Postcodes in the United Kingdom
The structure of a postcode is two alphanumeric codes, the first having between two and four characters and the second, three characters. First, one or two letters indicate the postcode area, followed by one or two digits signifying a district within that area. This is followed by a space and then a number denoting a sector within said district, and finally by two letters which are allocated to streets or sides of a street. Postcode areas are often named for a major town or city (such as B for Birmingham) but may also be geographic in nature (such as HS for Outer Hebrides).
Each postcode area contains a number of post towns which are not themselves alphabetically denoted however each will generally constitute one (or more) postcode districts. (Example: a sizeable part of Southern England is covered by the GU postcode area, named for the town of Guildford. Guildford comprises postal districts GU1 and GU2. Nearby Woking, a major commuter town 6 miles distant, is a post town within postal district GU22.) The central part of the town or city the postcode area is named after will have the number one e.g. B1 (Birmingham), LS1 (Leeds), M1 (Manchester), however other post towns within the area are then either treated alphabetically - particularly in London (e.g. Chingford on the north-eastern edge of London being E4, whereas adjacent Walthamstow to the south being E17) or geographically (e.g. the Outer Hebrides area HS numbering the districts north to south).
As a general rule, large post towns are numbered from the centre out such that outlying parts have higher numbered districts, but the disparate post towns within a postal area can be numbered based on various criteria (the town the postal area is named after excepted, this always being 1). In particular, one cannot reliably infer the centrality of a postcode district within a postcode area from the postcode alone, as for instance SE1 covers a large part of Central London south of the Thames whereas SE2 covers Abbey Wood at the far end of the Elizabeth Line. See
Postcodes have been adopted for a wide range of purposes in addition to aiding the sorting of mail: for calculating insurance premiums, designating destinations in
The initial system of named postal districts, developed in London and other large cities from 1857, evolved towards the present form: in 1917 London was split into broad numbered subdivisions, and this extended to the other cities in 1934. Since the local government reorganisation of London in the 1960s, parts of
As examples of the postcode system, the postcode of the
Theoretically, deliveries can reach their destination using the house number (or name if the house has no number) and postcode alone; however, this is against Royal Mail guidelines, which request the use of a full address.
The London post town covers 40% of
Some older road signs in Hackney still show the North East (NE) sector/district.
Following the successful introduction of postal districts in London, the system was extended to other large towns and cities. Liverpool was divided into Eastern, Northern, Southern and Western districts in 1864/65, and Manchester and Salford into eight numbered districts in 1867/68.
In 1917, Dublin—then still part of the United Kingdom—was divided into
In January 1932 the Postmaster General approved the designation of some predominantly urban areas into numbered districts. In November 1934 the Post Office announced the introduction of numbered districts (short postal codes) in "every provincial town in the United Kingdom large enough to justify it". Pamphlets were issued to each householder and business in ten areas notifying them of the number of the district in which their premises lay. The pamphlets included a map of the districts, and copies were made available at local head post offices. The public were "particularly invited" to include the district number in the address at the head of letters.
A publicity campaign in the following year encouraged the use of the district numbers. The slogan for the campaign was "For speed and certainty always use a postal district number on your letters and notepaper". A poster was fixed to every pillar box in the affected areas bearing the number of the district and appealing for the public's co-operation. Every post office in the numbered district was also to display this information. Printers of Christmas cards and stationery were requested to always include district numbers in addresses, and
The ten areas were:
The Post Office experimented with electromechanical sorting machines in the late 1950s. These devices presented an envelope to an operator, who would press a button indicating which bin to sort the letter into. Postcodes were suggested to increase the efficiency of this process by removing the need for the sorter to remember the correct sorting for as many places. 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
On 1 May 1967 postcodes were introduced in
During 1971, occupants of addresses began to receive notification of their postcode. Asked in the House of Commons about the completion of the coding exercise, the
A quirk remained: the central Newport (Gwent) area was allocated NPT at a similar time to Croydon becoming CRO, and surrounding areas were (as today) allocated NP1–NP8. NPT lasted until the end of 1984 when it was recoded NP9.
When the national postcode system was introduced, many existing postal districts were incorporated into it, so that postcodes in Toxteth (Liverpool 8) start with L8. The districts in both Manchester and Salford gained M postcodes, so Salford 7 became M7 and so on (and similarly in Brighton and Hove, both using the prefix BN). The old coding lives on in a small number of street signs with (for example) "Salford 7" at the bottom. In other cases, the district numbers were replaced with unrelated numbers. In Glasgow many of its G-prefixed numbers are not used as C1 became G1, W1 became G11, N1 became G21, E1 became G31, S1 became G41, SW1 became G51, and so on. In London (as postally defined), 1917-created postal districts are mapped unchanged to those of today but its much enlarged administrative area, Greater London, was created in April 1965. From that month the remaining 60% of Greater London's area has postcodes referring to 13 other post towns. Additionally, there were too few postcodes to adequately cover districts in central London (particularly in the WC and EC areas), so these were subdivided with a letter suffix rather than being split into new numbered districts so as to retain the familiar codes.
Prior to 1 April 2010, the Royal Mail licensed use of the postcode database for a charge of about £4000 per year. Following a campaign and a government consultation in 2009, the Ordnance Survey released Code-Point Open, detailing each current postcode in Great Britain together with a geo-code for re-use free of charge under an attribution-only licence (