How an Anti-Brexit Alliance (or Pro-Brexit Alliance) would change the General Election arithmetic

LibDems gain Brecon and Radnorshire from Conservatives with 1,425 vote majority on 12.0% swing
LibDems gain Brecon and Radnorshire from Conservatives with 1,425 vote majority on 12.0% swing
Result of the by-election in Brecon and Radnorshire by-election

On Thursday, the Liberal Democrats took the seat of Brecon and Radnorshire in a by-election. Chris Davies, the former Conservative MP who was recalled after claiming false expenses, saw his 8038 vote majority disappear as Jane Dodds, the new Liberal Democrat MP, took the seat with a majority of 1425 votes. Much of the credit for this was the decision of two other pro-Remain parties (Green and Plaid Cymru) deciding not to put forward a candidate, and instead to back the LibDems, while the pro-Brexit vote was split between three different candidates.

Of course, the interesting question now is to what extent this can be repeated across the country in a general election scenario.

Projection: CON 300–327, LAB 207–233, SNP 42–52, LD 34–48, PC 3–6, BREX 0–8, GRN 1–2, OTH 19–20
Projection: CON 300–327, LAB 207–233, SNP 42–52, LD 34–48, PC 3–6, BREX 0–8, GRN 1–2, OTH 19–20
Base scenario, based on current polling

Thanks in part to Boris Johnson’s appointment as Prime Minister, this has been a rich week for political polling. Averaging polls over the last week shows the Conservatives close to their 2017 result, with the SNP and LibDems making the most gains at Labour’s expense. The implication is a 1/8 likelihood of the Conservatives getting a majority of seats in the House of Commons, and an 80% likelihood of the Conservatives, Democratic Unionist Party, and Brexit Party having a majority between them.

It is this scenario against which we will be comparing the possible alliances.

For this scenario, we will define an anti-Brexit alliance to involve the Liberal Democrats, Green Party, Plaid Cymru, and Scottish National Party. Such an alliance would most likely pick the party that’s most likely to win in the constituency. We cannot assume that all voters of one party would support another, so the margin of error has to be widened accordingly.

Projection: CON 279–308, LAB 196–222, LD 52–70, SNP 49–54, PC 7–15, BREX 0–7, GRN 1–4, OTH 19–20
Projection: CON 279–308, LAB 196–222, LD 52–70, SNP 49–54, PC 7–15, BREX 0–7, GRN 1–4, OTH 19–20
If an Anti-Brexit Alliance nominated a single candidate in each constituency

This approach would give the alliance approximately 32 additional seats, twice as many at the Conservatives’ expense than at Labour’s. While this wouldn’t bring them anywhere close to forming a government, it would reduce the likelihood of a combined majority of Conservative, DUP and Brexit Party from 80% to just 2%. On the other hand, on a 95% probability, they would have enough seats to back a Labour government if it were intent on delivering a second referendum on Brexit.

One of the messages from Brecon and Randorshire was from the Brexit Party to the Conservatives: deliver a proper Brexit or we’ll make your electoral lives miserable. But what if the Tories were able to convince the Brexit Party to back their candidates instead of putting up their own?

Projection: CON 395–422, LAB 136–161, SNP 38–49, LD 20–31, PC 2–6, GRN 1, OTH 19
Projection: CON 395–422, LAB 136–161, SNP 38–49, LD 20–31, PC 2–6, GRN 1, OTH 19
If the Brexit Party encouraged their supporters to vote Conservative

If all Brexit Party supporters voted Conservative, this would be enough for them to pick up around 90 seats, cementing a Commons majority of well over 100 over all other parties. (Sound familiar, Mrs. May?) Of course, this must be heavily caveated. Around 1/4 of Brexit Party supporters voted Labour in 2017, so we can’t assume they’d all move to the Tories. There’s also the question of how much supporters would trust the Prime Minister’s strategy on Brexit, and whether they would come out, stay home, or vote for someone else (such as UKIP). At worst, though, the Tories would certainly have an overall majority, and most likely one that is large enough to overcome any backbench rebellion.

The Anti-Brexit Alliance, as we defined it earlier, would not be enough to overcome any decision the Brexit Party may make to back the Conservatives. The only way this could be overcome is if Labour were able to become part of this Anti-Brexit Alliance. But would they be able to convince the other participants to stand aside for them? Probably not.

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I am Joe. I am a techy at heart, a self-taught psephologist (political number cruncher), a pleasure cyclist, and someone who just calls things as he sees them.

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