Prior to the mid-19th century, there was not a policing system. Citizens were responsible for their own protection and prosecution, having to conduct their own investigations following a crime. Unofficial policing took the form of self-defense, private individuals (Thief Takers) offering their services, and parishes organizing voluntary watch.

The keepers of law and order included Night Watchmen (originated in 13th c. as volunteers but formalized in 17th century) and Parish Constables. Their positions were part-time, and those in place were typically older and often infirm. If an arrest was made, the offender would be brought before the nearest Magistrate (the unpaid official chosen among the ranks of the wealthiest locals) for quick conviction of petty crimes, or in the case of felony crimes brought before the Circuit Court/Crown Court during the Quarterly Assizes in large towns or the Old Bailey in London.

In 1750, Sir Henry Fielding (yes, the author) developed an unofficial policing force based from his own home on Bow Street in Covent Garden. While start-up was grant funded, the maintenance costs were out of pocket, the Fielding brothers conducting all training, record keeping, publicizing, etc., including publishing a journal and newspaper to apprise citizens of crimes, criminals at large, stolen goods, etc. The runners were the first effective law enforcement, focused on investigating crimes and finding criminals who had fled the scene. There were up to 68 runners in London by 1800.

Based on the runners, in 1829, Sir Robert Peel, Home Secretary, proposed a bill to establish a Metropolitan Police Force, thus beginning the reign of the "Bobbies" and the eventual development of the first detective dept in 1842 and establishment of Scotland Yard.

Check out these two resources to learn more:

Historic UK: Bow Street Runners

British Library: Crime and Punishment in Georgian England