 The concept of unitary units was abandoned with a two-tier arrangement of county and district councils in all areas of England, except the Isles of Scilly where the small size and distance from the mainland made it impractical.In 1986 a broadly unitary system of local government was introduced in the six metropolitan counties and Greater London, where the upper-tier authorities were abolished and their functions were split between central government, the borough councils and joint boards.A review in the 1990s was initiated to select non-metropolitan areas where new unitary authorities could be created.