Chopjock;
Exemption from 5.3.C is mandatory for a flight into that area, and possibly 5.3.D for a single. Oh sorry, you won't get a single in there because its a confined area (defined by the CAA as surrounded by habitation, industry etc, not a postage stamp size piece of grass)
Noorpilot;
Why don't you go and talk to an AOC operator who can self authorise such a flight and do it legally in a twin. I've landed at Syon many times, it is a beautiful place for a wedding, and a wedding is no place for any form of illegal helicopter flying, which is what your first post suggested.
And the LHR traffic is below 1500' there
SND