Before 1782 state business relating to the UK's internal affairs was shared by the two Principal Secretaries of State. In 1782 they were given charge of home and foreign affairs respectively.
The Home Office was formed from the staff of the former Southern Department.
The functions of the Home Secretary derive from two main sources: royal prerogative and parliamentary legislation. He is the residuary of all functions relating to the UK's internal affairs not assigned to other departments of state. Main functions in 1782 were: answering petitions and addresses to Sovereign; advising Sovereign on royal grants, warrants and commissions and exercise of royal prerogative; issuing instructions on behalf of Sovereign to officers of the Crown, Lords Lieutenant and magistrates, mainly concerning law and order; and operation of Secret Service within UK. He is also responsible for protecting the public and safeguarding the rights and liberties of the individual.
After 1782 more specific functions were added, of which the following are still exercised by the Home Office: regulation of aliens (from 1793); naturalisation (1844); penal system (1823); police service (1829); control of explosives (1875), firearms (1920), dangerous drugs (from the First World War) and poisons (1933); electoral administration (taken over from Ministry of Health in 1921); civil defence (1935); and fire services (1938).
Some minor functions were transferred from other departments: appointment and supervision of Railway and Canal Commissioners from Board of Trade in 1919; confirmation of certain byelaws in 1947, and regulation of markets and fairs in 1948, from Ministry of Health; grants for school crossing patrols from Ministry of Education in 1953; and regulation of escape-ways in certain buildings from Ministry of Housing and Local Government in 1964.
The Home Secretary is responsible for the confirmation of local authority byelaws concerning good rule and government, parks and pleasure grounds, and street trading. Other local authority byelaws (public health, nuisance, buildings) are the responsibility of the successors to the Ministry of Health.
Since 1782, some responsibilities have been transferred from the Home Secretary to other departments:
- 1794: control of military forces, except for maintenance of public order and home defence, to Secretary of State for War.
- 1801: colonial business to Secretary of State for War and the Colonies.
- 1804: responsibility for Barbary State consuls to Secretary of State for War and the Colonies.
- 1855: yeomanry and militia business to War Office.
- 1871: oversight of work of General Register Office (since 1837) to Local Government Board.
- 1871: Local Government Act Office became part of department of Local Government Board; in 1872 Board took over duties of Home Office in relation to highways and turnpikes.
- 1875: Treasury assumed responsibility for new central Registry of Friendly Societies which replaced three separate registrars for England and Wales, Scotland and Ireland respectively (responsible since 1845 to Home Secretary
- 1885: responsibility for Scottish affairs to newly-created Secretary for Scotland.
- 1886: Fisheries Inspectorate to Board of Trade.
- 1889: supervision of Land Commissioners to Board of Agriculture.
- 1900: duties under Burial Acts and control of Burial Grounds Inspectorate to Local Government Board.
- 1905: duties under Housing Acts to Local Government Board.
- 1919: administration of Aerial Navigation Acts to Air Ministry.
- 1919-1921: functions in England and Wales relating to Anatomy Inspectorate, infant and child care (restored to Home Office in 1947), lunacy and mental health, and health sections of Factory and Workshops Act 1901 to Ministry of Health.
- 1920: Home Office's responsibility for official representation of Britain abroad in labour matters to Ministry of Labour.
- 1920: Mines Department and Inspectorate absorbed in the new Mines Department.
- 1922: Home Secretary retained ultimate responsibility for affairs of Ireland until 1922 and for Northern Ireland until 1972, relations with Irish Free State being assigned to Colonial Office.
- 1923: administration of Order of the British Empire to Treasury.
- 1925: Ministry of Labour took over duties concerning registration of trade unions under Trade Union Act 1871.
- 1931: Ministry of Health took over supervision of clerks of county councils.
- 1934: Ministry of Health took over supervision of proceedings of metropolitan boroughs.
- 1937: preparation of road accident returns to Ministry of Transport.
- 1938: administration of Imperial Service Order and medal to Treasury.
- 1940: Factory Department and Inspectorate to Ministry of Labour.
- 1945: supervision of workmen's compensation scheme to Ministry of National Insurance.
- 1947: regulation of advertisements to Ministry of Town and Country Planning.
- 1947: supervision of interment fees to Ministry of Health.
- 1947: functions the Building Societies Acts concerning work of registrar to Treasury.
- 1948: administration of Broadmoor hospital to Board of Control.
- 1950: giving advice to local authorities on structural precautions for civil defence, to Ministry of Works.
- 1950: recommending names for minor judicial appointments to Lord Chancellor.
- 1953: regulation of slaughterhouses to Ministry of Housing and Local Government.
- 1954: regulation of markets to Ministry of Housing and Local Government.
- 1956: returns of deaths in railway accidents to Ministry of Transport and Civil Aviation in 1956.
- 1969: safety of reservoirs in England to Ministry of Housing and Local Government.
- 1971: child care responsibilities in England to Department of Health and Social Security; in Wales, to Welsh Office.
- 1973: responsibility for adoption to Department of Health and Social Security.
In the nineteenth century the Home Office retained administrative work but delegated executive duties to semi-autonomous sub-departments or external agencies responsible to Home Secretary. These included Aliens Office, State Paper Office and Signet Office. In 1836 Aliens Office and in 1851 Signet Office were absorbed in Home Office. The State Paper Office was placed under Master of the Rolls in 1852. The Home Secretary supervised General Board of Health and its successor the Local Government Act Office, and some standing commissions and in 1960 the Charity Commission. In 1963 Prison Commission was absorbed as Prison Department of the Home Office.
More directly linked with the Home Office were some inspectorates. The Factory Department and Mines Department and Fisheries, Burial Grounds, Explosives, Anatomy, Inebriates, Vivisection, Constabulary and Reformatories Inspectorates functioned as separate units. They were associated with general and later specialised administrative departments of the Home Office.
Specialised administrative departments were eg: Criminal Department, Police and Statistical Branch, Industrial Department (after 1896), Aliens Division (1904), Police Department (First World War), Children's Department and Northern Ireland Department (1924). New functions led to creation of Probation, Fire Services, Air Raid Precautions, Civil Defence, Finance, Establishment and Organisation Departments; and specialised branches eg Legal Advisor's Branch and Scientific Advisory Branch were set up.