Postcodes in the United Kingdom

Postal codes used in the United Kingdom are known as postcodes (originally postal codes).^[1] They are alphanumeric and were introduced by the GPO (Royal Mail) over a 15-year period from 11 October 1959 to 1974.^[2] A full postcode is known as a "postcode unit" and usually corresponds to a limited number of addresses or a single large delivery point.^[1]

Postcodes have been adopted for a wide range of purposes in addition to aiding the automated sorting of the mail: for calculating insurance premiums, designating destinations in route planning software, and as the lowest level of aggregation in census enumeration. Postcode data is stored, maintained and periodically updated in the Postcode Address File database, with the full address data for around 29 million delivery points.^[1]

An earlier system of postal districts was implemented in London and other large cities from 1857. In London this system was refined in 1917 to include numbered subdivisions, extending to the other cities in 1934. These earlier districts were later incorporated into the national postcode system.

History [edit]

Earlier postal districts [edit]

London

The London post town covers 40% of Greater London. In 1857/8 it was divided into ten postal districts: EC (East Central), WC (West Central), N, NE, E, SE, S, SW, W, and NW. The S and NE sectors were later abolished and in 1917, as a wartime measure to improve efficiency, the districts were subdivided with a number applied to each sub-district, with the area served directly by the district head office as "1", then allocating the other numbers alphabetically by delivery office, e.g. N2 East Finchley, N3 Finchley, N4 Finsbury Park.

Some older road signs in Hackney still indicate the North East (NE) postal district today.

Other large towns

Street name signs on Birdbrook Road, Great Barr, Birmingham, showing old "Birmingham 22" (top) and modern "B44" postcodes.

Following the successful introduction of postal districts in London, the system was gradually extended to other large towns. Liverpool was divided into Eastern, Northern, Southern and Western districts in 1864/65, and Manchester and Salford into eight numbered districts in 1867/68.^[3]

In 1917 Dublin was 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 (C, W, NW, N, E, S, SW, SE).^[3]

In January 1932 the Postmaster General approved the division of a number of large towns into numbered districts.^[3] In November 1934 the Post Office announced the introduction of the districts 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.^[4] 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. In addition, businesses were issued with a free booklet containing maps and listings of the correct district number for every street in the ten areas.^[5]

The ten areas were:^[5]

For example, Toxteth was Liverpool 8. 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,^[6] as can still be seen on many older street-name signs.

The modern postcode system [edit]

The Post Office experimented with electromechanical sorting machines in the late 1950s.^[7] 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.^[8] 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.^[9] 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.^[10] 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).^[11]

In October 1965 it was confirmed that postal coding was to be extended to the rest of the country in the "next few years".^[12] On 1 May 1967 postcodes were introduced in Croydon. The codes for central Croydon started with the three letters CRO, and those of the surrounding post towns with outward codes (the characters before the space) of CR2, CR3 and CR4 - the last three characters, after the space, are known as the inward code. This was to be the beginning of a ten-year plan, costing an estimated £24 million. Within two years it was expected that 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.^[13] By 1967 codes had been introduced to Aberdeen, Southampton, Brighton and Derby.^[14] In 1970 codes were introduced to the London Western and North Western postal districts.^[15] In December 1970 Christmas mail was franked with the message "Remember to use the Postal Code", although codes were used to sort mail in only a handful of sorting offices.^[16]

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 (whose role superseded that of Postmaster General in 1969), Sir John Eden, stated that it was expected to be completed during 1972.^[17] 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 (district zero).^[3] The central Newport area was originally allocated NPT, in a similar way to Norwich and Croydon, with the surrounding areas allocated NP1–NP8. This lasted until the end of 1984 when, NPT being non-standard and too similar to NP7, it was recoded NP9.^[18] Girobank's GIR 0AA, the last domestic postcode with an alphabetical outward code, no longer exists in the Royal Mail's PAF system,^[19] but remains in active use by the bank's owners, currently Santander UK.^[20]

Adaptation of earlier systems into national system

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, etc. In other cases, the district numbers were replaced with new unrelated numbers. The old coding lives on in a small number of street signs with "Salford 7" etc., at the bottom. In Glasgow C1 became G1, W1 became G11, N1 became G21, E1 became G31, S1 became G41, SW1 became G51, and so on. In London the 1917 postal districts mapped directly to the new postcode districts. The remaining 60% of Greater London was allocated postcodes under the national plan.

