Another thing to consider is there are a number of 'chain' stores on the street where it isn't obvious...
ASK, Kamla, Harp + Macdonalds (on oxford street) are own by three brothers who actually share stock, if one is low on a particular item so they generally offer consistent pricing unless one of the managers can do a deal.
C&A also have a couple of stores too.
If you do your research beforehand you can get a deal but these guys haggle everyday so they will always try to pursuade you to pay more. Remember that it's YOUR money!
Have fun and good luck!
p.s. I normally buy from Micro Anvika or the ASK chain of stores. They aren't dodgy like some of the other stores and the customer support can be really good. I had a very positive experience getting my Shure E500 PTH's replaced on the spot without receipt or packaging from Micro Anvika.