Before the 19th century there were no nationally organised police services. Traditionally, householders served one year as constable or night watchman for their communities. Constables apprehended people accused of crimes and brought them before a justice of the peace. Night watchmen patrolled the streets from evening until sunrise. Both were responsible for keeping the peace but not for investigating or prosecuting crimes.

In the eighteenth century thief-takers used their knowledge of the criminal underworld to earn rewards for catching suspects. Magistrates Henry and John Fielding established the Bow Street Runners at their Westminster courthouse in 1749. Although effective they only covered part of London and in 1839 they merged with the Metropolitan Police.

By the 1800s London’s increasing population and rising crime levels overwhelmed local policing. Demands for tougher law enforcement also raised concerns about greater police powers affecting citizens’ rights. In 1829 Home Secretary Sir Robert Peel established the Metropolitan Police. Initially they covered a seven-mile radius from Charing Cross but excluding the City of London, where the City Marshall and beadles provided daytime patrols and a night watch. In 1839 these were replaced by the separate City of London Police.

During the First World War female volunteers formed a Women’s Police Service, but women only entered the Metropolitan Police from 1919. Their ranks and pay were lower than male colleagues and their roles were limited. 1923 saw female officers gain powers of arrest and wider career choices, but they only achieved full integration and equal pay in the 1970s.

In addition to the Metropolitan and City Police forces other police bodies have operated across Greater London, including British Transport Police, Royal Parks Constabulary and Thames River Police. From the mid-nineteenth century police duties have continually expanded to reflect the growing complexity of society and now include forensics, fraud, and cybercrime.