Would the Brexit party win a majority of 240 seats at a general election?

“As you know the Brexit Party won the European elections by a very substantial margin… If the first past the post had been used, we would have a parliamentary majority of over 240 seats.”

Nigel Farage, 7 June 2019

Last Friday, Brexit Party leader Nigel Farage and chairman Richard Tice delivered a letter to the Prime Minister stating their belief that some Brexit party MEPs should become part of the government’s Brexit negotiating team.

In the letter they say that if the EU election results had been repeated at a general election, then the Brexit Party would win a majority of 240 seats.

This is a reasonable enough estimate to make, in theory, based on the best available evidence. However it’s very unlikely, in practice, that the Brexit party would win so many seats at a general election. EU election results can’t be used as a proxy for how people would vote in a general election.

How the figure is calculated

The Brexit Party won 31.6% of votes cast in Great Britain in the recent EU parliamentary elections. We don’t know exactly how the Brexit party converted that figure into the number of seats it would win in at a general election, and have asked it for more information.

But one possibility is that they took the share of the vote won by each of the major parties, and ran them through the Electoral Calculus website.

Applying those vote shares to the constituencies of the 2017 general election, the website estimates that the Brexit party would win 446 seats—a majority of 242 seats overall.

This would be a landslide for the Brexit Party, wiping the Conservatives off the electoral map entirely, so they’re left with no seats at all. Labour would have an estimated 93 seats, the SNP 56, and the Liberal Democrats 31.

The Electoral Calculus website is widely respected, and Martin Baxter, its founder and CEO, told us they use regression techniques to estimate the geographic spread of support for each party, and how this translates into seats won under the first past the post system. That said, it is, of course, an estimate based on modelling techniques, and no model is perfect. Many of these seats are also predicted to be marginals—meaning they estimate that it would be close-run between at least two parties.

Professor Chris Hanretty, a political scientist at Royal Holloway University, produced a separate estimate of how the EU election vote shares would play out in a general election result. He too modelled a Brexit Party landslide (albeit a slightly smaller one), with the party probably winning 414 seats—a majority of 178.

This vote share is very unlikely to come about at a general election

However, Professor Hanretty emphasises in his analysis that the EU parliamentary election results tell us “almost nothing” about what would happen at a general election.

He goes on: “I estimate that the Brexit party won the most votes in over four hundred Westminster constituencies. The Brexit Party will not win four hundred seats in a future general election.”

Martin Baxter, who runs Electoral Calculus, also told us it’s very unlikely that the EU election results would be repeated at a general election.

People don’t necessarily vote the same way in EU elections as they do in a general election. For example, UKIP won 34% of the vote in Great Britain in the 2014 EU parliamentary elections, but only 13% of the vote in the UK-wide general election the following year.

Turnout at the EU parliamentary elections was 37%, whereas general elections normally see a turnout of at least 60%. A much higher number of voters could well affect the results.

People also might cast their vote based on different issues at a general election compared to an EU one. Polling by Lord Ashcroft shows that Brexit policy was the second-most important reason why voters supported the Brexit party and the most important reason why voters supported the Lib Dems (who between them received over 50% of votes).

Priorities might differ in a general election.  Polling on voting intention at a general elections shows support for the Conservatives and Labour at about 20-30% each in the last month or so (whereas they won 9% and 14% respectively in the EU parliamentary elections). The Brexit party has consistently been polling around 18-26% in the same period, and the Liberal Democrats around 10-20% in most cases.