Postcodes in the United Kingdom
From Wikipedia, the free encyclopedia
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] A full postcode is known as a "postcode unit" and designates an area with several addresses or a single major delivery point.[1]
This article's lead section may be too long. (May 2021) |
The structure of a postcode is two alphanumeric codes that show, first, the Post Town and, second, a small group of addresses in that post town. The first alphanumeric code (the Outward code or Outcode) has between two and four characters and the second (the Inward Code or Incode) always has three characters. The Outcode indicates the postcode area and postcode district. It consists of one or two letters, followed by one digit, two digits, or one digit and one letter. This is followed by a space and then the Incode which indicates the postcode sector and delivery point (usually a group of around 15 addresses, but sometimes more). The incode (always three characters), starts with a number (denoting a sector within the district), and ends with two letters (denoting delivery points which are allocated to streets, sides of a street or individual properties). Postcode areas are usually, but not always, named after a major town or city — such as B for Birmingham. Some after named a smaller town (e.g. Southall postcode area is UB after Uxbridge) or a combination of towns (e.g. SM appears to be named after Sutton and Morden). A small number are geographic in nature — such as HS for the Outer Hebrides, FY for Fylde (the region around Blackpool) and ME for the Medway connurbation, with Rochester as its main post town. In the case of London (a Post Town), there is not a single "London" postcode area; rather there are eight (N,E,EC,SE,SW,W,WC and NW) reflecting the preceding system for coding London based on compass points. In the case of Northern Irleand, the entire nation has a single postcode area BT (based on Belfast BT). Post codes generally do not align with historical county or local authority boundaries.
Each postcode area contains a number of post towns and postcode districts. Example: a sizeable part of southern England is covered by the GU postcode area, named after the town of Guildford. Guildford itself consists of postal districts GU1 and GU2. Nearby Woking, a major commuter town—10km away—is a post town within the postcode district GU22.
As a general rule, the central part of the town/city the postcode area is named after will have the number 1 e.g. B1 (Birmingham) - but there a limited number of postcode areas that start 0 or 10, eg. SL0 and AB10. Large post towns are generally numbered from the centre outward such that outlying parts have higher numbered districts.
Alternatively, but less commonly, post towns and postcode districts within the area may be numbered according to: geographical direction (e.g. the Outer Hebrides area HS, the districts are numbered from north to south); alphabetical order of district sub-offices (particularly in London (e.g. E2 is Bethnal Green, E3 is Bow, E4 is Chingford etc.); and clusters, particularly if the postcode area encompasses several major towns or cities (e.g. S postcode area with Sheffield S1-S36, Chesterfield S40-S49, Rotherham S60-S65, Barnsley S70-S75 and Worksop S80-S81). Accordingly, the centrality of a postcode district within a postcode area cannot be reliably inferred from the postcode alone (e.g. SE1 covers a large part of Central London south of the Thames whereas SE2 covers Abbey Wood at the far eastern end of the Elizabeth Line). See postcode area.
Numbering of postcode districts is normally consecutive, but this is not universal. Non-consecutive numbering arises when districts are numbered for geographical and/or clustering reasons (e.g. PH postcode area's highest numbered district is PH50 but, within the range of PH1-PH50, the numbers PH27-PH29 and PH45-PH48 are not allocated, so as to maintain a distinct geographical link for each group of allocated numbers).
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 route planning software and as the lowest level of aggregation in census enumeration. The boundaries of each postcode unit and within these the full address data of currently about 29 million addresses (delivery points) are stored, maintained and periodically updated in the Postcode Address File database.[1]
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.
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.[3]