The term "unitary authority" was first used in the Redcliffe-Maud Report in 1969 in its current sense of a local government authority which combines the functions of a county council and a district council. Strictly speaking, the term does not necessarily mean a single level of local government within an area, because in some cases there are also parish councils in the same area.
Although the term was not applied to them, county boroughs between 1889 and 1974 were effectively unitary authorities, that is, single-tier administrative units. Before 1889, local government authorities had different powers and functions, but from medieval times some cities and towns had a high degree of autonomy as counties corporate. Some smaller settlements also enjoyed some degree of autonomy from regular administration as boroughs or liberties.
The Local Government Act 1972 created areas for local government where large towns and their rural hinterlands were administered together. 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. The resulting structural changes were implemented between 1995 and 1998. Bristol, Herefordshire, the Isle of Wight and Rutland were established as counties of a single district; the district councils of Berkshire became unitary; the counties of Avon, Humberside and Cleveland were broken up to create several unitary authorities; and a number of districts were split off from their associated counties. The changes caused the ceremonial counties to be defined separately, as they had been before 1974. The review caused 46 unitary authorities to be created.
A further review was initiated in 2007 and was enacted in 2009. The review established Cornwall and Northumberland as counties of a single district; established unitary authorities in County Durham, Shropshire and Wiltshire covering the part of the county that was not already split off in the 1990s review; and divided the remainder of Bedfordshire and Cheshire into two unitary authorities. The review caused nine unitary authorities to be created.
In 2017, it was proposed that two unitary authorities be formed to cover the ceremonial county of Dorset. One of the authorities would consist of the existing unitary authorities of Bournemouth, Poole and the non-metropolitan district of Christchurch, the other would be composed of the remainder of the county.  In November 2017, Secretary of State for Communities and Local Government, Sajid Javid stated that he was "minded to approve the proposals" and a final decision to implement the two unitary authority model was confirmed in February 2018. Draft statutory instruments for the creation of two unitary authorities to be named Bournemouth, Poole and Christchurch and Dorset have been laid before parliament.  Joint committees for both authorities have also been formed.  
Two competing plans were drawn up for Buckinghamshire. One plan would see the abolition of the four district councils resulting in the existing county council becoming a unitary authority. The other plan would see the formation of two unitary authorities, one authority would be formed through the merger of the three existing districts of Chiltern, South Bucks Wycombe with the other formed by the existing Aylesbury Vale district becoming a unitary authority.   In March 2016, Communities Secretary Sajid Javid indicated that the single unitary authority option would be pursued over the two unitary authority model. 
In late 2017, plans were drawn up for local government reorganisation in Northamptonshire which would see the existing eight councils in the county consolidated into a single unitary authority with a view to saving £29 million per year.  In March 2018, an independent report commissioned by the Communities Secretary suggested that a two unitary authority model should be pursued instead of a single unitary authority model. This would see the existing county council and district councils abolished and two new unitary authorities created covering the north and the south of the county.  The southern authority would consist of the existing districts of Daventry, Northampton and South Northamptonshire and the northern authority would consist of Corby, East Northamptonshire, Kettering and Wellingborough districts. 
In 2016, Oxfordshire County Council put forward a 'One Oxfordshire' proposal which would see Oxford City Council and the four other district councils in Oxfordshire abolished and replaced with a single unitary county council for Oxfordshire. In 2017, Oxford City Council voiced their opposition to the proposal. A decision on whether the proposal will go ahead was to have been announced in March 2017.