London postcodes: why each district has the number it has

Ten districts inside a twelve-mile circle

Until 1857 London's post was sorted as if the city were one town. Rowland Hill's plan, authorised in 1856, divided it into ten districts within a circle of 12 miles' radius drawn from the General Post Office at St Martin's-le-Grand. The public was asked to end every address with the district's initials: EC, WC, N, NE, E, SE, S, SW, W or NW.

The circle covers about 1,170 km². The numbered districts of today fill about half of it: outlying places were later handed to other post towns, Ilford among them in 1867.

Why London has no S and no NE

In 1866 Anthony Trollope, a Post Office surveyor as well as a novelist, was asked to review London's collections and deliveries. He reported within three months: abolish the North Eastern district and divide the Southern between its neighbours, because they carried too little mail for what they cost. S had gone by 1868. The NE office closed in 1867, and the public was told in 1869.

NE stayed in use regardless, on street signs and on envelopes. In 1897 a group of Hackney businessmen petitioned to have the district back, objecting to being labelled “Eastern”. Only the numbers of 1917 ended it. Today NE is Newcastle upon Tyne and S is Sheffield.

The war takes the sorters, and the offices get numbers

By June 1917 more than 75,000 Post Office men had joined the Army, and 14,000 temporary substitutes were at work in London alone. A sorter had to know by heart, or look up in printed lists, which delivery office served each street.

“Before the War, the Post Office staff from long experience were able to sort the greater number of letters correctly even when they were wrongly or insufficiently addressed. But the majority of these officers are now serving in the Army…”Albert Illingworth, Postmaster-General, 1 March 1917

His remedy was a number after the initials, to “indicate the proper Office of Delivery”. A free booklet gave the new number for every principal street: 5,655 lines. Three months later he told the Commons that 40 per cent of letters carried one. The idea was older than the war: it had been suggested inside the Post Office in 1902, 1909, 1911 and 1914.

The rule the public was never told

The booklet says that the number denotes “the Office of Delivery” and gives two examples: N.W. 1 for the North-Western District Office, N.W. 3 for Hampstead. It does not say how the numbers were chosen. The method is in a Post Office file. On 5 July 1916 the Controller of the London Postal Service recommended numbering each district's offices in “the alphabetical order of the delivery offices”, with the head office as number 1. His note is quoted in Helen Kearney's 2017 thesis on the London postal map.

The list of 1917 does exactly that. In the Eastern district, number 1 is the district office and the rest run from B to W:

1. E1district office
2. E2Bethnal Green
3. E3Bow
4. E4Chingford
5. E5Clapton
6. E6East Ham
7. E7Forest Gate
8. E8Hackney
9. E9Homerton
10. E10Leyton
11. E11Leytonstone
12. E12Manor Park
13. E13Plaistow
14. E14Poplar
15. E15Stratford
16. E16Victoria Docks and North Woolwich
17. E17Walthamstow
18. E18Woodford and South Woodford
19. E20Olympic Park

* added after 1917

So Chingford, the most northerly of them, is E4, and Walthamstow beside it is E17.

Outside the centre, 101 offices in the list follow a district office. All 101 are in alphabetical order.

Twenty-one names, sorted letter by letter

East Finchley is N2 and Wood Green is N22. Lower Edmonton is N9; Upper Edmonton, next door, is N18.

Southgate (N14) comes before South Tottenham (N15). Whoever numbered them ignored the space and sorted letter by letter: S-o-u-t-h-g before S-o-u-t-h-t.

NW9 is filed under T

NW9 is Colindale, Kingsbury and West Hendon. In 1917 its delivery office was The Hyde, on the Edgware Road, and it was filed under T: after St John's Wood (NW8) and before Willesden (NW10).

1. NW1district office
2. NW2Cricklewood
3. NW3Hampstead
4. NW4Hendon
5. NW5Kentish Town
6. NW6Kilburn
7. NW7Mill Hill
8. NW8St John's Wood
9. NW9The Hyde
10. NW10Willesden
11. NW11Golders Green

* added after 1917

Two district offices, then the alphabet

W1 is the Western district office. Paddington, W2, had been a head office of its own since 1878, and the alphabet starts after it: Acton is W3, Chiswick W4, and so on to West Kensington, W14.

The Postmaster-General's own example in June 1917 was a letter for Hyde Park: the number, he said, “conveys the letter to the right delivery office in the Paddington district”.

The alphabet runs twice

Brixton (SW2) to West Brompton (SW10) belonged to the South Western office. Then comes Battersea, SW11, a district office of its own since 1897, and the alphabet begins again: Balham SW12, Barnes SW13, on to Wimbledon, SW19.

That is why Balham and Brixton, 2 km apart, are ten numbers apart.

Twenty-seven offices, and a step of 15 km

The Postmaster-General used the South East to show the problem: 27 delivery offices behind the same two letters.

SE1 is the district office. SE2 is Abbey Wood, 15 km to the east, because A comes first. The alphabet ends at Woolwich, SE18, which borders Abbey Wood.

A second alphabet begins at Norwood, SE19, and runs from Anerley (SE20) to West Norwood (SE27). Norwood had been made a district of its own in 1880. The Post Office's list of districts of 1980 no longer includes it.

Followed in number order, SE1 to SE27 is a journey of 143 km.

Six numbers, and a count that does not add up

The City is EC1 to EC4; WC1 and WC2 lie west of it. The General Post Office signed its own notice from “St. Martin's-le-Grand, E.C. 1”. For these six the booklet prints streets and no office names, so the alphabet cannot be tested on them.

One thing is unexplained. The Postmaster-General counted 112 delivery offices in London, 18 of them in the South West. The booklet uses 116 numbers, 19 of them in the South West.

Four numbers the alphabet never placed

NW11, SW20, SE28 and E20 are not in the 1917 list. Three took the next free number at the end of their district; E20 skipped E19.

NW11, Golders Green. The 1917 list prints its streets under N.W. 4, Hendon, and a history by the Hampstead Garden Suburb residents has their post addressed NW4 until December 1920. By name it would have followed Cricklewood, NW2.

SW20, West Wimbledon and SE28, Thamesmead. Both are in the Post Office's district list of 1980. No source opened for this page gives the year either was created.

E20. Royal Mail created it in March 2011 for the Olympic Park at Stratford. Since 1985 it had been the postcode of Walford, the fictional suburb of EastEnders. The 1917 list stops at E18, and no list seen for this page has an E19.

W1F, EC1A, SW1A: the letter after the number

By July 1968 W1 had full postcodes, and the Post Office planned to finish coding London by 1970. The district of 1917 became the first half of the code.

In W1, WC1, WC2, EC1 to EC4 and SW1 a letter follows the number and divides the district again: W1F, EC1A, SW1A. The letters of W1 in use today date from June 2000, when Royal Mail recoded the district: the old W1M, for one, was divided among W1U, W1G and others. For the other central districts no date was found. E1W, for Wapping, is in postcode data from December 1999, and N1C, for King's Cross, from early 2010.

Where London's letters stop

Greater London was created in 1965. The Post Office left its London district as it was. Asked that April to bring the whole of Barking inside it, the minister answering for the Postmaster-General replied:

“No. Postal and local government areas are not necessarily conterminous…”Joseph Slater, House of Commons, 6 April 1965

So 66,620 of Greater London's 177,264 postcodes, 38 per cent, begin with other letters, most often HA (Harrow), TW (Twickenham), RM (Romford) and UB (Southall and Uxbridge). They are the grey dots on the map.

One piece of London's alphabet lies outside London: 29 postcodes of E4, around Sewardstone, are in Essex.