Postal codes used in the United Kingdom are known as postcodes (originally postal codes). They are alphanumeric and were adopted nationally between 11 October 1959 and 1974, having been devised by the GPO (Royal Mail). A full postcode is known as a "postcode unit" and designates an area with a number of addresses or a single major delivery point.
In January 1959 the Post Office analysed the results of a survey on public attitudes towards the use of postal codes, choosing a town in which to experiment with codes. The envisaged format was a six-character alphanumeric code with three letters designating the geographical area and three numbers to identify the individual address. On 28 July Ernest Marples, the Postmaster General, announced that Norwich had been selected, and that each of the 150,000 private and business addresses would receive a code by October. Norwich had been selected as it already had eight automatic mail sorting machines in use. The original Norwich format consisted of "NOR" followed by a space, then a two-digit number (which, unlike the current format, could include a leading zero) and a single final letter (instead of the two final letters in the current format).
In October 1965, Tony Benn as Postmaster General announced that postal coding was to be extended to the rest of the country in the next few years.