yep, i'm aware of the being-stood-up issue!
i'm in central London - Camden/Chalk Farm area.
i emailed FBAS to see if they know of any Society's in the area, they didn't have any listed though.
looking on PFK, it seems everywhere but north/central is covered, there's a South London Aquarist Society, Essex is pretty well covered, the one by Heathrow is the Hounslow and District Aquarists' Society, as well as the south coast being well covered also.
oh, there's a West London Reef Club - not much good as I only do freshwater though.
So I think it's this sliver of central london and north london (barnet, islington, maybe enfield) and as far as east goes, the other side of the M25 is pretty well covered by essex clubs and societys, the inner side of the m25 such as hackney, bethnal green and tottenham less so.
at least thats as much as I can find on the web.