Covert policing in the United Kingdom
Covert policing in the United Kingdom is employed to enable an officer of the British police to gather intelligence from and about suspects without alerting them that they are under observation. == History == Much of Britain's police service throughout the early to mid-20th century consisted of police officers walking a beat, one in each neighbourhood.
Source: Wikipedia — Covert policing in the United Kingdom (CC BY-SA 4.0)