British nationality law is the law of the United Kingdom that concerns citizenship and other categories of British nationality. The law is complex due to the United Kingdom's historical status as an imperial power.

English law and Scots law have always distinguished between the Monarch's subjects and aliens, but British nationality law was uncodified until the British Nationality and Status of Aliens Act 1914 codified existing common law and statute, with a few minor changes.

Some thought the single Imperial status of "British subject" was becoming increasingly inadequate to deal with a Commonwealth of independent member states. In 1948, the Commonwealth Heads of Government agreed that each member would adopt a national citizenship (Canada had already done so), but that the existing status of British subject would continue as a common status held by all Commonwealth citizens.

The British Nationality Act 1948 marked the first time that married British women gained independent nationality, regardless of the citizenship of their spouses.^[1] It established the status of Citizen of the United Kingdom and Colonies (CUKC), the national citizenship of the United Kingdom and colonies on 1 January 1949. Until the early 1960s there was little difference, if any, in UK law between the rights of CUKCs and other British subjects, all of whom had the right at any time to enter, live and work in the UK.

Independence acts, passed when the remaining colonies were granted independence, contained nationality provisions. In general, these provisions withdrew CUKC status from anyone who became a citizen of the newly independent country, unless the person had a connection with the UK or a remaining colony (e.g. through birth in the UK). Exceptions were sometimes made in cases where the colonies did not become independent (notable cases include the Crown Colony of Penang and the Crown Colony of Malacca, which were made part of the Federation of Malaya in 1957; CUKC status was not withdrawn from CUKCs from Penang and Malacca even though they automatically acquired Malayan citizenship at the time of independence).

Between 1962 and 1971, as a result of fears about increasing immigration by Commonwealth citizens, the UK gradually tightened controls on immigration by British subjects from other parts of the Commonwealth, which included CUKCs without familial or residential ties to the UK. The Immigration Act 1971 introduced the concept of patriality, by which only British subjects (i.e. CUKCs and Commonwealth citizens) with sufficiently strong links to the British Islands (e.g. being born in the islands or having a parent or a grandparent who was born there) had right of abode, meaning they were exempt from immigration control and had the right to enter, live and work in the islands. The act, therefore, had de facto created two types of CUKCs: those with right of abode in the UK, and those without right of abode in the UK (who might or might not have right of abode in a Crown colony or another country). Despite differences in immigration status being created, there was no de jure difference between the two in a nationality context, as the 1948 Act still specified one tier of citizenship throughout the UK and its colonies. This changed in 1983, when the 1948 Act was replaced by a multi-tier nationality system.

The current principal British nationality law in force, since 1 January 1983, is the British Nationality Act 1981, which established the system of multiple categories of British nationality. To date, six tiers were created: British citizens, British Overseas Territories citizens, British Overseas citizens, British Nationals (Overseas), British subjects, and British protected persons. Only British citizens and certain Commonwealth citizens have the automatic right of abode in the UK, with the latter holding residual rights they had prior to 1983.

Aside from different categories of a nationality, the 1981 Act also ceased to recognise Commonwealth citizens as British subjects. There remain only two categories of people who are still British subjects: those (formerly known as British subjects without citizenship) who acquired British nationality through a connection with former British India, and those connected with the Republic of Ireland before 1949 who have made a declaration to retain British nationality. British subjects connected with former British India lose British nationality if they acquire another citizenship.

In spite of the fact that the 1981 Act repealed most of the provisions of the 1948 Act and the nationality clauses in subsequent independence acts, the acquisition of new categories of British nationality created by the 1981 Act was often dependent on nationality status prior to 1 January 1983 (the date the 1981 Act entered into force), so many of the provisions of the 1948 Act and subsequent independence acts are still relevant. Not taking this into account might lead to the erroneous conclusion, for example, that the 1981 Act's repeal of the nationality clauses in the Kenya Independence Act of 1963 restored British nationality to those who lost their CUKC status as a result of Kenya's independence in 1963. This is one of the reasons for the complexity of British nationality law; in complicated cases, determining British nationality status requires an examination of several nationality acts in their original form.

