Prices in UK are high -- typically double to triple the US (NYC) price ... which is why Brits fly to JFK to do their shopping. Even for goods made in England it is generally cheaper to buy in the US. As for the LHR stores, one good thing about them is that there is ample selection and prices and quality are identical to high street, so you won't do better by shopping in London unless you know a specific store or item. The Burberry store at LHR is identical to what you will find in London, and may well be cheaper (however, I am sure it is cheaper in New York for genuine Burberry).