The islands have had a unitary authority council since 1890 , and are separate from the Cornwall unitary authority , but some services are combined with Cornwall and the islands are still part of the ceremonial county of Cornwall . This council is part of the UK and currently known as the Council of the Isles of Scilly . The Council of the Isles of Scilly is a separate unitary authority to the Cornwall Council unitary authority , and as such the islands are not part of the administrative county of Cornwall .