A division was until recently the largest territorial subdivision of most British Police forces, similar to a precinct in American city police departments.
The term has existed since the creation of police forces in the early 19th century. Most police forces were divided into divisions, usually commanded by a superintendent. These could cover a wide rural area, a substantial town, or a portion of a city, depending on the population (London, for instance, was divided at one point into 67 Metropolitan Police divisions and a further four City of London Police divisions). In 1949 the Metropolitan Police regraded its divisional commanders as chief superintendents and most other forces followed suit.
Divisions functioned as semi-independent bodies, with the divisional commander being allowed a great deal of freedom in the way he policed his "patch". A division had its own Criminal Investigation Department (CID) officers, who handled all investigations except very specialist operations and serious crimes such as murder, for which experienced specialist officers from headquarters were called in (although the groundwork was still largely done by local CID). There was frequently great rivalry and even dislike between officers based "on the divisions" and officers based at headquarters, with the former seeing the latter as elitist fast-trackers who did not know what real police work was all about, and the latter seeing the former as unimaginative "plods" without any real ambition or ability. There was also great rivalry between adjacent divisions, which sometimes degenerated into operations deliberately designed to embarrass or discredit the other.
Major reforms of police organisation took place in the 1990s and the divisions were restructured and retitled Basic Command Units (BCUs). Some forces continue to refer to them as divisions, however.