UKIP as a spoiling factor, part II

Following on from yesterday’s post on whether or not the presence of UKIP had cost the Conservative party a number of seats…

cim has done some analysis suggesting that a UKIP candidate produces a net increase in turnout of about 2.5% – 1,000 votes. However, the average UKIP candidate took around 1,600 votes, suggesting that they’re only taking around 40% of their votes from other candidates and the remainder from potential abstainees. If about half of that 40% would have voted Conservative, and the remainder voted for another minor party if one was present, then we can find the seats where the Conservative candidate was less than 20% of the UKIP vote away from beating their opponent.

There’s six of them – albeit one by a mere four votes, so we can perhaps call Dudley North a 50-50 chance.


If we raise the defection rate to 30%, we still have the same six seats under the threshold; if it’s raised to 40% – indicating that all defectors to UKIP came from the Conservatives – they would recover a seventh seat, Great Grimsby, from Labour.

Six seats is not enough to produce a definite majority, of course – but it’s certainly a non-trivial number, especially since they would come directly from the opposition. Had they taken these six seats, we’d be looking at 311 for the Conservatives versus 301 for an opposing Lib Dem-Labour coalition; it would become substantially harder for a reasonably robust coalition to form against the Conservatives, and so they would have a better chance at gambling on a minority government.

Historically speaking, it’s a plausible number. The Referendum Party (remember them?) in 1997 took 2.6% of the votes, and are estimated to have cost the Tories about four seats. UKIP took 3.1% of the vote this time around, so six seats is well within the bounds of plausibility.

2 thoughts on “UKIP as a spoiling factor, part II”

  1. I had another thought on this. We should be able to determine how many votes UKIP takes from the Conservatives by comparing seats with a UKIP candidate to seats without. In theory, if UKIP takes votes away from Conservatives, then the Conservative percentage of the vote in a seat they win (or lose) by a given margin should be slightly lower. – i.e. in non-UKIP seats where the Conservatives had 33% of the vote, Labour would need 33.1% to beat them, but if UKIP takes 1% off the Conservative vote, Labour would only need 32.1% to beat them, so in seats with a 0.1% margin against the Conservatives, you’d expect the Conservatives to have on average +1% of the vote in non-UKIP seats, for the same margin of victory.

    So, after excluding seats where there were other significant contenders or no Conservatives (Scotland, Wales, Northern Ireland, Brighton Pavilion, Buckingham) and then excluding seats where the Conservatives were in third…

    Nothing. The distributions are virtually identical, and in so far as there’s a difference, the Conservatives actually seem to gain a tiny number of votes in seats with a UKIP candidate, and Labour lose about the same amount (but really, the trendlines are so close that I don’t think it’s significant in either case)

    That would suggest that insofar as UKIP are stealing votes and not just boosting the turnout, they’re stealing them from the major parties roughly proportional to the vote those parties would have had anyway, and so haven’t actually changed any seats over.

    (This in some ways makes sense – while a Conservative voter might be closer to the rest of UKIP’s platform, a Labour or Lib Dem voter would have much more incentive to vote UKIP as an anti-EU protest vote)

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