Actually, it's not just that, under UK law a disclaimer cannot cover you in the case of death or serious injury (apparently) ... unless it can be proved that the person that signed knew and understood the risks ... almost impossible to prove.
(That is if I understand it right, feel free to correct me)
GR14-- nothing is demanded of the cadets. In fact, most of them volunteer, when our cadets do the Southend Airshow the sign up list is usually filled very quickly, and everyone looks forward to the chance to get to see aircraft up close.
-D