Unitary authorityUnitary authority is a term used in the United Kingdom for a local government body which forms a single tier of administration. Traditionally there would be a two-tier arrangement where each county had a council and contained multiple districts with councils of their own. The area administered by a unitary authority is called a "unitary authority area" or sometimes a "unitary district".
Unitary authorities can be created by statutory instruments, so do not require separate legislation, under the terms of the Local Government Act 1992. Typically a district of an administrative county is designated as a new administrative county, but without a county council. The borders of the original administrative county are adjusted to exclude the unitary authority area. In common usage unitary authority areas are not usually refered to as counties, although there are exceptions such as the unitary authority of Herefordshire, which along with Rutland was a reinstatement of an administrative county lost in the 1974 reorganisation, and the road signs of Herefordshire now refer to it as a county.
In some cases, such as the boroughs of the metropolitan counties and Berkshire the unitary authorities are not legally counties in their own right, but have instead had all functions transferred to them and the county council has been abolished. This is in practical terms the same thing.
Scotland and Wales consistently use unitary authorities. They have been becoming common in England since the 1990s. However the two-tier arrangement (increasing to three-tiers, for the remaining county administrations) has remained in a different form due to the introduction of a regional level of administration.