The Postcode - we’ve all got one and you can probably remember your last few. The code is used to split the country up into sections so it’s easier to sort the post, but why was it produced and how did they pick the codes?

The postal reforms in 1840 and the rapid growth of London’s population led to a greater volume of letters. Mail was often vaguely addressed which was a particular problem in London where many streets had the same name.

In the 1850s, a committee on street names was established to consider renaming streets, but the plan did not meet with universal approval, especially not from wealthier families who lived in a street named after an ancestor. Not everyone, however, was against the changes and by the end of 1871 some 100,000 houses had been renumbered and 4,800 ‘areas’ renamed.

London postal districts

To accelerate further the delivery of mail in London, Sir Rowland Hill proposed a solution which involved dividing the capital into 10 separate postal districts. The districts would be denoted by the compass points, and an office established for each district.

  • Map breaking London up in sub-sections.

    POST 21/761. ‘London Postal District map: Showing the position of each London and Suburban Sorting Office with the Cart routes and circulation through the East and West Central Districts’ 1838.

  • The original 10 districts – EC (Eastern Central), WC (Western Central), and then NW, N, NE, E, SE, S, SW, and W – were contained within a circle of 12 miles’ radius from central London. The public were asked to add the districts’ initials to the end of an address.

    What did it actually do?

    Hill’s plan was authorised in 1856 and implemented during 1857 and 1858. The scheme accelerated the circulation of London’s mail, particularly local letters which could now be sorted in the local office instead of having to be taken to the Chief Office in the centre of London. In 1866, following a report by Surveyor Anthony Trollope (better known today as a novelist) NE was not considered viable and was merged with E district. Two years later, S was abolished, and divided between SE and SW.

Regional districts

In the 1860s London was followed by other large towns. The initial of the town name was used (M for Manchester, and S for Sheffield for example) followed by a number to indicate the geographical district. Liverpool was the first provincial town to be divided into districts: Western, Eastern, Northern and Southern districts were created in 1864/65. Manchester followed with eight districts in 1867/68, and by the early 1930s, Dublin, Sheffield, Birmingham, Bristol, Edinburgh, Glasgow, Leeds, Newcastle and Brighton had joined the scheme.

Numbering of sub-districts

Photograph of numerous women sat in rows sorting letters.

POST 118/18728 Mount Pleasant Sorting Office: Letter sorting (women) c.1914

During the First World War, the London system was further refined by dividing the districts into sub-districts, still in use today. These were introduced to assist temporary staff who had taken over the sorting work from employees who had joined the armed services. They had less knowledge of the districts than the longer serving staff they replaced. The sub-districts were each given a serial number (such as SW6 for Fulham). These formed a suffix to the district’s initials and were allocated in sequence. For example the Eastern District Office was E1, Bethnal Green was E2, Bow was E3, and so on.

Numbering outside London

In 1923, Glasgow became the first provincial city to adopt district numbering as well as district initials (G1, G2, G3, for example). However, the scheme had limited success due to few people using the district numbers.

  • In 1931, the Postmaster’s Surveyors of Leeds, Edinburgh, Newcastle, Bristol, Manchester, Liverpool, Belfast and Sheffield were asked to propose schemes for dividing the cities into numbered districts, provided they had support from local authorities. In January 1932, the proposals were approved by the Postmaster General and greater efforts were made to publicise the new districts. This was particularly effective in Glasgow and Leeds where all street signs were replaced with ones bearing the numbers.

  • Poster encouraging people to use Postal District Numbers for big cities.

    POST 110/3202. Poster promoting the use of postal district numbers. Designed by Frank Newbould and Printed by Jordison and Company Ltd.

Postcode trials

Due to the growth in mail volumes after the Second World War, it was realised that a nationwide postcoding scheme was required to enable mail to be sorted automatically by machine.

The first postcodes were introduced on a trial basis in Norwich in 1959 with the first three characters of the code (‘NOR’) representing the name of the city, and the last three characters a particular street. Larger firms and businesses received their own individual codes. Norwich had eight new sorting machines which were adapted so that operators could simply key in the postcode to sort letters to the postmen’s delivery rounds.

However, the trial was not as successful as expected. Less than half of all letters posted bore codes, and it was found that greater division of the last three characters was needed.

Leaflet with information about Norwich postal coding and illustration of the GPO man.

POST110/6043. Norwich and Postal Coding Leaflet

Introduction of the current postcode system

By the early 1960s, the Post Office had started a major mechanisation programme designed to overcome the problems of labour-intensive sorting. The introduction of mechanical sorting depended on reducing the address to a machine-readable form – a code printed on the letter in phosphor dots which could be sensed by sorting equipment. A postcode system was developed from the Norwich trials, and the present system was introduced at Croydon in 1966. The task of coding the whole country was carried out in stages, and was finally completed in 1974 with the recoding of Norwich.

  • Poster depicting where the postcodes appear on envelopes.

    POST 110/0162. Poster, Use the postcode. You’re not properly addressed without it!

  • The current postcode consists of two main elements, the outward code (needed to sort from one town to another) and the inward code (required to sort within the town).

    Taking the postcode PO1 3AX, the outward code PO1 divides into the Area PO (of which there are 121 in the UK) and the District 1 (there being approximately 20 postcode districts in an area).

    The inward code 3AX divides into the Sector 3 (with approximately 300 addresses in a sector) and the Unit AX (with about 15 addresses per unit).


Optical Character Recognition

In 1985, after successful trials at Mount Pleasant, the Optical Character Recognition (OCR) system was introduced nationally. This system automatically reads the postcode on printed addresses and prints the appropriate phosphorescent dots (codes) on to the envelope. It replaces the need for an operator to key in the postcode, and can handle letters at a much greater rate than a coding desk operator.

Video Coding

Later, the concept was to create equipment which could combine all the necessary processes into one machine. Video coding was introduced to a number of Mail Centres in combination with OCR. Images of mail ‘pieces’ which were not able to be read by OCR received codes from operators by video link elsewhere in the same office. This led to more than 95% of UK mail being coded by these means. In 1995 a 4-State code was introduced where the postcode was printed in vertical bars made up of small dots, in pink rather than blue ink.

  • Integrated Mail Processors

    Integrated Mail Processors or IMPs were introduced in 1997 to improve the complete processing system. One machine now processes the mail from arrival in the Mail Centre to dispatch by road, rail or air. It does everything – culling, facing, coding, sorting and cancelling the mail. Today, Address Interpretation technology adds to this. Images of all mail which cannot be coded instantly by OCR are then transmitted to another location (a Manual Data Entry Centre) and this eliminates local video coding.

  • A black and white photograph of a camera viewing the text written on the front of a envelope.

    POST 118/17518. This computer-controlled electronic ‘magic eye’ enables highly advanced machines to ‘read’ type-written addresses on envelopes at speeds of up to 35,000 per hour.

Sources from the collection

POST 30: England & Wales Minutes (1792-1920)

POST 33: General Minutes (1921-1954)

Postmaster General’s Reports to Parliament.

Post Office Background Information Number 12, 1984.

Clarke, L. 1993. The Power of the Postcode.

British Philatelic Bulletin Vol. 30, No.7: 164-166.

Raper, R., Rind, D. & Shepherd, J. 1992. Postcodes: The New Geography.

Glendinning, V. 1992. Trollope.

Royal Mail Annual Report 1999/2000