In 1974 a two-tier administrative structure of (shire) counties and non-metropolitan districts was set up across England and Wales, except for the Isles of Scilly, Greater London and the 6 metropolitan counties.
Council functions were divided according to the level at which they could be practised most efficiently.
In consequence, counties took on functions including education, transport, strategic planning, fire services, consumer protection, refuse disposal, smallholdings, social services and libraries, whereas the local authority districts (LAD) had responsibility for local planning, housing, local highways, building, environmental health, refuse collection and cemeteries.
Responsibility for recreation and cultural matters was divided between the two tiers.
Following the Local Government Reorganisation in the 1990s, major changes were implemented to create administrations most appropriate to the needs of the area concerned.
The key feature of this change was the introduction of unitary authorities: single-tier administrations with responsibility for all areas of local government.
Between 1995 and 1998 these were established in a number of areas across the country, especially in medium-sized urban areas, whilst other areas retained a two-tier structure.
Further local government reorganisation occurred in 2009 and there are currently 56 unitary authorities in England, and 27 shire counties split into 201 (non-metropolitan) districts.
Note that due to the changes in Cornwall, the Isles of Scilly are considered a unitary authority for coding purposes.
Counties, LADs and unitary authorities are subdivided into electoral wards/divisions.
On 1 January 2011, the GSS Coding and Naming Policy was implemented. This policy led to the creation of a new coding system (the 9 character codes) for all geographies held by ONS. For further information, please refer to the Code History Database (CHD).