As far back as I can remember, ALL people who entered a UK race track, either, signed on the dotted line, as officials or drivers OR, had an entry ticket with a warning on the back, reinforced by strategically placed signs, saying "Motorsport is Dangerous" and therefore by being there, you accepted the risks in whatever capacity.

Although it might not satisfy OSH or the courts, in the pre-litigation times, it seemed to work well enough. Maybe we need to step back a wee bit to those times, but I can't see it happening.