There's nothing quite like B&H in the UK, in my experience i would not recomend Jessop's, ok so some of their staff know what they are talking about but most are muppets, who will try and sell you products with the highest profit margins so they get their bonus's, which i suppose is fair enough beacuase they're being underpaid anyway. I would recomend Harrisons in Sheffield, Morris's in Oxford, there's loads in London, calumet are good - the have everything in stock. Fixation really good, especialy for repairs.
If buying something expensive i would advise going to NY and going to B&H, the money you save on equipment can pay for flights/hotel etc.