You can flip a car at North Weald, but it does depend on the kind of car. Jo had her old Aygo on three wheels and it was very leany when we did our last day there, and then a couple of weeks later a Fiat Panda went straight over as it took the high speed bend. To be fair to Walshy he put everything right out of his own pocket and took full responsibility for the incident, and I believe he's re-adjusted his views on what cars he will and won't allow you to do a day there in light of this.
That said, you're never going to be able to roll a sports car of any kind there unless you're being particularly stupid, and I mean ignoring Walshy completely and going past the drain and digging your wheels into the grass. Honestly, that is never going to happen in a million years though.