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), a combination of Police (Scotland) Act 1967 and 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 forces, 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 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.