I recently purchased a Trek road bike from the Trek store in Battersea.
Edwin, Carlos and the team there were friendly and very helpful, with sound advice on the bike, its features and technical matters. I was also able to go for a test ride safely nearby - a helmet and flat pedals were provided.
Technical and mechanical support is available after purchase and they have a good range of accessories, kit, plus an excellent service department in store.
Buying from Trek Battersea was a great experience, as well as the bike being competitively priced.