Location, location, location ! You know quite a few things about Gary's current house and TTC has now located one of his former homes in London. Howard pointed at his former flat on the Beautiful World DVD saying something like "this is where Gary used to live" and I can understand why he does not live there anymore. The flat is on one of the upper floors offering nice views across the city and the Thames at night. IMHO the view during the day is a bit grey - many not so beautiful buildings opposite the flat and dirty water when looking down the terrace.
The building he used to live in is called "Waterside Point"; a development of luxury flats with concierge and secure parking in Southwest London. TTC is still working on the exact value of Gary's former apartment - depending on size, view and interior some flats are available at below £500,000, while others are £2,000 000 or more.
Feel free to get in touch with TTC for directions :-)