Good Lawyer Guide's response

The retailer must sell goods which are of satisfactory quality. The fact that the sofa was in the sale does not affect this statutory right. However, if the damage was pointed out to you at the time of purchase, or if the damage was clearly visible to you, you would not be able to return it. If good are sold as ‘damaged’, they should be clearly marked as damaged, in which case they would be non-returnable.
But if you did not know the sofa was damaged, you do have the right to insist on a refund or replacement. It is worth remembering that simply changing your mind and deciding that you don’t like an item does not give you the right to return it.