The system of London postal districts in the inner part of London predated the introduction of postcodes throughout the United Kingdom in the 1960s. The first system, of ten sectors identified by letters, was introduced in 1858; the numbered subdivisions date from 1917. The 1917 subdivisions remain important, because they form the first part of the two-part modern postcode (so N1 1AA is an address in the old N1 district), and because they continue to be used by Londoners to refer to their districts.
The London postal districts are organized by sectors, as follows, and then numbered within their sectors.
- In central London, WC and EC (West Central and East Central)
- In the outer part of inner London, N, NW, SW, SE, W and E.
- In outer London the disticts derive from the location of the main sorting office, as with other UK postcodes.
Matters are confused further by the fact that the postal districts considered to be "London" do not correspond to local government boundaries - neither the pre-1965 London County Council nor the Greater London Council/Greater London Authority boundaries are identical to the area covered by EC, EW, N, NW, E, W, SE & SW. As a result there are places within Greater London that don't have "London" postcodes (eg, Enfield).
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".
The postal districts are:
- EC1, EC2, EC3, EC4
- WC1, WC2
- N1, N2, N3, N4, N5, N6, N7, N8, N9, N10, N11, N12, N13, N14, N15, N16, N17, N18, N19, N20, N21, N22
- NW1, NW2, NW3, NW4, NW5, NW6, NW7, NW8, NW9, NW10, NW11
- E1, E2, E3, E4, E5, E6, E7, E8, E9, E10, E11, E12, E13, E14, E15, E16, E17, E18
- W1, W2, W3, W4, W5, W6, W7, W8, W9, W10, W11, W12, W13, W14
- SE1, SE2, SE3, SE4, SE5, SE6, SE7, SE8, SE9, SE10, SE11, SE12, SE13, SE14, SE15, SE16, SE17, SE18, SE19, SE20, SE21, SE22, SE23, SE24, SE25, SE26, SE27, SE28
- SW1, SW2, SW3, SW4, SW5, SW6, SW7, SW8, SW9, SW10, SW11, SW12, SW13, SW14, SW15, SW16, SW17, SW18, SW19, SW20
There are no London postal districts labelled "NE" or "S". These were in the initial division but were later removed as they were considered unnecessary. These two codes have since been applied to Newcastle Upon Tyne and Sheffield respectively.
The outer London postal districts do not fully comply with the boundaries of Greater London. The following include areas approximately within the boundary of the M25 motorway:
- AL2
- BR1, BR2, BR3, BR4, BR5, BR6, BR7, BR8
- CM14, CM16
- CR0, CR2, CR3, CR4, CR5, CR6, CR7, CR8
- DA1, DA2, DA4, DA5, DA6, DA7, DA8, DA14, DA15, DA16, DA17, DA18,
- EN1, EN2, EN3, EN4, EN5, EN6, EN7, EN8, EN9
- HA0, HA1, HA2, HA3, HA4, HA5, HA6, HA7, HA8, HA9
- IG5, IG6, IG7, IG8, IG9, IG10, IG11
- KT1, KT2, KT3, KT4, KT5, KT6, KT7, KT8, KT9, KT10, KT11, KT12, KT13, KT17, KT18, KT19, KT20, KT21, KT22,
- RM1, RM2, RM3, RM4, RM5, RM6, RM7, RM8, RM9, RM10, RM11, RM12, RM13, RM14, RM15
- SL0
- SM1, SM2, SM3, SM4, SM5, SM6, SM7
- TN14, TN15, TN16
- TW1, TW2, TW3, TW4, TW5, TW6, TW7, TW8, TW9, TW10, TW11, TW12, TW13, TW14, TW15, TW16, TW17, TW19
- UB1, UB2, UB3, UB4, UB5, UB6, UB7, UB8, UB10, UB11
- WD1, WD2, WD3, WD4, WD5, WD6, WD7