it is so a marshall cannot stick a finger through onto a moving spur etc.
as for davids "F" question, yes you drop by 1 grade per year so if you are an f3 and do nothing the next year you drop to f4, and so on.
for example neil cragg drops to f2 this year (and would be my bet for the BRC
). darren bloomfield who has been missing for a couple of years will be f3, the richards Cree/barton/taylor will be anywhere from f3-f5, so if they all come back this season the top f3 trophy at a national will be a tough one to win!!.
it is of course entirely feasable for the podium places at all the nationals not to contain an F1. wonder what the odds are at corals?