- the United Kingdom of Great Britain and Northern Ireland (formerly the United Kingdom of Great Britain and Ireland);
- the Bailiwick of Guernsey (including the jurisdictions of Alderney, Guernsey and Sark); and
- the Bailiwick of Jersey;
- the Isle of Man.
The Isle of Man and the Bailiwicks of Guernsey and Jersey are Crown dependencies and are not a part of the United Kingdom. The Parliament of the United Kingdom on occasions introduces legislation that is extended to the islands, normally by the use of Orders in Council. For this reason it has been found useful to have a collective term for the combined territories. Dating back to 1889, a statutory definition can be found in the Interpretation Act 1978.
British passports issued in the UK have the wording "United Kingdom of Great Britain and Northern Ireland" on their cover. In the Crown dependencies, this is replaced by "British Islands – Bailiwick of Jersey", "British Islands – Bailiwick of Guernsey" or "British Islands – Isle of Man". These passports are issued to all British citizens resident in the jurisdiction in question.
Section 5 of the Interpretation Act 1978 provides that "in any Act, unless the contrary intention appears" the expression "British Islands" is to be construed according to Schedule 1 of that Act, which contains the following paragraph:
"British Islands" means the United Kingdom, the Channel Islands and the Isle of Man.
Subject to paragraph 4(2) of Schedule 2, that paragraph of Schedule 1 applies, so far as applicable, to Acts passed after the year 1889.
Paragraph 4(2) provides:
Irish Free State
The Irish Free State was established on 6 December 1922 and the Interpretation Act 1978 came into force on 1 January 1979.
The Interpretation Act 1978 applies to itself and to any Act passed after the commencement of that Act and, to the extent specified in Part I of Schedule 2, to Acts passed before the commencement of that Act.
- Text of the Interpretation Act 1978 as in force today (including any amendments) within the United Kingdom, from legislation.gov.uk.
- "Interpretation Act 1978" (PDF). Margaret Marks legal translations. Archived from the original (PDF) on 27 September 2007. Retrieved 28 October 2007.
-  Archived 21 August 2008 at the Wayback Machine
- "britishcitizen.info" (PDF). britishcitizen.info. Archived from the original (PDF) on 1 September 2009. Retrieved 3 September 2013.
- "Immigration Act 1971". Legislation.gov.uk. Retrieved 3 September 2013.
- "States of Guernsey passports". Guernsey Government Website. Archived from the original on 20 November 2008. Retrieved 6 February 2009.
- The Interpretation Act 1978, Schedule 2, paragraph 4(1)
- The Interpretation Act 1978, section 22(1)