Master Nationality Rule

The United Kingdom Home Office gave a detailed explanation of the rule:

{{Blockquote|Commonly known as the "Master Nationality Rule", the practical effect of this Article is that where a person is a national of, for example, two States (A and B), and is in the territory of State A, then State B has no right to claim that person as its national or to intervene on that person's behalf. Such a person who goes into the territory of a third state may be treated as a national of either A or B – it does not normally matter which one, except, for example, where the courts of the third state have to adjudicate upon matters relating to that person's status and the relevant laws depend on the person's nationality. In such cases, it is necessary to choose an effective nationality (i.e. one of the two nationalities is selected as effective for the purposes of the third state).{{cite web |url=http://www.ukba.homeoffice.gov.uk/sitecontent/documents/policyandlaw/nationalityinstructions/nisec2gensec/dualnationality?view=Binary |title=Dual Nationality |publisher=UK Home Office |accessdate=16 December 2010 |archiveurl=https://web.archive.org/web/20101208214953/http://www.ukba.homeoffice.gov.uk/sitecontent/documents/policyandlaw/nationalityinstructions/nisec2gensec/dualnationality?view=Binary |archivedate=8 December 2010 }}}}

The United Kingdom Foreign Office restated this in its advice to dual citizens abroad, stating it "would not normally offer you support or get involved in dealings between you and the authorities of that state."{{cite web |url=https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/352141/Support_for_British_Nationals_Abroad_-_a_guide_2_FOI_ref_0606-14.pdf |title=Support for British nationals abroad: A guide |page=5 |publisher=Foreign and Commonwealth Office |year=2011 |access-date=12 February 2024}} The United Kingdom may still make informal diplomatic representations to the authorities of another country when a British citizen is held in another country, even if that person is also a citizen of that country, in case of special humanitarian needs,{{cite web |url=http://www.fco.gov.uk/en/travel-and-living-abroad/when-things-go-wrong/arrest |title=Travel & living abroad: When things go wrong: Arrest or detention |publisher=Foreign and Commonwealth Office |date=8 July 2010 |access-date=7 April 2011 |archive-url=https://web.archive.org/web/20110412150941/http://www.fco.gov.uk/en/travel-and-living-abroad/when-things-go-wrong/arrest |archive-date=12 April 2011}} such as the intervention made by then UK foreign secretary Philip Hammond during the Causeway Bay Books Disappearances.

During the Cold War era, the United States signed consular agreements with certain Warsaw Pact countries providing that a U.S. citizen who entered that country with a U.S. passport and the appropriate visa would not be subsequently treated as a citizen of that country (and hence prevented from leaving).For example see [https://travel.state.gov/law/legal/treaty/treaty_1504.html U.S.-Poland Bilateral Consular Convention] {{Webarchive|url=https://web.archive.org/web/20131106182428/http://travel.state.gov/law/legal/treaty/treaty_1504.html |date=2013-11-06 }}. The Warsaw Pact countries involved (notably Poland) wished to encourage tourism from emigrants and their descendants settled in the U.S. Since the dissolution of the Warsaw Pact in 1991, many of those countries have abolished visa requirements for U.S. citizens thus nullifying those provisions (for detailed discussion see under Dual citizenship in Poland).

Australia,{{cn|date=July 2021}} Canada,{{Cite web | url=http://www.voyage.gc.ca/countries_pays/report_rapport-eng.asp?id=55000#8 |title=China Travel Advice and Advisories |publisher=Foreign Affairs and International Trade Canada |accessdate=April 7, 2011}} and the United States[http://treaties.un.org/doc/Publication/UNTS/Volume%201529/volume-1529-I-26519-English.pdf United States - China Consular convention]. Exchange of Notes I, section 3 (page 18). have concluded similar consular agreements with the People's Republic of China.

In 2006, the International Law Commission adopted draft Articles on Diplomatic Protection, largely codifying established practice, which in general reaffirmed the rule. However it sought to ease the strictness of traditional practice with a proposal that where the nationality of a protecting state is "predominant", diplomatic protection may be given. These draft Articles have not been submitted to a conference to formalize them into a treaty. The draft Article 7 states:{{cite journal |title=Nationality and Diplomatic Protection |year=2018 |publisher=Eileen Denza |doi=10.1007/s40802-018-0119-4 |last1=Denza |first1=Eileen |journal=Netherlands International Law Review |volume=65 |issue=3 |pages=463–480 |s2cid=150320796 |doi-access=free}}

{{Blockquote|A State of nationality may not exercise diplomatic protection in respect of a person against a State of which that person is also a national unless the nationality of the former State is predominant, both at the date of injury and at the date of the official presentation of the claim.{{Cite web|last=International Law Commission|author-link=International Law Commission|date=2006|title=Draft articles on Diplomatic Protection|at=Article 7|url=https://legal.un.org/ilc/texts/instruments/english/draft_articles/9_8_2006.pdf|access-date=13 February 2024}}

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Eileen Denza, Professor of International Law at University College London and a former Legal Adviser in the Foreign and Commonwealth Office, states that the rule is a codification of a "classic rule", and as of 2018, remains "modern state practice" internationally.{{cite web |url=https://www.middleeastmonitor.com/20140419-eileen-denza-expert-on-diplomatic-law-a-response-to-david-pannick-qc/ |title=Eileen Denza, Expert on Diplomatic law: "A response to David Pannick QC" |last=Denza |first=Eileen |website=Middle East Eye |date=19 April 2014 |access-date=19 February 2024}}{{cite web |url=https://referenceworks.brillonline.com/entries/who-s-who-in-public-international-law/denza-professor-eileen-cmg-wwpil_SIM_person_50021 |title=Denza, Professor Eileen, CMG |url-access=subscription |work=Who's Who in Public International Law |publisher=BRILL |access-date=19 February 2024}}

James Larry Taulbee and Gerhard von Glahn, in their 2022 U.S. legal textbook, write that regarding the underlying Articles 3 to 6 of the Convention on Certain Questions Relating to the Conflict of Nationality: "states today in practice follow almost all of those provisions, despite the absence of general conventional rules." They do not use the name "Master Nationality Rule", but explicitly give a summary of the rule.{{cite book |url=https://books.google.com/books?id=JyxsEAAAQBAJ |title=Law among Nations : an Introduction to Public International Law |edition=12th |last1=Taulbee |first1=James Larry |last2=von Glahn |first2=Gerhard |publisher=Routledge |isbn=9781000523584 |chapter=9. Nationality |at=Dual Nationality |year=2022 |access-date=20 February 2024}}

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Category:Multiple citizenship

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