It has been suggested that Labour should focus on the Green vote in marginal constituencies. What would happen if they succeeded?

Paul Mason, among others, has called for Labour to win voters back from the Green Party. In further conversation on Twitter, he has suggested that 18 seats were lost to Labour in 2015 because the ‘progressive vote’ was split by Green voters who Ed Miliband failed to woo. This figure was apparently taken from Fabian society research into potential 2020 target seats, though Mason intends to publish his own analysis of marginal seats soon.

Mason concedes that these wouldn’t be enough to make Labour Britain’s largest party again - the Tories are a hundred seats in front after all - but he suggests it could be decisive in removing a “de-facto Tory/Unionist majority.” So is that true?

To find out, I took the results from every constituency in the 2015 general election (data from Electoral Calculus), and imagined what would happen if Ed Miliband had won some or all of the Green vote. What would the outcome have been? (You can download a spreadsheet with all my results here, corrections welcome.)

First let’s put things in context. A party needs 323 seats to gain a majority in Parliament, after accounting for the Speaker and the absence of Sinn Fein. The Tories won the last election with 11.33 million votes, giving them 331 seats. Labour took 9.35 million votes, and 232 seats. The Greens were the 6th largest party by vote count, getting just a single seat from 1.16 million votes.

Adding the entire Green vote to Labour’s would have erased more than half the two million vote lead the Conservatives enjoyed, but that doesn’t necessarily translate into seat gains. So if we went through the data, constituency by constituency, and moved Green voters into the Labour column, what would happen?

Let’s start with something realistic. Labour’s collapse in Scotland saw them lose about 30% of their voters , down from just over a million in 2010 to roughly seven hundred thousand in 2015. Let’s imagine a similarly-seismic shift from the Greens to Labour across the country.

Seat changes if 30% of Green voters switched:

The results are not exactly dramatic. The Tories would lose just six seats, ultra-marginals like Derby North (with a Conservative majority of 41) and Gower (27). Labour would gain seven. With 325 seats, Cameron would still have formed a majority government and Labour will still be almost 100 seats behind, far out of contention.

Even we increase the vote grab to 50%, the Tories still lose only seven seats and still form a majority government. Remember that to achieve this, Labour would have to do something so radical that half of all Green voters switched sides, while not losing a single voter to any other party. And they’d still lose.



Seat changes if 50% of Green voters switched:

So clearly a hostile takeover of Green voters is fantasy politics, but what about an electoral pact? What if the Greens no longer contested elections against Labour, keeping only their seat in Brighton? A percentage of the Green vote would presumably swing to Labour. 50% would be a generous figure, but let’s go wild and pretend it’s 100% - that every single Green voter would happily switch to Labour. Do the Tories fall?

No. Let’s leave aside the absurdity of assuming that not a single Green voter would swing to the Lib Dems, UKIP, nationalist parties or elsewhere. Even if that were true, Labour would still only gain 11 seats, giving them 243. The Conservatives would still only lose 10 seats, falling to 321. While they might technically have been denied a majority in that scenario, making up the two missing seats would have been trivial.

Seat changes if 100% of Green voters switched (Excluding Brighton Pavillion):

There are other potential targets for a ‘Progressive Pact’ - Plymouth Moor View for example saw a combined Labour + Green vote of 16,017 versus a Tory vote of 16,020 - but to get there you have to somehow add more votes on top of a scenario that’s already completely implausible. Labour were already laser-focused on their key opponents in these constituencies, and the Green party could have contributed little with its own meagre resources.

All of this becomes irrelevant once you factor in the 2018 constituency boundary changes. These would reduce the Commons to 600 seats, with 298 needed for a majority. If the 2015 election were re-run with these new boundaries, Labour would have just 198 seats, with the Tories on 328. Any gains from a Green pact would be wiped out several times over.

And that’s all assuming that Labour can match their result in 2015, which looks unlikely. The Tories are now polling about 2-3 percentage points higher than their result at the 2015 election, and Labour are polling lower by a similar amount. If an election were held today, the likelihood is that the Conservatives would gain about 20 seats, and Labour would lose a similar amount. That shift would again make any Green pact irrelevant.

You may dispute these projections, but the broader point is that the number of scenarios which a pact with the Greens makes any difference to the result of an election is tiny. Unless the vote is astonishingly close to start with, half a dozen seats here or there just aren’t going to matter.

Green voters aren’t enough to topple a Conservative government, and they’re a barely-significant distraction for those aiming to create a progressive one... even if you could take every single one for granted.

