There are a number of agencies that participate in law enforcement in the United Kingdom which can be grouped into three general types:

Territorial police forces, who carry out the majority of policing. These are police forces that cover a police area (a particular region) and have an independent police authority. Current police forces have their grounding in the Police Act 1996 (in England and Wales), the Police and Fire Reform (Scotland) Act 2012 (in Scotland) and the Police (Northern Ireland) Act 2000 (in Northern Ireland), which prescribe a number of issues such as appointment of a chief constable, jurisdiction and responsibilities. National law enforcement bodies, including the National Crime Agency and national police forces that have a specific, non-regional jurisdiction, such as the British Transport Police. The Serious Organised Crime and Police Act 2005 refers to these as 'special police forces', not including the NCA which is not a police force. In addition, there are non-police law enforcement agencies, whose officers are not police officers, but still enforce laws, and other bodies with solely investigatory powers. Miscellaneous police bodies, mostly having their foundations in older legislation or common law. These are responsible for policing specific local areas or activities, such as ports and parks. Before the passing of recent legislation such as the Serious Organised Crime and Police Act 2005, they were often referred to as 'special police forces'; care must therefore be taken in interpreting historical use of that phrase. These constabularies are not within the scope of the legislation applicable to the previously mentioned organisations but can still be the subject of statutes applicable to, for example, docks, harbours or railways. Until the passing of the Railways and Transport Safety Act 2003, the British Transport Police was such a force.

Most law enforcement in the United Kingdom is carried out by territorial police forces that police the general public and their activities. The other types of agencies are concerned with policing of more specific matters.

Over the centuries there has been a wide variation in the number of police forces in the United Kingdom, with a large number now no longer in existence.

Territorial police forces

Most policing in the United Kingdom is conducted by the 45 territorial police forces of the 4 nations in one of three legal criminal jurisdictions – England & Wales, Scotland and Northern Ireland. These forces are ultimately responsible for all law and order within their respective police area (a legal term which defines the geographic area of primary responsibility). This is not the same as legal jurisdiction, see below. Two nations of the United Kingdom, Scotland and Northern Ireland, have national police forces. The third legal jurisdiction, made up of the nations of England and Wales is split up into a number of police forces. The breakdown of all territorial police forces across the United Kingdom by jurisdiction is as follows:

43 territorial police forces in England & Wales 1 territorial police force in Scotland 1 territorial police force in Northern Ireland

England and Wales

Except in Greater London, each territorial police force covers one or more of the local government areas (counties) established in the 1974 local government reorganisations (although with subsequent modifications), in an area known in statute as a police area. These forces provide most of the policing services to the public of England and Wales. These forces have been known historically as "Home Office police forces" due to the central government department, the Home Office, being responsible for and providing most of the funding these police forces. Despite the implication of the term, all police forces are independent, with operational control resting solely with the chief officer of each force (the chief constable or with regard to the Metropolitan Police and City of London Police forces, their respective Commissioners); each force was overseen by a police authority until these were replaced by police and crime commissioners in 2012.

The Police Act 1996 is the most recent piece of legislation, which outlines the areas of responsibility for the 43 territorial forces of England and Wales (found in Schedule 1 of the Act).

Constable is the lowest rank in the police service, but all officers, whatever their rank, are "constables" in terms of legal powers and jurisdiction. Police officers in territorial police forces in England and Wales derive their jurisdiction from Section 30 of the Police Act 1996. This section outlines that such officers have jurisdiction throughout England and Wales and also the adjacent United Kingdom waters. Special constables, who are part-time, volunteer officers of these forces, used to have a more limited jurisdiction – limited solely to their own force areas and adjacent forces. Since 1 April 2007, however special constables of England and Wales have full police powers throughout those two countries. This means that, in contrast to most countries, all UK volunteer police officers now have exactly the same powers as their full-time colleagues. There are a number of situations in which the jurisdiction of a constable extends to one of the other countries, and constables of one jurisdiction do have reciprocal powers of arrest in each other's jurisdictions as a matter of course see the main article for details.

England

Avon and Somerset Police Bedfordshire Police Cambridgeshire Constabulary Cheshire Constabulary City of London Police (not shown) Cleveland Police Cumbria Constabulary Derbyshire Constabulary Devon and Cornwall Police Dorset Police Durham Constabulary Essex Police Gloucestershire Constabulary Greater Manchester Police Hampshire and Isle of Wight Constabulary Hertfordshire Constabulary Humberside Police Kent Police Lancashire Constabulary Leicestershire Police Lincolnshire Police Merseyside Police Metropolitan Police Service Norfolk Constabulary Northamptonshire Police Northumbria Police North Yorkshire Police Nottinghamshire Police South Yorkshire Police Staffordshire Police Suffolk Constabulary Surrey Police Sussex Police Thames Valley Police Warwickshire Police West Mercia Police West Midlands Police West Yorkshire Police Wiltshire Police

, the police forces in England have: 124,492 police officers 8,634 special constables 8,659 police community support officers (PCSO) 7,504 police support volunteers (PSV) 76,466 staff

Wales

Dyfed-Powys Police () Gwent Police () North Wales Police () South Wales Police ()

, the police forces in Wales have: 7,274 police officers 492 special constables 834 police community support officers (PCSO) 387 police support volunteers (PSV) 4,774 staff There have also been proposals for an all-Wales police force, such as in 2006.

