HP-shopping in London

[sophiamcl]

Hello all!
I'm a lurker surfacing for some advice. In a few weeks time I'll be in London 
for a couple of days. Since Sweden (where I normally reside...) isn't the best 
venue for finding HP-stuff, I thought I'd take the opportunity to look for some 
HP-paraphernalia while in England. Trouble is, I haven't a clue where I might 
find the good stuff--or any stuff. Are there any Londoners on this list that 
would care to advise me on where to go? 

Sophia