As of August 2019, there are six classes of British nationality.^[2]

The following two classes of British nationality are "active", meaning that they can be acquired by any eligible person at birth or by naturalisation or registration.

The four residual categories are expected to lapse with the passage of time. They can be passed to children only in exceptional circumstances, e.g., if the child would otherwise be stateless. There is consequently little provision for the acquisition of these classes of nationality by people who do not already have them. To reduce de facto statelessness, most are allowed to be registered as British citizens as long as they hold no other citizenship or nationality.

Only the status of British citizen carries with it the right of abode in a certain country or territory (in this case, the UK).

In practice, BOTCs (except those associated with the Sovereign bases in Cyprus) were granted full British citizenship in 2002; BN(O)s have right of abode or right to land in Hong Kong (note: not conferred by the status itself, but by the Immigration Ordinance of Hong Kong) and are eligible for registration as British citizens if they hold no other nationality under the Borders, Citizenship and Immigration Act 2009; BSs and BPPs lose their statuses upon acquiring another nationality (except BSs connected with the Republic of Ireland) and so should be eligible for registration as British citizens under the Nationality, Immigration and Asylum Act 2002.

British Overseas citizens are unique in that their nationality status is not associated with a right of residence, and only certain types of BOCs are eligible to be registered as British citizens under the Nationality, Immigration and Asylum Act 2002.

British Citizenship can be acquired in the following ways:

For nationality purposes, the Channel Islands and the Isle of Man are generally treated as if they were part of the UK.^[4]

Information about British citizenship and other kinds of British nationality is available from Her Majesty's Government.^[5] Information is also available on provisions for reducing statelessness.^[6]

Persons acquiring citizenship by method (2) are called British citizens by descent; those acquiring citizenship by methods (1), (3) or (5) are called British citizens otherwise than by descent. British citizens by registration, method (4), may be either, depending on the circumstances. Only citizens otherwise than by descent can pass on their citizenship to their children born outside the UK or a British Overseas Territory automatically; British citizens by descent can pass on citizenship to their non-UK born children only by meeting certain UK residence requirements and registering them before the age of 18.

From 1 January 1983, a child born in the UK or the Falkland Islands^[7] to a parent who is a British citizen or "settled" in the UK or the Falkland Islands is automatically a British citizen by birth. This provision is extended to children born to such parents in any remaining British Overseas Territory other than Akrotiri and Dhekelia after 21 May 2002. Since 13 January 2010, a child born to a parent who is a member of the British Armed Forces at the time of birth also automatically acquires British citizenship if he or she was born in the UK or a qualified British Overseas Territory.

Even if a child is born in the UK on or after 1 January 1983 but does not acquire British citizenship at birth, the child is considered a lawful resident in the UK and is not required to apply for leave to remain.^[13][14] The child, however, is subject to immigration control and the child's parent(s) can choose to apply to regularise the child's immigration status through the granting of leave to remain (for the same period as that held by the parent(s)). If the child leaves the UK, he/she must hold leave to enter or remain in order to return to the UK.^[15]

Between 1949 and 1982, birth in the UK or a Crown Colony was sufficient in itself to confer the status of Citizen of United Kingdom and Colonies (CUKC), irrespective of the parents' status, although only CUKCs with a connection to the UK (i.e. birth in the UK or has a UK-born parent or grandparent) had right of abode in the UK after 1971 and would eventually become British citizens in 1983. CUKCs without a connection to the UK became either British Overseas Territories citizens or British Overseas citizens in 1983, depending on whether they had a connection to another BOT.

The only exception to this rule were children of diplomats and enemy aliens. This exception did not apply to most visiting forces, so, in general, children born in the UK before 1983 to visiting military personnel (e.g. US forces stationed in the UK) were CUKCs connected to the UK and would become British citizens in 1983, albeit as a second nationality.

