There is widespread consensus (according to online surveys and opinion polls) that the best art material shop in London is the Cass Art, located in Charing Cross, just next to the National Gallery.

Basically, what makes it the most preferred art material shop is its having everything you need for your creative needs in a small space: A wide range of sketchbooks, paint, brushes, and, more importantly, its being staffed by real artists, who know exactly what you need.

Finally, Cass Art is loved for its affordable procces, as its manifesto says, which indicates a strong commitment to what art really is what art means for artists. So, don't expect to find the typical impersonal chain store that offers everything but without the slightest human touch for the profession.