Like Subculture I live in North London and use 308 Hobbies and Hobby Stores in Camden Town. Both are what would be termed traditional model shops, although these days that tends to mean floor to ceiling stacks of large lavishly illustrated boxes of ARTF planes, and not a great deal of model boat related stock.
I find the 4D Modelshop, based underneath the railway arches in Leman St. E1, a much better bet. Although primarily catering for professional architectural modelmakers it has a vast range of model making materials (ABS, wood, metal, etc.), tools, glues, fillers, and accessories, of much interest to we model boaters. It bills itself as a 'creative materials resource centre' which I think is a poncey name for a model shop, but it does have a huge range of stuff, knowledgeable helpful staff, and is near to St. Katherine's Dock. Check it out if you get the chance.
Mike