"British citizenship by descent" is the category for children born outside the UK or an Overseas Territory to a British citizen. Rules for acquiring British citizenship by descent depend on when the person was born.

A child born outside the UK, Gibraltar or the Falkland Islands on or after 1 January 1983 (or outside another British Overseas Territory on or after 21 May 2002) automatically acquires British citizenship by descent if either parent is a British citizenotherwise than by descent at the time of the child's birth.

Before 1983, as a general rule CUKC status was transmitted automatically only for one generation, with registration in infancy possible for subsequent generations. Transmission was from the father only, and only if the parents were married. (See History of British nationality law.)

In 1979 the Home Office had begun to take quiet steps to address this gender discrimination by allowing British citizen mothers to register children born abroad at the local British consulate within one year of birth, just as British citizen fathers could.^[19][20] However, the change was without great publicity and was largely unnoticed, and in 2002, Parliament formalized the approach in law, by enacting amendments to the British Nationality Act 1981 allowing children who had been covered by the 1979 procedural change (because they were under 18 years old at that time) to register themselves at any point later in life.^[19][20] The class of eligible registrants was later expanded in 2009, and was upheld by a 2018 UK Supreme Court ruling.^[19][20]

Several laws also accorded a right of registration to children born of unmarried British citizen fathers.

Children born outside the UK before 1 January 1983 to a CUKC mother who became a British citizen on 1 January 1983 and a foreign father are not British citizens by birth, and neither are children born between 1 January 1983 to 1 July 2006 to a British citizen father and a foreign mother out of wedlock.

In the face of various concerns over gender equality, human rights, and treaty obligations, Parliament moved to act on these situations.^[20]

The Nationality, Immigration and Asylum Act 2002 inserted a section 4C into the British Nationality Act 1981 allowing for registration as a British citizen of any person born between 7 February 1961 and 1 January 1983 who would have become a CUKC if the British Nationality Act 1948 had provided for mothers to transmit citizenship in the same way that fathers could.^[21] The Borders, Citizenship and Immigration Act 2009 then expanded the earliest date of birth covered from 1961 to 1 January 1949, and elaborated in "a dense and at times impenetrable piece of drafting"^[22][20] on the section's approach, while also covering numerous additional and less common situations, and adding a good character requirement.^[23]

Registration through this method is performed with Form UKM. After approval, the registrant must attend a citizenship ceremony. Since 2010, there is no longer an application fee (of £540). Applicants do however still have to pay £80 for the citizenship ceremony.^[24]

From 6 April 2015, a child born out of wedlock before 1 July 2006 to a British father is entitled to register as a British citizen by descent under the Immigration Act 2014 using form UKF.^[25] Such child must also meet character requirements, pay relevant processing fees and attend a citizenship ceremony.^[26] However, if the applicant has a claim to register as a British citizen under other clauses of the British Nationality Act 1981, or has already acquired British citizenship after being legitimised, the application will be refused.

Alternatively, if already resident in the UK, these children may seek naturalisation as a British citizen, which gives transmissible British citizenship otherwise than by descent.

Under section 5 of the Ireland Act 1949, a person who was born in the territory of the future Republic of Ireland as a British subject, but who did not receive Irish citizenship under the Ireland Act's interpretation of either the 1922 Irish constitution or the 1935 Irish Nationality and Citizenship Act (because he or she was no longer domiciled in the Republic on the day the constitution came into force and was not permanently resident there on the day of the 1935 law's enactment and was not otherwise registered as an Irish citizen) was deemed to be a Citizen of the United Kingdom and Colonies.^[27][28]

As such, many of those individuals and some of the descendants in the Irish diaspora of an Irish person who left Ireland before 1922 (and who was also not resident in 1935) may both be registrable for Irish citizenship and be a British citizen,^[29] through either:

In some cases, British citizenship may be available to these descendants in the Irish diaspora when Irish citizenship registration is not, as in instances of failure of past generations to timely register in a local Irish consulate's Foreign Births Register before the 1986 changes to Irish nationality law and before births of later generations.^[29]

A child adopted by a British citizen acquires British citizenship automatically only if:

In both cases, at least one adoptive parent must be a British citizen on the date of the adoption.

