Contrary to above answers, I think you CAN find the delivery address of any PO box, by asking Royal Mail. Whilst you may need to provide your own details in the first place, if your reasons for the enquiry are genuine (ie.a business owes you gods or money), what do you have to hide. The Royalmail website states that if you need anonymity for your PO Box (examples given are of a Womens Refuge or if you are in the Security Services) that you need a letter of endorsement from your local Police Station.