The biggest move has been from the 2016 non voters to Remain
The above chart, by professor John Curtice, is in the latest edition of Prospect magazine and is designed to show how opinion on Brexit has moved on since the referendum period
As can be seen by a whisker more Leave voters than Remain ones have now switched.
The biggest move has been amongst those who didn’t vote in 2016. A significant proportion of this group will be those who were too young to have taken part in the referendum. The balance will be those who for whatever reason didn’t take part.
This, of course, doesn’t really matter because Mrs May has said that there will not be another referendum and when she makes statements like that about elections we all know how much we can rely on them.