The requirements are different for persons adopted before 1983.

In all other cases, an application for registration of the child as a British citizen must be made before the child is 18. Usually this is granted provided the Secretary of State accepts the adoption is bona fide and the child would have been a British citizen if the natural child of the adopters. Usually the adoption must have taken place under the law of a 'designated country' (most developed nations along with some others are 'designated' for this purpose) and be recognised in the UK. This is the standard method for children adopted by British citizens permanently resident overseas to acquire British citizenship.

The cancellation or annulment of an adoption order does not cause loss of British citizenship acquired by that adoption.

British children adopted by non-British nationals do not lose British nationality, even if they acquire a foreign nationality as a result of the adoption.

Any person who obtains British nationality by this method is British otherwise than by descent, which means they have the same status as those born or naturalised in the UK and can pass on British nationality to their children.

Naturalisation as a British citizen is at the discretion of the Home Secretary, who may grant British citizenship to anyone they "think fit".^[32] Although the Home Office sets down official requirements for naturalisation they may waive any of them, or may refuse citizenship to a person even if they meet all of the requirements.^[33] However, applications for naturalisation are normally granted if the requirements are met.

The requirements for naturalisation as a British citizen depend on whether or not one is the spouse or civil partner of a British citizen.

For those married to or in a civil partnership with a British citizen, the applicant must:

For those not married to or in a civil partnership with a British citizen, the requirements are:^[38][39]

Those applying for British citizenship in the Channel Islands and Isle of Man (where the application is mainly based on residence in the Crown Dependencies rather than the UK) do not have to sit the Life in the UK Test. In the Isle of Man, there is a Life in the Isle of Man Test, consisting of certain questions taken from the Life in the UK Test syllabus and certain questions taken from a separate syllabus relating to matters specific to the Isle of Man. In due course it is expected that Regulations will be introduced to that effect in the Channel Islands. The provisions for proving knowledge of English, Welsh or Scottish Gaelic remain unchanged until that date for applicants in the Crown Dependencies. In the rare cases where an applicant is able to apply for naturalisation from outside the United Kingdom, a paper version of the Life in the UK Test may be available at a British diplomatic mission.^[40]

As of 11 February 2009, wait times for naturalisation applications were reportedly up to 6 months.^[41] The UK Border Agency stated that this was occurring because of the widespread changes proposed to the immigration laws expected to take effect in late 2009.^[42]

Fees for naturalisation (including Citizenship ceremony fee) have been rising steadily faster than inflation;

The immigration status for citizens of European Economic Area states and Switzerland has changed since 1983. This is important in terms of eligibility for naturalisation, and whether the UK-born child of such a person is a British citizen.^{[[43]](https://portal.issn.org/resource/ISSN/"European Economic Area and Swiss nationals")}

In general, before 2 October 2000, any EEA citizen exercising Treaty rights in the United Kingdom was deemed "settled" in the United Kingdom. Hence a child born to that person in the United Kingdom would normally be a British citizen by birth.

The Immigration (European Economic Area) Regulations^[44] provided that with only a few exceptions, citizens of EU and European Economic Area states were not generally considered "settled" in the UK unless they applied for and obtained permanent residency. This is relevant in terms of eligibility to apply for naturalisation or obtaining British citizenship for UK born children (born on or after 2 October 2000).

On 30 April 2006, the Immigration (European Economic Area) Regulations 2006 ^[101] came into force, with citizens of EEA states and Switzerland automatically acquiring permanent residence after 5 years' residence in the UK exercising Treaty rights.

