In the United Kingdom many "local carriage labels" have been issued by offshore islands, which in some cases had a genuine use to pay for transport of the mail to the mainland by ferry. Others were produced simply to sell to collectors and tourists. Usually they had to be placed on the back of the envelope, with a conventional stamp on the front to pay for onward delivery by the official postal service. Islands for which such labels have been issued include the Summer Isles, Lundy and the Calf of Man.