It is alleged that a very substantial part of the Leave campaign funding came from overseas (which is strictly against the law) possibly from Russia.
A large proportion of this money was paid to Cambridge Analytica who illegally harvested peoples data on facebook, to target them with micro adverts, not all of them we know what they said.
Up to £8 million is under investigation.
Add this to the blatant lies of the Vote Leave campaign which they now admit were untrue (the 350 million a week for the NHS for example) is there any legitimacy left in the result of the referendum?
This is what the polls indicate
uk.businessinsider.com/brexit-polls-show-britain-wants-to-remain-in-eu-2018-9