Children born in the UK to EEA/Swiss parents are normally British citizens automatically if at least one parent has been exercising Treaty rights for five years. If the parents have lived in the UK for less than five years when the child is born, the child may be registered as British under section 1(3) of the British Nationality Act once the parents complete five years' residence.

Children born between 2 October 2000 and 29 April 2006 may be registered as British citizens as soon as one parent has completed five years' residence exercising Treaty rights in the UK.

Because of section 2(1) of the Ireland Act 1949 (which states that the Republic of Ireland would not be treated as a foreign country for the purposes of British law), Irish citizens are exempt from these restrictions and are normally treated as "settled" in the UK immediately upon taking up residence. This status will not be changed by Brexit confirmed by the British government in March 2019

From 1 June 2002, citizens of Switzerland are accorded EEA rights in the UK.

Greek citizens did not acquire full Treaty rights in the UK until 1 January 1988^[45] and citizens of Spain and Portugal did not acquire these rights until 1 January 1992.^[45]

Non-British children with an EEA or Swiss parent may be registered as British once the parent becomes "settled" in the UK under the terms of the Immigration Regulations dealing with EEA citizens.

A separate entitlement exists for any such UK-born child registered as British if they live in the UK until age 10, regardless of their or their parent's immigration status.

Registration is a simpler method of acquiring citizenship than naturalisation, but only certain people holding a form of British nationality or having a connection to the UK are eligible. In general, language proficiency and knowledge requirements do not apply to applicants for registration.^[46]

BOTCs who acquired their citizenship after 21 May 2002 (except for those connected solely with the Akrotiri and Dhekelia) may request registration under section 4A of the 1981 Act without further conditions other than the good character requirement. Registration under section 4A grants citizenship otherwise than by descent.^[47] Those connected with Gibraltar may also elect to apply for registration under section 5 of the 1981 Act which grants citizenship by descent.^[47]

British nationals who are not British citizens (other than BOTCs solely connected with Akrotiri and Dhekelia) have an entitlement for registration as British citizens under s4 of the 1981 Act provided the following requirements are met:

This confers citizenship otherwise than by descent.^[47]

However, BOTCs solely connected with Akrotiri and Dhekelia are not eligible for registration and must apply for naturalization instead. Naturalization also grants citizenship otherwise than by descent.

Other cases where British nationals who are eligible to register without residency requirements are:

Other cases where non-British nationals may be entitled to registration (either as a matter of law or policy) include:

The Home Secretary can exercise discretion under section 3(1) of the 1981 Act and register any child as a British citizen even if they may not meet the formal criteria.^[63] Certain adopted children would also be registered under this provision if their adoptions were not made in accordance with the Hague Convention.^[64] Registration under section 3(1) confers citizenship otherwise than by descent if neither parent was a British citizen at the time of registration, or by descent if either parent was a British citizen at that time.^[47]

The British Nationality Act 1981 contains provisions for acquisition and loss of British Dependent Territories citizenship (BDTC) (renamed British Overseas Territories citizenship (BOTC) in 2002) on a similar basis to those for British citizenship. The Home Secretary has delegated his powers to grant BOTC to the Governors of the Overseas Territories. Only in exceptional cases is a person naturalised as a BOTC by the Home Office in the UK.

It is unusual for a person to be able to acquire British Overseas citizenship, British subject or British protected person status. They are not generally transmissible by descent, nor are they open to acquisition by registration, except for certain instances to prevent statelessness. It is also not possible for any person to acquire British National (Overseas) status as the registration period for such status had permanently ended on 31 December 1997.

The Nationality, Immigration and Asylum Act 2002 granted British Overseas Citizens, British Subjects and British Protected Persons the right to register as British citizens if they have no other citizenship or nationality and have not after 4 July 2002 renounced, voluntarily relinquished or lost through action or inaction any citizenship or nationality. Previously such persons would have not had the right of abode in any country, and would have thus been de facto stateless. Despite strong resistance from senior officials at the Home Office,^[65] the then Home Secretary, David Blunkett, said on 3 July 2002 that this would "right a historic wrong" that left stateless tens of thousands of Asian people who had worked closely with British colonial administrations.^[66] This provision was extended to British Nationals (Overseas) in 2009.

