The Vanguard site is in the Isle of Dogs. I worked a Star Speed from Blackbushe in to there today. However, the traffic always goes to and from a Private Site in Kent - so I am not aware of it being used by anyone else other than the same guy. There is also a fairly regular drop off in St Pauls area. (Near the Honourable Artillery Company's barracks)
Other HLS traffic I worked in the zones today went to Battersea Heliport, Battersea Power Station and some military traffic into Army barracks.
Oh yes, there's always quite a bit in to Buck Pal/Ken's Place if you can get approval!!
I take it you are worried about the Specified Area. As you know only aircraft on Heli routes or with the Authority of the CAA are allowed in there if Single Engined. The only way I can think of around it is if you are close to the edge of the Area as you only need to be able to alight clear of it!!
Good luck