These are the terms and conditions when ordering online. I'd imagine the same terms apply when purchasing from a shop.
Quote:
You may also cancel your order up to fourteen (14) days after delivery of the order to you. You may do so by contacting Us or, alternatively, by returning the products to any Gamestation store, in accordance with the provisions below.
Unless items are damaged or faulty when delivered, you may only cancel your order if:
1. in the case of new software and/or hardware the items are as new, in a saleable condition, unused (except to the extent reasonably necessary to examine them), undamaged and, in the case of any game or other computer software, provided that it is still in the original sealed packaging; and
2. in the case of pre-owned software and/or hardware the items are in the same condition they were in when we delivered them to you, have not been used by you (except to the extent reasonably necessary to examine them), are undamaged and, in the case of any game or other computer software, provided that it is still in the original sealed packaging (if applicable).