I bought mine from Amazon, I paid £804 for the £899 model (2.26 GHz). Before the VAT increase. Amazon price seems to increase slowly as stock disappears. Then it goes out of stock, and you get redirected to an outrageously priced partner. Then after a week or so Amazon gets some more stock in and starts again at a low price.
Looking today it's on at £835 (2.26 model)
Not sure about the 14 day return period, that might be only in the US. Of course you have your 7 day cooling off period in the UK, but that probably won't apply if you've used the Mac