Thanks for the feedback. To answer your question on the 500' rule:
CAP 393 says (I've deleted the bits that don't apply):
1(e) An aircraft shall not fly closer than 500 feet to any person, vessel, vehicle or structure.
(c) Paragraphs (1)(d)(i) and (1)(e) shall not apply to the flight of an aircraft over or within 1000 metres of an assembly of persons gathered for the purposes ofwitnessing or participating in an event which consists:
(i) wholly or partly of an aircraft race or contest if the aircraft is taking part in such race or contest or is engaged on a flight arranged by, or made with the consent in writing of, the organisers of the event;
(iii) wholly or principally of a flying display for which a permission under article 61 of the Order is not required, if the aircraft is taking part in such display or is engaged on a flight arranged by or made with the consent of the organisers of the event.
The way I read 2(c)(iii), it means that so long as I have the organisers' permission, I don't legally have to comply with the 500' rule. It doesn't seem to matter whether it is a 'display' or not in legal terms.
I stress again that I would not break the 500' rule if it wasn't safe in the circumstances - I'm just finding the legal aspect difficult to decipher (which I guess is why they're trying to simplify it at present...)