For comparison's sake, Amazon is selling the 20GB iPod for $399. Using your estimate, that means that Amazon.co.uk should be selling it for £235. It's actually being sold for £289.

There always seems to be an added fee for buying US-oriented electronics in the UK. Maybe the iPod isn't the best comparison, since Apple keeps its retailers under its thumb, but still, it's the best comparison I can come up with.