Votes that determine elections Votes that determine elections

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People often speculate about the number of votes that actually made the difference in any given election. In other words, the minimum number of net votes that needed to be cast for the opposition in sufficient seats to produce a different result. This number, in comparison to the total electorate, is quite small.

For each election, apart from February 1974, the Key Votes are calculated as the summation of half the majority, rounded up to the next whole integer, in the smallest number of the most marginal seats that would have made the difference. Comparisons between elections don't make much sense because of complications such as boundary changes. The calculation of the government majority excludes the Speaker.

YearGovtMajorityNo of Seats to
reverse the result
Key VotesElectorate% of
2005Lab71 ¶3616,43444,245,9390.0371
1992Con21 11 1,24143,249,7210.0028
1979Con4423 7,89941,091,2600.0192
1974 OctLab4330640,101,2650.0008
1974 FebLab-3217>3,67739,769,3210.0092§
1970Con3116 3,28639,398,5180.0083
1966Lab9749 37,58935,964,9980.1045
1964Lab5 34235,882,5270.0001

§ votes in non-Labour marginal seats required to give Labour a majority

 This figure, unlike that for previous years, assumes that the Speaker and three Deputy Speakers (who do not normally vote) are excluded, along with the 5 Sinn Féin MPs (who did not take up their seats)


Votes that determine elections

Political Science Resources
© Richard Kimber
Last Modified: 22 Oct 12