I think what needs to happen is someone contact them and ask what the time frame is for them to check 'eligability'
that way if the order goes through WITH discount then after 28 days without question the items are yours at that price.
It says that '', after accepting your order, we find that you were not entitled to use the code or did not meet all the terms and conditions of its use, we may reverse the benefit that you obtained. If you transacted on a cash basis e.g. by debit or credit card, we may take a further payment, equivalent to the value of the benefit obtained, from the card used. If you transacted on a credit basis, the value of the benefit obtained may be charged to your credit account.''
But how long do they legally ahve to do this?
They couldn't decide after 4 years that suddenly they can charge you full price.
So what is the cut off point.
Surely it should be something like 28 days, so if after 28 days you have no had notice of being charged the full price then the item are free to be opened without the possibility of full payment being owed??