A foreign national prisoner is any prisoner who is not a British Citizen. The law which governs who is British is complicated so if a person is unsure whether or not they are a British Citizen they may require specialist legal advice.
British Citizenship extends to citizens of British Overseas Territories which are: Anguilla Bermuda British Antarctic Territory British Indian Ocean Territory British Virgin Islands Cayman Islands Falkland Islands Gibraltar Montserrat Pitcairn Islands St Helena and Dependencies South Georgia and the South Sandwich Islands Turks and Caicos