1. No. A margin of victory in a popular vote is still a margin of victory. Anywhere else you draw the line is perforce arbitrary and unfair. Equally, such a rule would always favour the status quo. After all, had the vote percentages been reversed, do we think we'd have left the EU? Of course not. We'd have stayed in, meaning that, whichever way the vote went, the Leave voters were effectively disenfranchised.
2. This is a bit retarded. You realise we have a system of secret ballots, yes? And that there is therefore no way of knowing who did or didn't vote to leave?