There is a little used method offered by Royal Mail for getting a proof of delivery. This is called ADVISE OF DELIVERY. The current cost of this service is just 40p. Most Post Offices have forgotten this service even still exsists. What you do is file in a card with both Addressee and Sender details, Office of posting and date. Place the card in the plastic self adhesive packet provided and stick it to the front of your letter / packet along with a RED label with the letters AD on it. When the item is delivered the delivery Post-person will get the Addressee to sign the card then it is returned to the sender. Note this is not a tracked service or insured service, but it will give just that bit more piece of mind than just a plain mailing.