The Pyper family's control of the constableship concluded in 1754, and George II then appointed a sequence of constables who became responsible for running the castle and county gaol on behalf of the duchy of Cornwall. In 1764, the north gatehouse was partially demolished by Coryndon Carpenter, a former mayor of Launceston and the castle's constable, who used the materials to help built a new mansion alongside the castle, called Eagle House. Parts of the north-west curtain wall were destroyed in the process of his landscaping work. When the artist William Gilpin visited in 1775, he praised the picturesque condition of the ruins.