All Apple gear is shipped here direct from the Far East - as it is to the US!
But I bet the leases on Covent Garden, Regent Street and the other Apple Stores (which are all, generally, in upmarket malls or shopping areas in the UK) aren't cheap, not to mention the staff for whom they have to be paid a British living wage, employer's national insurance contributions, pension fund etc.
I can't present any numbers, but this would account for some of the difference on top of currency fluctuation.