That isn’t the correct question.
The correct question is, how many would equivocate or reluctantly accept it, such is their visceral hatred of the EU? I would guess around 20%. There would be others who would be strongly opposed but would still, in the final analysis, prefer we were aligned with the US, rather than Europe. Some of that will be informed by their politics, or be cultural, but others simply because they would feel safer being aligned with the biggest bully in the playground.
I think combined they would at least amount to 35% of the UK population, possibly more.
That’s more than enough to represent a huge schism, given the existential nature of the choices available.