Pace...
Don't give a tuppeny fart about the rights or wrongs or enquiries or legalities... just pointing out that an altitude of 400 feet is impossible for the average model pilot to assess. Who cares about "the subsequent court of enquiry"...the point is that you cannot rely on models staying below 400 feet, so you could easily end up "dead right". Far better to avoid them by staying well above this yourself, surely?
Flying is full of things you can't measure or assess by eye with any accuracy. RAF aeroplanes fly low level at 250 feet, and we were told this was about twice the height of a pylon and you could see the legs on cows but not on sheep... And just how do you assess the VMC 1500 metres horizontally clear of cloud thing? Better to stay well clear....