Effectively, as few as 8.73% of the total electorate could vote for a party to have a 1 seat majority in the House of Commons.
Data taken from:
This data has been simplified in the following ways:
- I have assumed 4 candidates per seat, or more accurately, the winning candidate to win 25% + 1 of the votes in their constituency. So the calculation is
((Avg Electorate * 0.7) * 0.25) + 1
- I have ignored where seats are not taken (speakers, Sinn Fein, etc).
- I have assumed 70% turnout, which is slightly above average from the past two elections, but not grossly so.
Based on this, to win 326 seats in the Commons, a party could achieve this from as little as 8.73% of the electorate voting for them, or 12.48% of all actual voters. This is very theoretical and does not represent the actual situation (where elections are actually decided only on marginal seats).
Even if we were to look at 100% turnout, it would only require 280,000 more votes.