A number of options are available:

• Has your shipment arrived in the United Kingdom, cleared through customs and the recipient has received the parcel in the United Kingdom? In that case, your customer will have to take care of a new shipment with a new label, customs documentation and associated costs. 
• Did you provide a return address in the United Kingdom? The recipient may then return the parcel to that address.
• Your shipment has arrived in the United Kingdom, already cleared through customs but not send to the recipient. The parcel can still be returned if VAT has been paid.