GB postcodes available as Open data

Prior to 1 April 2010 the Royal Mail licensed use of the postcode database for a charge of about £4000 per year.^[21] Following a campaign and a government consultation in 2009^[22] the Ordnance Survey released Code-Point Open, detailing every postcode in Great Britain together with a geo-code for re-use free of charge under an attribution-only licence Open Government Licence as part of OS OpenData.

Formatting [edit]

Map of postcode areas in the United Kingdom and Crown dependencies, with links to each postcode area

The postcodes are alphanumeric and between five and eight characters long, plus a single space separating the outward and inward parts of the code. Each postcode unit generally represents a street, part of a street, or a single address.

The 'outward' part identifies first the postcode area, using one or two letters (for example L for Liverpool, RH Redhill and EH Edinburgh). A postal area may cover a wide area, for example RH covers north Sussex, which has little to do with Redhill historically apart from the railway links, and Belfast (BT) covers the whole of Northern Ireland. These letter(s) are followed by one or two digits (and sometimes a final letter) to identify the appropriate postcode district (for example W1A, RH1, RH10 or SE1P). All, or part, of one or more postcode districts are grouped into post towns.^[23] Larger post towns may use more than one district, – for example Crawley uses both RH10 and RH11. In a minority of cases a single number can cover two post towns - for example, the WN8 district includes Wigan and Skelmersdale post towns. Some 'non-geographic' outward codes are used for purposes that are not associated with any particular location.

The 'Inward' is used to assist with the delivery of post within a postal district. The first character is a number denoting a 'sector' and the final two letters identify the postcode unit, which may be a group properties, a single property, a sub-section of the property, an individual organisation or (for instance Driver and Vehicle Licensing Agency) a subsection of the organisation.^[24] The level of discrimination is often based on the amount of mail received by the premises or business.

The term "postcode district" is ambiguous in common usage, as it may refer either collectively to all the alphabetical and non-alphabetical parts in a (former) district, or only to one such part. For example, a reference to N1 might be intended either to include or to exclude N1C and N1P, depending on context, and N1C might be said to be a district or (loosely) part of the N1 district.^{[citation needed]}

Validation [edit]

The format is as follows, where A signifies a letter and 9 a digit:

Notes:

• Areas with only single-digit districts: BR, FY, HA, HD, HG, HR, HS, HX, JE, LD, SM, SR, WC, WN, ZE.
• Areas with only double-digit districts: AB, LL, SO.
• Areas with a district '0' (zero): BL, BS, CM, CR, FY, HA, PR, SL, SS (BS is the only area to have both a district 0 and a district 10).
• The following central London single-digit districts have been further divided by inserting a letter after the digit and before the space: EC1–EC4 (but not EC50), SW1, W1, WC1, WC2, and part of E1 (E1W), N1 (N1C and N1P), NW1 (NW1W) and SE1 (SE1P).
• The letters QVX are not used in the first position.
• The letters IJZ are not used in the second position.
• The only letters to appear in the third position are ABCDEFGHJKSTUW.
• The only letters to appear in the fourth position are ABEHMNPRVWXY.
• The final two letters do not use the letters CIKMOV, so as not to resemble digits or each other when hand-written.
• Post code sectors use digits from 1 to 9 followed by 0 (the Royal Mail originally sorted sector 0 after 9, treating it as the 10th not the 1st sector label).

