Another option is to look on the other EU Amazon sites from the UK. The Euro is weak against the pound so you can save that way and don't have to pay any import taxes (benefit from EU membership in the UK while it lasts!). I often find things much cheaper on Amazon.de, Amazon.fr and Amazon.it (but you need to be willing to wait between 3-7 days for delivery usually).
Good call! I got a HD600 from amazon.fr for £190 about 6 months ago; some good prices to be found from time to time.
And amazon.it currently has the RS1i for 600 euro (£487) which is not too bad. I'd expect to pay a bit extra for delivery (think it was 10 euro for the HD600s) but that's still under £500.