Postcodes in the United Kingdom
s used in the United Kingdom, British Overseas Territories and Crown dependencies are known as postcodes. They are alphanumeric.
Postcodes are essentially a location specific routing instruction. The codes designate 121 geographic postcode areas which are mnemonically named after the area's major post town although some are named after smaller towns or regional areas. Each postcode area is subdivided into districts, which in turn are subdivided into sectors. A full postcode identifies a group of addresses or a major delivery point.
The current postcode system evolved from named postal districts introduced in London in 1857 and gradually in other large cities from the 1860s onwards. Districts in London were then subdivided in 1917, with each allocated a distinct number. This was extended to other cities by 1934. The current system was devised by the General Post Office and was adopted nationally in stages between 1959 and 1974.
The system was designed with a single objective, to aid Royal Mail in mechanised sorting of mail for delivery. Since its roll-out, changes in business needs and new technology have meant that postcodes are now also used in many differing ways: they serve as aggregation units in census enumeration; designate destinations in route planning software, and help calculate insurance premiums.
Royal Mail is statutorily responsible for allocation of all postcodes and it continuously maintains the Postcode Address File database, which stores address data for around 32 million addresses and around 1.8m postcodes. The PAF is overseen by the independent PAF Advisory Board and Ofcom, which regulates communication services in the UK.
History
Earlier postal districts
London
London was the first city in the United Kingdom to design and adopt a postal code system. On inception, London was divided into ten postal districts: EC, WC, N, NE, E, SE, S, SW, W, and NW, covering a circle with a radius of 10 miles from central London. The initials of the named districts were to be appended to the street address. In 1866 the North East district was abolished and merged into East district. In 1868, the South district was also abolished, with different parts merged into South East and South West districts. Some older road signs in Hackney still show the short-lived North East district.Other large cities and towns
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.Urban areas - numbered districts
In 1917, as a wartime measure to improve efficiency, each postal district in London was subdivided into sub-districts each identified by a number; the area served directly by the district head office was allocated the number 1; the other numbers were allocated alphabetically by delivery office, e.g. N2 East Finchley delivery office, N3 Finchley delivery office, N4 Finsbury Park delivery office etc. Since then these sub-districts have changed little.In 1917, Dublin—then still part of the United Kingdom—was similarly divided into numbered postal districts. These continue in use in a modified form by An Post, the postal service of the Republic of Ireland.
In 1923, Glasgow was divided in a similar way to London, with numbered districts preceded by a letter denoting the compass point.
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 in "every provincial town in the United Kingdom large enough to justify it". Pamphlets were issued to each householder and business in the chosen 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 election agents for candidates in the upcoming general election were asked to ensure they correctly addressed the 100 million items of mail they were expected to post. Businesses were issued with a free booklet containing maps and listings of the correct district number for every street in the ten areas.
Changes were made in towns which had already created postal districts: e.g. in Liverpool, the four compass point districts were expanded and districts were allocated numbers such as Liverpool 8 for Toxteth; a single numbering sequence was shared by Manchester and Salford: letters would be addressed to Manchester 1 or Salford 7 ; some Birmingham codes were sub-divided with a letter, such as Great Barr, Birmingham 22 or Birmingham 22a, as can still be seen on many older street-name signs.
Modern postcode system
The Post Office experimented with electro-mechanical 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, and committed to choosing a town in which to experiment with codes. The envisaged format for the new post code was a six-character alphanumeric code in two parts, with three letters designating the geographical area and three numbers identifying 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 was 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, and finally a single letter.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.
On 1 May 1967 postcodes were next introduced in Croydon. The many postcodes for central Croydon began with "CRO", while those of the surrounding post towns with CR2, CR3 and CR4. The uniform system of a set of three final characters after the space was adopted. This was to be the beginning of a ten-year plan, costing an estimated £24 million. Within two years it was expected that full coding would be used in Aberdeen, Belfast, Brighton, Bristol, Bromley, Cardiff, Coventry, Manchester, Newcastle upon Tyne, Newport, Reading, Sheffield, Southampton and the Western district of London. Newcastle upon Tyne and Sheffield were allocated NE and S respectively, which had been created originally in London, but later abolished. By 1967, codes had been introduced to Aberdeen, Southampton, Brighton and Derby. In 1970, codes were introduced to the London Western and North Western postal districts. In December 1970, much Christmas mail was postmarked with the message "Remember to use the Postal Code" although codes were used to sort mail in only a handful of sorting offices.
The original London post town covers only 40% of the administrative area of Greater London. 60% of Greater London's area has postcodes in 13 other postcode areas and post towns.
Many existing postal districts were incorporated into the new national system so that postcodes in Toxteth start with L8. The districts in both Manchester and Salford gained M postcodes, so Salford 7 became M7 and so on. In other cases, the district numbers were replaced with unrelated numbers. In Glasgow, as a result of the transposition of the earlier compass point districts to "G" districts many of the available G districts have not been allocated.
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 Minister of State for Posts and Telecommunications, Sir John Eden, stated that it was expected to be completed during 1972. The scheme was finalised in 1974 when Norwich was completely re-coded but the scheme tested in Croydon was sufficiently close to the final design for it to be retained, with CRO standardised as CR0 thus removing the need to create a CR1 district.
A quirk remained: the central Newport area was allocated NPT at a similar time to Croydon becoming CRO, and surrounding areas were allocated NP1–NP8. NPT lasted until the end of 1984 when it was recoded NP9.
Girobank's GIR 0AA was the last UK postcode with a fully alphabetical outward code. That code no longer exists in the Royal Mail's PAF, but was taken over by the bank's current owners, Santander UK.