Exit polls are generally done in normal British elections. No formal exit poll is being done in this case, because there’s no data that can be used to model the numbers based on previous elections, because there hasn’t been a previous election like this one.
Normally, you have data, so you know how particular booths lean, which ones report early, etc so even a very limited exit poll can be extrapolated quite accurately - this isn’t the case here.
I think Britain leaves tonight. Cameron is out of Downing Street by Sunday morning. New Prime Minister= Stephen Crabb.