British Overseas citizenship is generally held by persons connected with former British colonies and who did not lose their British Nationality upon the independence of those colonies.

After the withdrawal of BDTC status from all BDTCs by virtue of a connection with Hong Kong on 30 June 1997, most of them are now either British Nationals (Overseas) and/or British citizens (with or without nationality of China), or Chinese nationals only. The remaining few became British Overseas citizens.

Before the handover in 1997, former BDTCs from Hong Kong had been able to acquire British citizenship under legislation passed in 1990, 1996 and 1997. In other cases, certain persons may already hold British citizenship as a matter of entitlement or through registration under normal procedures.

Although it is no longer possible to acquire British National (Overseas) status after 31 December 1997, stateless children born to such parents are entitled to British Overseas citizenship and can subsequently apply to register as British citizens under the Nationality, Immigration and Asylum Act 2002. Since 2009, BN(O)s without other nationalities or citizenship are able to register as British citizens under the Borders, Citizenship and Immigration Act 2009 as well.

British citizens and BN(O)s who are of full or partial Chinese descent are also Chinese nationals under Chinese law unless they have renounced their Chinese nationality with the Hong Kong SAR Government. As China does not recognise multiple nationality, those persons are considered by China as solely Chinese nationals before and after the handover of Hong Kong and hence are not eligible for consular protection when on Chinese soil. Although holding the same nationality under the Chinese nationality law, Chinese nationals with a connection to Hong Kong or Macau have been categorised differently from Chinese nationals domiciled in Mainland China.

In February 2006, in response to extensive representations made by Lord Avebury and Tameem Ebrahim,^[67] British authorities announced that 600 British citizenship applications of ethnic minority children of Indian descent from Hong Kong were wrongly refused.^[68] The applications dated from the period July 1997 onwards. Where applicants in such cases confirm that they still wish to receive British citizenship, the decision is reconsidered on request. No additional fee is required in such cases. A template to request reconsideration is available for those who want a prior application reconsidered.^[69]

Approximately 800,000 persons born before 1949 and connected with the Republic of Ireland remain entitled to claim British subject status under section 31 of the 1981 Act.

Eligible descendants from the Electress Sophia of Hanover may hold British Overseas citizenship based on their status as British subjects before 1949. Where such a person acquired a right of abode in the UK before 1983, it is possible for British citizenship to have been acquired. See also History of British nationality law and Sophia Naturalization Act 1705.

All categories of British nationality can be renounced by a declaration made to the Home Secretary. A person ceases to be a British national on the date the Home Secretary registers the declaration of renunciation. If a declaration is registered in the expectation of acquiring another citizenship but one is not acquired within six months of the registration, it does not take effect and the person remains a British national.

Renunciations made to other authorities (such as the general renunciation made as part of the US naturalisation ceremony) are not recognised by the UK. The forms must be sent through the UK Border Agency's citizenship renunciation process.^[70] There are provisions for the resumption of British citizenship or British overseas territories citizenship renounced for the purpose of gaining or retaining another citizenship. This can generally only be done once as a matter of entitlement. Further opportunities to resume British citizenship are discretionary.

British subjects, British Overseas citizens and British Nationals (Overseas) cannot resume their British nationality after renunciation.

British subjects (other than British subjects by virtue of a connection with the Republic of Ireland) and British protected persons lose British nationality upon acquiring any other form of nationality.

After the Nationality, Immigration and Asylum Act 2002 came into force British nationals could be deprived of their citizenship if and only if the Secretary of State was satisfied they were responsible for acts seriously prejudicial to the vital interests of the United Kingdom or an Overseas Territory.