A postcode can be validated against a table of all 1.7 million postcodes in Code-Point Open. The full delivery address including postcode can be validated against the Royal Mail Postcode Address File (PAF) which lists all 29 million valid delivery addresses.^[25]

Special cases [edit]

Crown dependencies [edit]

The Channel Islands and the Isle of Man established their own postal administrations separate from the UK in 1969. Despite this they adopted the UK format postcodes, Guernsey in 1993 using GY, the Isle of Man the same year using IM, and Jersey in 1994 using JE.^[26]

Overseas territories [edit]

Some of the UK's overseas territories have their own postcodes:

These were introduced because mail was often sent to the wrong place, e.g., for St Helena to St Helens, Merseyside^[31] and Ascension Island to Asunción, Paraguay, and, many online companies would not accept addresses without a postcode. Mail from the UK continues to be treated as international, not inland, and sufficient postage must be used. Royal Mail's Heathrow centre collects all live underpaid mail for surcharging, and there is a reciprocal arrangement with postal services around the world to collect. An agreed payment based on volumes is made, year on year. Other forms of postage are collected at local mail centres, but Heathrow collects those that still get forwarded to them. Bermuda, the UK's most populous remaining overseas territory, has developed its own postcode system, with unique postcodes for street and PO Box addresses,^[32] as have the Cayman Islands^[33] and the British Virgin Islands.^[34] Montserrat and Gibraltar do not have postcodes, although a system has been under consideration in Gibraltar.^[35] Postcodes are not used in the Turks and Caicos Islands and the TKCA 1ZZ designation is generally unknown.

British Forces Post Office (BFPO) [edit]

The British Forces Post Office (BFPO) provides a postal service to HM Forces separate from that provided by Royal Mail in the United Kingdom, with BFPO addresses used for the delivery of mail in the UK and around the world. BFPO codes such as "BFPO 801" serve the same function as postal codes for civilian addresses, with the last line of the address consisting of "BFPO" followed a space and a number of 1 to 4 digits.

For consistency with the format of other UK addresses, in 2012 BFPO and Royal Mail jointly introduced an optional alternative postcode format for BFPO addresses, using the new non-geographic postcode area "BF" and the notional post town "BFPO". Each BFPO number is assigned to a postcode in the standard UK format, beginning "BF1". The database was released commercially in March 2012 as part of the Royal Mail Postal Address File (PAF).^[36][37] A postcode is not required if the traditional "BFPO nnnn" format is used.

Non-geographic codes [edit]

Most postcodes apply to a geographic area but some are used only for routing and cannot be used for navigation or distance-finding.^[38] They are often used for direct marketing and PO boxes. Some postcode sectors or districts are set aside solely for non-geographic postcodes, including EC50, BS98, BT58, IM99, M60, N1P, NE99, SW99 and JE4.

Girobank's headquarters in Bootle uses the non-geographic postcode GIR 0AA. Non-geographic postcode area BX is used solely for non-geographic addresses, with codes independent of the location of the recipient. Prominent users include Lloyds TSB^[39] and HM Revenue and Customs.^[40] There is a special postcode for letters to Father Christmas, SAN TA1.^[41]

Special postcodes [edit]

Postcodes are allocated by Royal Mail's Address Management Unit and cannot be purchased or specified by the recipient. However, Royal Mail sometimes assigns semi-mnemonic postcodes to high profile organisations.^[42]

Prominent examples include:

Operation [edit]

Sorting [edit]

Postcodes are used to sort letters to their destination either manually, where sorters use labelled frames, or increasingly with letter-coding systems, where machines assist in sorting.^[52] A variation of automated sorting uses optical character recognition (OCR) to read printed postcodes, best suited to mail that uses a standard layout and addressing format.^[53]

A long string of "faced" letters (i.e. turned to allow the address to be read) is presented to a keyboard operator at a coding desk, who types the postcodes onto the envelopes in coloured phosphor dots. The associated machine uses the outward codes in these dots to direct bundles of letters into the correct bags for specific delivery offices. With a machine knowledge of the specific addresses handled by each postal walk at each office, the bundles can be further sorted using the dots of the inward sorting code so that each delivery round receives only its own letters.^[54] This feature depends upon whether or not it is cost effective to second-sort outward letters, and tends to be used only at main sorting offices where high volumes are handled.^[52] When postcodes are incomplete or missing, the operator reads the post town name and inserts a code sufficient for outward sorting to the post town where others can further direct it. The mail bags of letter bundles are sent by road, air or train, and eventually by road to the delivery office.^[52] At the delivery office the mail that is handled manually is inward sorted to the postal walk that will deliver it, and it is then "set in", sorted into the walk order that allows the deliverer the most convenient progress in the round.^[52][54] The latter process is now being automated, as the rollout of walk sequencing machines continues.^[55][56]

