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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.[1]
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.
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.
These were introduced to prevent mail being sent to the wrong place, e.g., for St Helena to St Helens, Merseyside[9] 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.
