And of course the margin of victory in 2016 was far smaller than the number of fresh voters who have joined the electoral roll since then, most of whom are generally accepted even by Brexiteers to be remainers.

There again, it is also generally accepted that it was (generally) the older generation which voted Brexit. A large number of voters will also have moved into this group (partly made up for by those who have died).

The whole electorate have grown older, so it is not necessarily just the youngest group which has increased in numbers.