i think there may be a rule about them withdrawing the item for a set amount of time and re-advertising it with the correct price, but this may only apply to shops in the highstreet.. saw it on tv once with a clothes shop.
they can and will refuse to sell it to you, but if you can pay online you could attempt to buy it they might not even notice! and send it out fro the money you paid, it'll probably be automaticly sent without anyone checking anything..
if they do notice, then they will have to refund your money, so basicly you cant lose from trying!