Integrated Mail Processors

Integrated Mail Processors (IMPs) read the postcode on the item and translate it into two phosphorous barcodes, unique to the inward and outward parts of the postcode, which the machines subsequently print and read, to sort the mail to the correct outward postcode. Letters may also be sequentially sorted by a CSS machine reading the outward postcode, in the order that a walking postman/woman will deliver, door to door. On such items the top phosphorous barcode is the inward part of the code, the bottom is the outward.^{[citation needed]}

IMPs can also read RM4SCC items, as used in Cleanmail, a different format to the above.

Mailsort

A newer system of five-digit codes called Mailsort has been designed for users who send 'a minimum of 4,000 letter-sized items.'^[57] It encodes the outward part of the postcode in a way that is useful for mail routing, so that a particular range of Mailsort codes goes on a particular plane or lorry. Mailsort users are supplied with a database to allow them to convert from postcodes to Mailsort codes and receive a discount if they deliver mail to the post office split up by Mailsort code. Users providing outgoing mail sorted by postcode receive no such incentive since postcode areas and districts are assigned using permanent mnemonics, and do not therefore assist with grouping items together into operationally significant blocks.

Licensing and availability [edit]

Life-cycle of post codes [edit]

There are also significant numbers of discontinued (terminated) codes. Each month some 2,750 postcodes are created and 2,500 terminated.^[58]

Postcode Address File (PAF) [edit]

The Postcode Address File (PAF) is commercially licenseable and is often incorporated in address management software packages. The capabilities of such packages allow most addresses to be constructed solely from the postcode and house number. By including the map references of postcodes in the address database, the postcode can be used to pinpoint a postcode area on a map. PAF is updated monthly.^{[citation needed]}

Code-Point Open [edit]

Since 1 April 2010 an Ordnance Survey geo-coded file containing every postcode in Great Britain has been available for re-use without charge under an attribution-only licence, as part of OS OpenData.

Other uses of postcodes [edit]

This section requires expansion. (December 2009)

While postcodes were introduced to expedite the delivery of mail, they are useful tools for other purposes, particularly because codes are very fine-grained and identify just a few addresses. Among uses are:

• Finding the nearest branch of an organisation to a given address. A computer program uses the postcodes of the target address and the branches to list the closest branches in order of distance as the crow flies (or, if used in conjunction with streetmap software, by road distance). This can be used by companies to inform potential customers where to go, by job centres to find jobs for job-seekers, to alert people of town planning applications in their area, and a great many other applications.^[21]
• With satellite navigation systems, to navigate to an address by street number and postcode.
• By non-life insurance companies to assess premiums for motoring/business/domestic policy premiums.
• By life insurance companies and pension funds to assess longevity for pricing and reserving.^[62]

See also [edit]

• List of postcode areas in the United Kingdom
• List of postal codes (around the world)
• ACORN
• Address Point
• Postcode lottery
• RM4SCC—a machine-readable barcode version of the postcode

References [edit]

External links [edit]

• Royal Mail has two ways to search addresses or postcodes from its website, allowing up to 15 searches a day free of charge (these cover nearly all UK and crown dependency postcodes but not the non-geographic BX postcode area nor "GIR 0AA"):
  • Royal Mail's Online Postcode Finder (for the postcode for a specified street or address)
  • Royal Mail's Online Address Finder (for addresses covered by a specified postcode)
• BFPO Locations (BFPO locations, numbers and postcodes)
• Beacon Dodsworth: Postcode updates
• Universal Postal Union: United Kingdom of Great Britain and Northern Ireland
• Free Postcode Lookup (Free street level postcode API provider, using own in-house database)