Postcodes in the United Kingdom

Postal codes used in the United Kingdom, British Overseas Territories and Crown dependencies are known as postcodes (originally, postal codes).^[1] They are alphanumeric and were adopted nationally between 11 October 1959 and 1974, having been devised by the General Post Office (Royal Mail).^[2]

The system was designed to aid in sorting mail for delivery. It uses alphanumeric codes to designate geographic areas. A full postcode identifies a group of addresses (typically around 10) or a major delivery point. It consists of an outward code and inward code. The outward code indicates the area and district, while the inward code specifies the sector and delivery point.

The initial postcode system evolved from named postal districts introduced in London and other large cities from 1857. Districts in London were then subdivided in 1917, with each allocated a distinct number, which extended to other cities by 1934. The territory of the UK is broken down into 121 postcode areas. Each postcode area contains multiple post towns and districts. Postcode areas are mnemonically named after the area's major post town (such as TR for TRuro) although some are named after smaller towns or regional areas.

Postcodes have since been additionally used in various applications. Postcodes help calculate insurance premiums, designate destinations in route planning software, and serve as aggregation units in census enumeration. The Postcode Address File (PAF) database stores and updates the boundaries and address data for around 29 million addresses, ensuring accurate delivery and extensive utility beyond postal services.