I suppose it's just possible that they could check that everyone on the pitch has an entry ticket on arrival, but bearing in mind that there's bound to be some to-ing and fro-ing, I just don't see how that could work. I'm trying to remember as I've walked in and out of the enclosure (many many times) whether there is a way to just walk from the campsite in and my mind is telling me that I'm sure there is...but I just can't fathom how that would work. There's bound to be someone along soon who will know for sure....