[1] The codes and structures for the United Kingdom (UK) are provided to the ISO in Geneva by the British Standards (BS) and the Office for National Statistics (ONS).
Currently for the United Kingdom of Great Britain and Northern Ireland, ISO 3166-2 codes are defined for the following primary divisions and subdivisions: Each ISO 3166-2:GB code consists of two parts; both parts are in upper-case capital letters, and are separated by a hyphen (without spaces).
The first part for the is GB, the ISO 3166-1 alpha-2 code of the United Kingdom of Great Britain and Northern Ireland.
The second part is three letters, which is the British Standard BS 6879 three-letter code of the individual subdivision.
[3] The codes GB-EAW, GB-GBN, and GB-UKM are only mentioned in remark part 2 in the ISO website, where they are 'included for completeness'.