Billy the Fish
Technocrat
Well they couldn't have gathered data on how different demographic groups voted before June 23. They would have got the information either on exit or later.
The BBC didn't bother doing an exit poll for the referendum because it wouldn't be accurate. The general election exit polls are based on previous elections so they know their sample is representative of the population. On that basis I'd be instantly skeptical of any other polls, unless they'd taken a huge sample.