Collaborative units South East Counter Terrorism Unit Thames Valley & Hampshire Joint Operations Unit Surrey Police & Sussex Police Tactical Firearms, Operations Command and Roads Policing Unit South West Counter Terrorism Unit Dorset Police and Devon & Cornwall Police Strategic Alliance Unit East Counter Terrorism Intelligence Unit Norfolk & Suffolk Roads Policing Unit Bedfordshire, Cambridgeshire & Hertfordshire Road Policing Unit Bedfordshire, Cambridgeshire & Hertfordshire Major Crime Unit East Midlands Counter Terrorism Intelligence Unit West Midlands Police Counter Terrorism Unit Warwickshire Police and West Mercia Police Specialist Operations Unit North West Counter Terrorism Unit Cheshire Police & North Wales Police Alliance Armed Policing Unit North East Counter Terrorism Unit Durham and Cleveland Specialist Operations Unit Welsh Extremism and Counter Terrorism Unit Gwent Police & South Wales Police Joint Armed Response Unit

Scotland

Most police powers and functions have been inherited by the Scottish Government and Scottish Parliament from the former Scottish Office (1885–1999). Areas for which legislative responsibility remains with the UK Government include national security, terrorism, firearms and drugs. The Police (Scotland) Act 1967, as amended, was the basis for the organisation and jurisdiction of the eight former territorial forces in Scotland that were formed in 1975. These forces covered one or more of the areas of the local government regions established in the 1975 local government reorganisation (and since abolished), with minor adjustments to align with the post-1996 council area borders. These forces provided most of the police services to the public of Scotland, although Scottish police officers also have limited jurisdiction throughout the rest of the United Kingdom as required (See above comments under English and Welsh forces).

In 2011, the Scottish Government announced that it planned to amalgamate the eight territorial forces in Scotland, along with the Scottish Crime and Drug Enforcement Agency, into a single agency. The Police and Fire Reform (Scotland) Act 2012, an Act of the Scottish Parliament, codified this amalgamation and brought about the new Police Service of Scotland (to be known as "Police Scotland"). The new force was established on 1 April 2013.

In 2017, plans were being debated in the Scottish Parliament to merge railway policing with Police Scotland.

As of December 2019, police numbers in Scotland were: Police officers: 17,259 Special constables: 531 Other staff: 6,168

Community Support Officers, commonly referred to as "Police Community Support Officers", were established by Section 38(2) of the Police Reform Act 2002, which applies only to England and Wales. There are therefore no Community Support Officers in Scotland.

Northern Ireland

County and borough based police forces were not formed in Ireland as they were in Great Britain, with instead a single Royal Irish Constabulary covering most of Ireland (the exceptions being the Dublin Metropolitan Police, which was responsible for policing in Dublin, and the Londonderry Borough Police and Belfast Town Police, both replaced by the RIC in the late Victorian period). The Royal Ulster Constabulary was formed in 1922 after the establishment of the Irish Free State, and served until the reforms of the police under the terms established initially by the Good Friday Agreement of 1998 undertaken by the Patten Commission, which led to dissolution of the RUC in 2001. The Police (Northern Ireland) Act 2000 sets out the basis for the organisation and function of the police force in the province. Until 2010, police powers were not transferred to the devolved Northern Ireland Executive, unlike Scotland, instead remaining with the Northern Ireland Office. However, in January 2010 agreement was reached between the two largest parties in the Assembly, the DUP and Sinn Féin, over a course that would see them assume responsibility for policing and justice from April.What will happen when policing and justice is devolved? – BBC News, 05/02/10

As of April 2007 police numbers in Northern Ireland were:APA Police Service Strength Map Update , Association of Police Authorities, 28 August 2010. Police officers: 7,216 Full-time reserve police officers: 335 Part-time police officers: 684 Other staff: 2,265

Police in Northern Ireland do not employ Police Community Support Officers

National Collaborative Units

Bodies hosted by the National Police Chiefs' Council (NPCC) National Wildlife Crime Unit – A police unit run by the NPCC that gathers intelligence on wildlife crime and provides analytical and investigative support to law enforcement agencies across the United Kingdom. National Counter Terrorism Security Office – A police unit run by the NPCC, which advises the British government on its counter terrorism strategy. National Vehicle Crime Intelligence Service – A police unit run by the NPCC, tasked with combating organised vehicle crime and the use of vehicles in crime.