List of postcode areas in the United Kingdom

The United Kingdom is divided by Royal Mail into postcode areas. The postcode area is the largest geographical unit used and forms the first characters of the alphanumeric UK postcode.
Subdivision.
Each postcode area is divided into post towns and postcode districts. The London post town is instead divided into several postcode areas.
Scope.
The single or pair of letters chosen for postcode areas are generally a mnemonic for the places served.
Crown dependencies.
The Crown dependencies (which are not part of the United Kingdom) did not introduce postcodes until later, but use a similar coding scheme. They are separate postal authorities.
Defunct postcode areas.
Glasgow.
Glasgow, like London, was divided into compass districts: C, W, NW, N, E, SE, S, SW. When postcodes were introduced, these were mapped into the new "G" postcode: C1 became G1, W1 became G11, N1 became G21, E1 became G31, S1 became G41, SW1 became G51, and so on. As NW and SE had never been subdivided they became G20 and G40 respectively.
Norwich and Croydon.
Norwich and Croydon were used for a postcode experiment in the late 1960s, which was replaced by the current system. The format was of the form NOR or CRO followed by two numbers and a letter, e.g. NOR 07A.
Non-geographic postcodes.
GIR.
GIR 0AA is a postcode created for Girobank in Bootle.
BF.
The BF postcode area was introduced in 2012 to provide optional postcodes for British Forces Post Office addresses, for consistency with the layout of other UK addresses. It uses the national non-geographic post town "BFPO" and, as of 2012, the postcode district "BF1".
BX.
The non-geographic postcode area BX has been introduced for addresses which do not include a locality: this allows large organisations flexibility as to where they receive their mail.
Overseas territories.
Certain British overseas territories have postcodes:
These were introduced to prevent mail being sent to the wrong place, e.g., for St Helena to St Helens, Merseyside and Ascension Island to Asunción, Paraguay, and many on-line companies will not accept addresses lacking a postcode. Such mail is treated as international, not inland, so sufficient postage must be used.