Best Designer's Bookstores In London?

I will be in London for a couple of days this spring. During these days I would like to take the opportunity to rummage some designer’s bookstores. My special intersts are marketing, design-management and design-research. Does anyone have suggestions where I definately should go to?

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Also check out the big museums :

Tate modern has a massisve bookstore and the design museum has a good one too.
Also check the Serpintine gallery in hyde park, it has a nice small one.

But to be honest, amazon beats the lot hands down