. I am a techy at heart, a self-taught psephologist (political number cruncher), a pleasure cyclist, and someone who just calls things as he sees them.

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