I cant see the pics at work but i posted up a "Cars of London" thread a couple of weeks back.. Locations i saw these sorts of cars at were
Park Lane (Dorchester Hotel)
Hyde Park Corner (Lanesborough Hotel)
Wilton Place (The Berkeley Hotel)
Then Knightsbridge, around the Harrods Building there are loads
Also you might want to try down Marylebone Highstreet as it goes towards Selfridges and there are lots of nice cars round that way.
Kings Road in Chelsea if you want to see LOTS of Bentley / RR's
Hope this helps and sorry for a thread hijack.. Fellow Brit here :clap:
