How many seats could UKIP have under a different voting system?

“UKIP should have a massive amount of representation in Parliament. If there was proportional representation, they would have 100 seats or so”

BBC Question Time audience member, 17 November 2016

UKIP would have a lot more seats in the House of Commons if the UK had an electoral system that links votes to seats more closely. It realised just one MP from the party’s 3.9 million votes at the 2015 election.

If the system were perfectly proportional, that 12.4% of the vote would give UKIP 12.4% of MPs—around 80 out of 650 in total.

The Electoral Reform Society, which campaigns for a change from the current ‘first past the post’ system, estimates that UKIP would have won 80 seats under a ‘list PR’ system, 54 under a ‘single transferable vote’ regime, and stayed at one using the ‘alternative vote’ that was rejected at a 2011 referendum.

We don’t know exactly how people would have voted if a different system was in place, and the actual votes cast don’t tell you about people’s second preferences.

These proportional systems involve selecting more than one preference, whereas in the general election people could only vote for one party. The different electoral scenarios were put together by conducting a survey of people’s party preferences just after the election.