Heading to London - Hifi Store/Record Shop Recommendations?

Greetings all,

Just found out I will be in London for 5 days at the end of the month. I'll be fairly free on the first day and would like to listen to some gear I might not normally see here in Atlanta. I would also like to  pick up some new vinyl if possible. 

Any recommendations for good hifi shops or record stores near the Marllebone neighborhood? I believe that's near the Oxford Circus station and The British Museum.

Thanks for the suggestions!