Shops
 

Been a while since I have been to a bike shop in London. Motorcycle City were crap but they had a big selection of gear to look at and then find better prices elsewhere.
Where is good now?

Depends where in London you are/are going and what you are after.

Sondel Sport at the top of Islington is friendly but mostly high-end stuff. http://www.sondel.co.uk/

J&S in Greenwich is quite an aladdins cave.
http://www.jsaccessories.com/

Rivetts in Leytonstone is okay. Not very big though.
http://www.rivetts.co.uk/

Harpers in Romford okay as well. Also pretty small.
http://www.harpersraceshop.co.uk/cat14_1.htm

Of the four, only J&S is worth going out of my way for (unless I want something Dainese, which is about every 3 years).