Brexit Podcast 28 May 2019

This page first posted 28 May 2019

1. Naive Projection

The Brexit party won the Euro elections with around 32pc of the vote, and the Conservatives were reduced to fifth place on 9pc. It is very tempting to ask what would be the result of a Westminster general election if those same figures were exactly repeated.

Party2017 Votes2017 SeatsPred VotesGainsLossesNet ChangePred Seats
CON 43.5%318 9.1%0318-3180
LAB 41.0%262 14.1%0181-18181
LIB 7.6%12 20.3%201+1931
UKIP 1.9%0 3.3%00+00
Green 1.7%1 12.1%00+01
SNP 3.1%35 3.6%210+2156
PlaidC 0.5%4 0.7%10+15
ChUK 0.0%0 3.4%00+00
Brexit 0.0%0 31.6%4580+458458
Minor 0.7%0 1.8%00+00
N.Ire 18 00+018

Prediction based on raw Euro election result.

This appears to indicate a massive landslide for the Brexit party with Nigel Farage returned as Prime Minister with an overwhelming majority.

But this is a bad guide to what may happen in a general election. Voting behaviour is very different at European elections than it is at general elections. A relevant example is UKIP, which won 27pc of the vote at the 2014 European elections, but got less than half that support at the general election in the following year. Back in 1989, the Greens won 14pc in the European elections, but failed to get more than 1pc at the next general election.

This projection is just a political fantasy, and is not realistic.

2. Realistic Projection

For a realistic projection we need to estimate how many voters have defected to the pro- and anti- Brexit parties to make a short-term protest and who will return to voting Conservative and Labour at the next general election. We can get this from polling, which shows that around half the people who voted for the Brexit and Green parties at the euro elections are "temporary supporters" who are likely to vote differently at a general election, whereas most Liberal Democrat voters appear to be permanent.

Looking at recent national polls in detail for both European and Westminster elections, and applying those differentials to the actual European results gives a more realistic estimate for Westminster party support. Those figures show Labour and the Conservatives tied on 22pc support each, with the Liberal Democrats on 19pc, Brexit party on 17pc and Green party on 8pc.

Using that projection to predict a general election gives this result:

Party2017 Votes2017 SeatsPred VotesGainsLossesNet ChangePred Seats
CON 43.5%318 22.3%366-63255
LAB 41.0%262 22.5%1624-8254
LIB 7.6%12 19.1%351+3446
UKIP 1.9%0 2.8%00+00
Green 1.7%1 8.0%00+01
SNP 3.1%35 3.9%210+2156
PlaidC 0.5%4 0.7%10+15
ChUK 0.0%0 2.3%00+00
Brexit 0.0%0 17.1%150+1515
Minor 0.7%0 1.3%00+00
N.Ire 18 00+018

Source: Poll of 14 polls from 3-21 May 2019, sampling 32,000 people, adjusted for measured pollsters' errors in predicting the EU election.

Within the margin of error it is not possible to say whether the Conservatives or Labour would have the more seats, but it could be very close. Each of the major parties is about 70 seats short of a majority, with the SNP winning 56 seats, the Lib Dems 46 and the Brexit party only winning 15.

Parliament would be quite hung, reflecting the divisions in the country.

These figures also show the forces on both major parties to move away from a centrist position on Brexit. The Conservatives have to attract many of the 17pc of the public who support the Brexit party. And Labour, conversely, has to attract many of the 27pc of people who support the Lib Dems and the Green party. If either Leavers or Remainers united themselves behind a single party, while the other side did not, then that united group would form a majority government.

This pushes the Conservatives in a Leave direction, whilst pushing Labour towards Remain.

3. Political Butterfly Effect

Of course, things can change as the public absorbs the results of the European election and as the Conservative leadership contest gets under way. A feature of the electoral system is that, in the current circumstances, a small change in public support can have a very large impact on the number of seats won.

The Conservatives are projected to be about 5pc ahead of the Brexit party, but win 240 more seats. But if this were to flip and the Brexit party was 5pc ahead of the Conservatives, then they could win about 115 seats more than the Conservatives.

The graph shows the seats won by the Conservatives and the Brexit party against the lead of the Conservatives over Brexit as a fraction of the popular vote (assuming all other parties hold steady).

Seats won by Conservative and Brexit parties against their vote difference

The dark blue line is the predicted number of seats won by the Conservatives. This starts from zero on the left-hand side and increases to an overall majority if the Conservatives get a lead of 17pc over the Brexit party.

The light blue line is the predicted number of seats won by the Brexit party. This is high when the Conservatives are low and vice versa. The Brexit party gets a majority if their lead over the Conservatives is more than 15pc.

The thin green line shows the total number of seats won by both parties. This dips quite low when the two parties have approximately equal popularity because the right-wing vote is split allowing Labour and other parties to win marginal seats.

If the two parties are equally popular, the Conservatives win 178 seats and Brexit wins 67 seats, but Labour wins 266 seats which is more than both of them together.

[Technical note: this isn't strictly the butterfly effect, which is the nickname for dynamical systems with sensitive dependence on initial conditions. But it is a situation with a very high degree of gearing where a small change in party support can lead to a big difference in seats, which is similar in spirit.]

4. Brexit outcome probabilities

Brexit is at peak uncertainty with the three main options all equally likely. Each of No Deal Brexit, an agreed Deal Brexit, and Remain are around 30pc in the political betting markets.

OutcomeProbability
No Deal Brexit in 201929pc
Meaningful vote to pass in 201926pc
Article 50 to be revoked30pc
Other (eg further extension)15pc

Source: Betfair Exchange (prices as at 27 may 2019, 12:45).

Physicists call this maximum entropy when all the possible states have the same probability and it also occurs at the heat death of the universe.

5. Conservative leadership candidates

We also looked at evidence for the popularity of some candidates for Conservative leadership. Four sources were considered:

Although there are many candidates, the table shows the top four front-runners, as measured by their chance of winning.

CandidateWin chanceName recognitionNet Good
(CON GE voters)
Net Good
(Brexit EU voters)
Boris Johnson34%93%-13%+13%
Dominic Raab21%58%-27%-27%
Michael Gove16%79%-31%-33%
Jeremy Hunt7%85%-24%-42%

Sources: Win chance from Betfair Exchange (as at 27 May 2019 12:45); Name recognition from Hanbury Strategy poll, 9-13 May 2019, sample size 2,000; Net Goods from Com Res poll for Daily Telegraph, 10-12 May 2019, sample size 2,028

Of the top four candidates, Boris Johnson is the punters' favourite and also scores the best for name recognition, least worst among Conservative supporters, and best among Brexit party voters. Jeremy Hunt is second best for name recognition and popularity among Conservative supporters. Dominic Raab is second best for chance of winning and appeal to Brexit party voters. Michael Gove scores moderately in all categories, but is less popular with Conservative supporters.

More polling on the merits of these and other candidates will undoubtedly be conducted in the coming weeks, so these figures may well change before the outcome is settled.


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