this was the item I found on consumer direct website
"If a price has been agreed between the salesperson and myself, can they change their minds?
If a price has been agreed between the sales person/manager and myself on a specific item (electrical goods), does he have the right to refuse to hand over the goods, which have already been paid for, if he then realises a mistake has been made on the price?"
"If you'd already paid for the item then you had a contract with the shop to buy the item at that price.
As the contract had already been made, it was too late for the shop to alter the terms of the contract and you're entitled to the goods you've bought.
It would've been different if you hadn't paid for the goods when the shop discovered the error in the price. No firm contract would have been made yet to buy them at the price advertised and the shop would have been free to change the price."
Obviously this does not refer to internet but could mean something.
Sorry its taken a couple of days for me to post but am off on hols tomorrow so hectic weekend.