Freya C.
Yelp
One of the cheapest art stores in London, and this is the flagship-mother-of-them-all.
Really friendly and helpful staff- if you can't find something you need in the store they're guaranteed to have a good suggestion of where else you might obtain it.
Excellent student discounts (15%!) just ask in store, and check out the paper cards they shove in your bag with any purchase, often great deals are to be discovered (just got a 2 for 1 Whitechapel Gallery offer) so look before throwing away!
Top floor has 101 types of paper pads and sketch books as well as specialist papers. Middle floor (on to which one enters the store) is a mixture of paints, pens, brushes and various other artsits tools. In the basement is kiddy-fun stuff, stencils, architectural modelling materials, rulers, cutting knives, decoupage, patterned papers, ink pads and stamps. And much much more of course.
If, like myself you could easily lose half a day trawling through the wonders of an art store leave ample time for your exploring, there will be many wonderful discoveries!