A second referendum has been suggested by the Liberal Democrats (amongst others) as one way to resolve “Brexit” and its related complications. While it may offer an attractive escape from difficult negotiations with EU democrats — it’s actually far more than that. With every passing day a second referendum becomes closer and closer to a democratic necessity. This may appear a bold claim in isolation, but the reasoning behind it is logical and can be statistically demonstrated using simple population data.

In 2016 there was a demographic divide in the result of the referendum. Broadly, young people voted Remain, with approximately three quarters of 18 to 24-year olds voting to stay in the EU (see reference A). Conversely, older people voted Leave, with only about one third of people over 65 voting to stay in the EU (reference A).

This split has strong implications for the future based on two key population effects. The first is that new voters are constantly entering the voting population. As young people turn 18, they become of voting age and (crucially) they are statistically far more likely to vote Remain (see reference D). Secondly, voters are constantly exiting the voting population due to death — an event far more common amongst older voters who (crucially) are statistically far more likely to have voted Leave (reference D).

The overall effect is that over time there is a net inflow of Remain voters to the voting population, while there is simultaneously a net outflow of Leave voters. With this backdrop, the question is this — at what point will the balance tip? Assuming that nobody changes the way that they voted in 2016, when will the composition of the voting population have changed sufficiently that there will statistically be more Remain voters than Leave voters?

The answer: July 2020.

Using publicly available statistics and making some simplifying assumptions, a demographic model implies that this is when the scales topple. Just 9 months after the “official” leaving date of 31 October 2019, the model suggests that the decision to withdraw from the EU will be an undemocratic one.

July 2020 — as an answer — clearly depends on the composition of the model. Naturally, this invites scepticism. Therefore, the model is available here, with all assumptions and source statistics clearly outlined and further explanations offered as to how the model works.

This model — like all models — is not perfect. The assumptions are restrictive and relaxing them may give a different result. For example, modelling voter turnout would push the estimated date further away. Equally, modelling the change in voters’ views could push the date further away. There are many ways to adjust the model to change the estimated date at which the balance shifts — but the key point remains. In the foreseeable future the voting population will not have voted to leave the EU.

The 2016 referendum has an expiry date imposed on it by its demographic composition, and the only resolution is to renew the mandate via a second referendum.