The CDDO states in its blog post that, administratively, it would be quite simple to retire .GB as it would just be a question of telling the Internet Corporation for Assigned Names and Numbers (ICANN) that .GB is “
no longer needed, and it can thus be removed from the Internet.” However, .GB is a country code Top Level Domain (ccTLD) and all ccTLDs owe their existence to the fact that they are on, or have been added to, the International Organization for Standardization (ISO)’s
ISO 3166 list, the globally authoritative list of two-letter country codes...