History
By the 1850s, the rapid growth of the metropolitan area meant it became too large to efficiently operate as a single post town.

Origins
The NE and S divisions were abolished following a report by Anthony Trollope. In 1866 NE was merged into the E district and in 1868 the S district was split between SE and SW.

NE and S
In 1917, as a wartime measure to improve efficiency, the districts were further subdivided with a number applied to each sub-district.
The boundaries of each sub-district rarely correspond to any units of civil administration such as parishes or boroughs; despite this they have developed over time into a primary reference frame. The numbered sub-districts were later used as the outward code (first half) of the postcode system implemented during the 1970s.
There have been a number of ad-hoc changes to the organisation of the districts, such as the creation of SE28 from part of SE2 because of the construction of the high density Thamesmead development.

Numbered divisions
The initial system was designed at a time when the official London boundary was restricted to the square mile of the small, ancient City of London. The area it covered ('the metropolis') consisted of parts of the counties of Middlesex, Surrey, Kent, Essex and Hertfordshire. In 1889 a County of London was created which was somewhat smaller than the postal district. Around 40 of the sub-districts created in 1917 were outside its boundary with Leyton in Essex, Ealing in Middlesex, Totteridge in Hertfordshire and Wimbledon in Surrey served by the London postal area but outside the County of London.
In 1965 the creation of Greater London caused London's boundary to expand to include these places officially as well as postally, however the new boundary went far beyond these postal districts. Royal Mail were unable to follow this change and expand the postal district to match because of the prohibitive cost. Places in London's outer boroughs such as Harrow, Enfield, Ilford, Romford, Bromley, Richmond and Croydon are therefore covered by parts of twelve adjoining postcode areas (EN, IG, RM, DA, BR, TN, CR, SM, KT, TW, HA and UB). Royal Mail now has a policy of only changing postcodes if there is an operational advantage to them and has no plan to change the postcode system to match up with the Greater London boundaries.
The London postal district currently includes all of the City of London and the City of Westminster, all of the boroughs of Camden, Hackney, Hammersmith and Fulham, Haringey, Islington, Kensington and Chelsea, Lambeth, Southwark, Tower Hamlets and Wandsworth; very nearly all of Greenwich, Lewisham, Newham and Waltham Forest; parts of Barnet, Bexley, Brent, Bromley, Croydon, Ealing, Enfield, Harrow, Hounslow, Kingston, Merton, Redbridge and Richmond. Barking and Dagenham, Havering, Hillingdon and Sutton are entirely outside the postal district. Sewardstone in the Epping Forest district of Essex is anomalously the only place to be outside the Greater London boundary but within the London postal district.

Relationship to London boundary
It is common to use postal districts as placenames in London, particularly in the property market: a property may be described as being "in N11", especially where a postal district is synonymous with a desirable location but also covers other less prestigious places. They are a convenient shorthand for social status, such that a 'desirable' postcode may add significantly to the value of property, and property developers have pressed for the boundaries of postal districts to be altered so that new developments will sound as though they are in a richer area. Some groups on the fringes of the London postal districts lobby to be excluded or included in an attempt to decrease their insurance premiums (see SE2) or raise the prestige of their business (see IG1). This is generally futile as the Royal Mail only changes postcodes in order to facilitate the delivery of post.

Significance

All Head District Sorting Offices, except London South East, were connected by and had stations on the Post Office Underground Railway.
The BBC soap opera EastEnders is set in the fictional postal district of E20.
The pop group East 17 took their name from the postcode for Walthamstow. Trivia
All London postal districts were traditionally prefixed with the post town 'LONDON' and full stops were commonly placed after each figure.
e.g. LONDON S.W.1.
Use of the full stops ended with the implementation of the national postcode system. More recently, the Royal Mail have specified that the post town and district should each appear on a separate line in order to increase the effectiveness of their OCR equipment.

Presentation
See the postcode area articles for a full list of the places the districts cover.

List of London postal districts


Outer districts

List of postal codes in the United Kingdom