If a second referendum were to be held in late March 2019, it's plausible that a
Remain vote would win even if nobody changed their minds.
The process below involve some large assumptions and some numbers are educated guesses, but it does paint a reasonable picture of the effect of shifting demographics.
In June 2016, the results were:
Leave: 17,410,742
Remain: 16,141,241
These numbers would naturally change for two reasons:
- People no longer being eligible to vote (now deceased).
- People newly being eligible to vote (now 18+).
1.
Roughly 600,000 people die each year, or 1,650,000 between the referendum and UK's leaving date (March 2019).
Life expectancy is 81.6. Reasonable estimates at this age range could put turnout at 85% and the
Leave vote at 70%. So making that adjustment, using voter eligibility of 95%:
Leave: 17,410,742 - (1,650,000 * 0.95 * 0.85 * 0.70) = 16,478,080
Remain: 16,141,241 - (1,650,000 * 0.95 * 0.85 * 0.30) = 15,741,529
2.
Roughly 2,100,000 at the last referendum were younger than 18 but older than 15.25 (18 minus 2.75 years since the referendum)
Reasonable estimates put the turnout of 18-24 year olds to 64%, and the
Leave vote at 25%. So making that further adjustment, using voter eligibility of 90%:
Leave: 16,428,992 + (1,650,000 * 0.90 * 0.64 * 0.25) = 16,780,480
Remain: 16,141,241 - (1,650,000 * 0.90 * 0.64 * 0.75) = 16,648,729
The exact %s are certainly open to debate, but the numbers here close the Leave-Remain gap from 1,269,501 down to 131,751, for a 90% reduction.
If there was a slight shift in the number of new voters turning out and their
Leave vote %, it could flip the referendum result.
And that's only at March 2019, based on nobody changing their minds.
Imagine a longer-term view, or allowing voters aged 16+ (e.g. Scottish independence vote).