LONDON LANDING SITES
There are 3 parts to this:
1. London, under the Heli Routes, is a congested area and you will need CAA permission against Rule 5(2)(c) (the 1000 ft rule) to land unless you are using a licenced or government airfield.
2. You are not allowed to land off the heli routes, except at a licenced or government airfield, without CAA permission (Rule 5(3)(c)(ii).
3. If your site is in the Specified Area then you need CAA permission against the Air Navigation (Restriction of Flying) (Specified Area) Regulations 2005.
It looks as though you may need permission on all 3 counts.
Fortunately all are dealt with by the General Aviation Dept in the Belgrano.