Hi,
When I first went to London many years ago, there were a half dozen Toy/Model soldier outlets. Sadly they are now few and far between. However the best central one is the Guards Toy soldier shop (MKL) ,it is situated on Birdcage walk near the Guards Museum/Wellington barracks (quite close to Buckingham palace)they stock the full Britains range (and much more)the shop is large with many well laid out glass cases. Also.........the Armoury at St James in an upmarket arcade (mall!) in Mayfair. They stock a lot of Frontline figures, plus many others. The shop also deal in military antiques. You could also try Hamley's of Regent street which is one of the capital's premier toyshops. Last time I was there, they had a reasonable display of K&K and Britain's.They are the main places I can think of in central London. Hope that is useful for you. Cheer's! Johnboy