Many people are automatically British nationals. They may not know it or they may be unsure. But they are.
There are different sorts of British nationals: British citizens, British overseas territories citizens, British Overseas citizens, British Subjects, British Protected Persons, and British Nationals (Overseas). The most numerous are British citizens, who comprise most of the inhabitants of the United Kingdom and the British overseas territories. Many British citizens are also to be found in other countries around the world.
Those British citizens born in the UK itself or in the British overseas territories will have a British citizen parent or a parent who is settled in that place (e.g. a person with indefinite leave to remain in the UK). In order to be settled, the parent will need to be ordinarily resident in the UK (so not visiting) and present without being subject any time restriction on their permission to be there. There are also people who become British citizens automatically by virtue being adopted in the UK or a Hague Convention country, or where a parental order is made.
Where born in a foreign country, a British citizen by descent will have a British citizen parent. The British Nationality Act 1981 sets out when a person is a British citizen by descent or otherwise than by descent. That classification affects a person’s ability to transmit British citizenship to the next generation.
There are also people who became British citizens on 1 January 1983 when the British Nationality Act 1981 came into force, having been Citizens of the United Kingdom and Colonies with a right of abode in the UK immediately prior to that date. In a similar way, there are people from the British overseas territories who were made British citizens by a provision of the British Overseas Territories Act 2002.
All these people with have automatically acquired British citizenship without a grant of citizenship or naturalisation.
People who are automatically British nationals include British overseas territories citizens (BOTCs); they have a connection to a remaining British overseas territory such as the Cayman Islands or the Falkland Islands.
British citizens and BOTCs have connections to the UK or a remaining British overseas territory.
In addition, there are many people around the world who are British nationals of one sort or another today because of ties to the UK and former British possessions (e.g. a Colony) that date back to the colonial era.
There are people who are British Overseas citizens (BOCs), who have no connection to the UK or to a remaining British overseas territory, but who have a connection to a former British Colony (or even a Protected State, protectorate, League of Nations Mandate, or United Nations Trust Territory) that dates from the colonial era. Usually, these are people who were alive during the colonial era or their children or grandchildren.
Then there are British Protected Persons (BPPs), again a class of people whose connection to former British possession dates back to the colonial, this time to Protected States, protectorates, League of Nations Mandates, or United Nations Trust Territories. Usually, these are people who were alive during the colonial era or their children or grandchildren.
In addition, there are also British Subjects, some of whom were born in pre-1949 Ireland/Eire, but many of whom are from India or Pakistan. In respect of the latter they are people who did not pick up their citizenships of India or Pakistan when those countries enacted their nationality laws after independence and who therefore retained their British Subject status.
There are also people from Hong Kong, who are British Nationals (Overseas), under legislation enacted as part of the process of returning Hong Kong to Chinese rule. That status had to be applied for and thus was not automatically acquired by operation of law.
Finally, there are people who have acquired a form of British nationality (as a British citizen, BOTC, etc.) under the British Nationality Act 1981 because they were born Stateless and would otherwise remain so but for the conferral of British nationality. Indeed, it is possible for a person to be born today and to acquire automatically one of these forms of British nationality because they would otherwise be Stateless.
All such persons are British nationals.
Some Common Cases
British citizenship of course is largely acquired by birth in the UK or a British overseas territory (but not the British sovereign base areas in Cyprus) to a qualifying parent (a British citizen or person otherwise settled) or by descent where born outside the United Kingdom and the British overseas territories (but not the British sovereign bases in Cyprus) to a British citizen parent.
British overseas territories citizenship works in a similar way to British citizenship for those whose connection is solely to a British overseas territory. The British overseas territories include a number of populated islands in the Caribbean such as the Cayman Islands, the Turks & Caicos Islands, British Virgin Islands, and so on, as well as sparsely populated places like the Falkland Islands and Pitcairn Island, and even uninhabited territories such as British Antarctic Territory.
There are many people today who are British Overseas citizens (BOCs) by virtue of a connection to a former colonial possession. Such persons may or may not have picked up the nationality of a newly independent Commonwealth country during the era of decolonisation. There are a number of common fact patterns that give rise to BOC status today.
For example, there are many people of Lebanese descent, whose family members may have been commercial traders or merchants in what was formerly British West Africa, and who did not acquire any the nationality of a newly independent country. Thus, there are a number of BOCs of Lebanese heritage. Their connection is to one of the former British possessions in West Africa, to one of the places that are now the independent countries of Gambia, Sierra Leone, Ghana, and Nigeria.
There are also BOCs of Somali heritage who were born in Aden (now in Yemen) during the colonial era, who did not pick up the nationality of South Yemen (now Yemen) under the provisions made for its independence.
Other examples abound. There are people of Chinese heritage who lived in Penang and Malacca (now part of Malaysia) during the colonial era who remain British nationals (and who today are BOCs) under special arrangements made during the era of de-colonisation, notwithstanding the fact that they picked up Malayan citizenship/Malaysian citizenship on independence.
There are also British Protected Persons (BPPs) who can trace family connections back to a former British Protected State, protectorate, League of Nationals Mandate, United Nations Trust Territory, or Colony. Commonly in Africa such persons are found in what are now the independent countries of Kenya, Uganda, Zambia, or Malawi. BPPs may also be found elsewhere, for example in former British West African states now Gambia, Sierra Leone, Ghana and Nigeria, as well as in Brunei in South East Asia, and in former protectorates in southern Africa.
There are many other examples of British nationals with an historic connection to Britain in the colonial era. There are so many possibilities is is impossible to list them all. Where there is a doubt, it is always worth checking.