Most Jacobs stores will have a decent range of gear. Prices aren't the cheapest, but I've found the service is always good.
No experience of LCE, but they usually get good recommendations.
Jessops can be expensive, though sometimes have offers. They usually just employ sales people now, rather than people who know cameras.
Plenty of places on Tottenham Court Road do cameras/electronics stuff, however they sometimes have grey import stuff and the really I don't trust those types of shops.