The numbers turning out for Jeremy Corbyn during the leadership election has been a surprise that no-one predicted. But, it’s fine speaking to the converted (those who have made the effort to come out to events) but will that translate into electoral success?

Many Corbynites are claiming that this surge in support (much of which is from people previously disengaged from politics) will result in increased turnout and more people voting Labour. Ten weeks ago claiming a strong leftwing agenda would result in increased voter turnout might have been dismissed as fanciful, but given the advent of Corbyn-mania this scenario is clearly plausible (but not proven).

A while back I did an analysis of the general election results. Seeing as I have the data I thought it might be useful to play around with it to see if increased voter turnout could have an impact on the 2020 general election.

Below is a model you can play with to see the different results. But before you play with the model here are a few facts to bear in mind with respect to the model.

The turnout in the 2015 general election was 66.1 per cent. You can find the general election turnouts since 1945 here and you’ll see that turnout was only above 80 per cent twice: 83.9 per cent in 1950 and 82.6 in 1951. So my model has assumed a Corbyn led Labour Party can get turnout up to a plausible 75 per cent in every constituency, which is a large increase of nearly 10 per cent on 2015. But you can change this if you want to. Remember the largest change in turnout since 1945 was in 1974 when turnout went up from 72 per cent in 1970 to 78.8 per cent in 1974, and this was the time of huge political turmoil with the Miners’ Strikes, so a 10 per cent increase in turnout would be a record. It would be wrong to assume all the new voters because of increased turnout would vote Labour, some would be motivated to vote Tory to “stop Corbyn.” So I have assumed 85 per cent of new voters would vote Labour. Again you can change this if you wish. A Corbyn-led Labour Party would undoubtedly bring some disgruntled lefties who voted Green back to Labour. I have assumed 75 per cent of Green voters would switch to Labour. But not all will, as Green voting is clearly an expression of identity. You can change this figure on the model if you disagree with my assumption. My model only looks at seats in England and Wales as Scotland as things are very different due to issues around nationalism. There is no doubt a Corby-led anti-austerity Labour Party would win back many voters in Scotland, but nationalism is a strong force in Scotland, so it would be fanciful to assume all seats would be won back. I’ve assumed Labour would win 25 seats. But again you can change this if you want as the model allows. I have assumed all other votes remain the same. It is unlikely a Corbyn-led Labour Party would win many votes back from the Tories, but it could win votes from working class UKIP voters. Equally some UKIP voters may return to the Tories to stop a Corbyn-led Labour Party. Given the Tories are the main opponents for Labour assuming other votes remain the same seems reasonable for the moment. Finally, this is based on the 2015 boundaries and the Tories intend to reduce the number of seats from 650 to 600 and they will seek to get boundaries redrawn in such a way that it benefits them. So whatever the results this model shows, it will be harder for Labour if the boundaries are redrawn.

And now, on to the model. See below. Enter your values in the red boxes and the graph will change.

If you want to use it on a phone or tablet you need to double tap one of the red cells to get it to bring up the keyboard.

What are your conclusions? Mine are that if a Corbyn-led Labour Party increased turnout significantly and engaged with non voters, it is certainly plausible that Labour could be the largest party and could form a minority government, or maybe have a supply an confidence arrangement with the SNP, Greens and Plaid Cymru.

So, the Tories clearly could be ousted but it is going to need a lot of effort to get those non voters out: they are called non voters for a reason. And, even if turnout can be increased by nearly 10 per cent it seems very unlikely a Labour majority government could be formed. But then again given the pounding Labour took at the last election maybe it is too much to expect a majority Labour government in 2020 whoever is the leader.

Then again the 2020 general election is more than fours years away – a lot can happen and some of the assumptions in this model may seem very wrong by then. But this is at least a start at looking at the possible impact on turnout.