The UK electoral system now decisively favours the Conservatives

Before the election, it was commonly assumed that the bias in the electoral system would favour Labour, as it has done since the 1990s. But Tim Smith illustrates how the skew on May 7 actually benefitted the Conservatives and contributed to their unexpected victory.

In the wake of the largely unexpected Conservative election victory, it was said that pollsters and political scientists had a lot of explaining to do after so many incorrect forecasts.  However, this author correctly predicted that the Liberal Democrats would do worse than was assumed , and also that the electoral system might well favour the Conservatives for the first time since 1987 which also turned out to be the case.  In this blog piece I will explain what has happened and the consequences for the next election.

At this election the two-party bias (or skew) in the electoral system moved from a pro-Labour bias of 54 seats, to a pro-Conservative bias of 48 seats, meaning that if the two parties had won the same number of votes, the Conservatives would have won 48 more seats than Labour.  The table below shows the decomposition of factors that result in this bias.  These can be obtained algebraically using Brookes’ decomposition method, as adapted by Johnston, Rossiter and Pattie. For a full explanation of the factors please read this piece on the Ballots & Bullets blog.

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