This was extended under the Immigration, Asylum and Nationality Act 2006; people with dual nationality who are British nationals can be deprived of their British citizenship if the Secretary of State is satisfied that "deprivation is conducive to the public good",^[71] or if nationality was obtained by means of fraud, false representation or concealment of a material fact.^[72] There is a right of appeal. This provision has been in force since 16 June 2006 when the Immigration, Nationality and Asylum Act 2006 (Commencement No 1) Order 2006 came into force.^[73] Loss of British nationality in this way applies also to dual nationals who are British by birth.^[71][74] The Secretary of State may not deprive a person of British nationality, unless obtained by means of fraud, false representation or concealment of a material fact, if they are satisfied that the order would make a person stateless. This provision was modified by the Immigration Act 2014 so as not to require that a third country would actually grant nationality to a person; British nationality can be revoked if "the Secretary of State has reasonable grounds for believing that the person is able, under the law of a country or territory outside the United Kingdom, to become a national of such a country or territory."^[75] The powers to strip citizenship were initially very rarely used. Between 2010 and 2015, 33 dual nationals had been deprived of their British citizenship.^[76] In the two years to 2013 six people were deprived of citizenship; then in 2013, 18 people were deprived, increasing to 23 in 2014. In 2017, over 40 people had been deprived as of July (at this time increased numbers of British citizens went to join "Islamic State" and then tried to return).^[77]

The Home Office does not issue information on these cases and is resistant to answering questions,^[71] for example under the Freedom of Information Act 2000.^[78] It appears that the government usually waits until the person has left Britain, then sends a warning notice to their British home and signs a deprivation order a day or two later.^[71] Appeals are heard at the highly secretive Special Immigration Appeals Commission (SIAC), where the government can submit evidence that cannot be seen or challenged by the appellant.^[71]

Home Secretary Sajid Javid said in 2018 that until then deprivation of nationality had been restricted to "terrorists who are a threat to the country", but that he intended to extend it to "those who are convicted of the most grave criminal offences". The acting director of Liberty responded “The home secretary is taking us down a very dangerous road. ... making our criminals someone else’s problem is ... the government washing its hands of its responsibilities ... Banishment belongs in the dark ages."^[76]

As of August 2018, there is no restriction in UK law on a British national holding in addition citizenship of other countries; indeed the Good Friday Agreement explicitly recognises the right of qualified residents of Northern Ireland to be British, Irish, or both.

Different rules apply to British protected persons and certain British subjects (that do not apply to British citizens). A person who is a British subject other than by connection with the Republic of Ireland loses that status on acquiring any other nationality or citizenship,^[79] and a British protected person ceases to be such on acquiring any other nationality or citizenship. Although British Overseas citizens are not subject to loss of citizenship, British Overseas citizens may lose an entitlement to register as a British citizen under s4B of the 1981 Act if they acquire any other citizenship.

A number of other countries do not allow multiple citizenship. If a person has British nationality and is also a national of a country that does not allow dual nationality, the authorities of that country may regard the person as having lost that nationality or may refuse to recognise the British nationality. British nationals who acquire the nationality of a country that does not allow dual nationality may be required by the other country to renounce British nationality to retain the other citizenship. None of this affects a person's national status under UK law.

Under the international Master Nationality Rule a state may not give diplomatic protection to one of its nationals with dual nationality in a country where the person also holds citizenship.

A British subject who acquired foreign citizenship by naturalisation before 1949 were deemed to have lost his or her British subject status at the time. No specific provisions were made in the 1948 legislation for such former British subjects to acquire or otherwise resume British nationality, and hence such a person would not be a British citizen today. However, women who lost British nationality on marriage to a foreign man before 1949 were deemed to have reacquired British subject status immediately before the coming into force of the 1948 act.

The UK is a signatory to the Convention on the Reduction of Cases of Multiple Nationality and on Military Obligations in Cases of Multiple Nationality (1963 Strasbourg Convention). Chapter 1 requires that persons naturalised by another European member country automatically forfeit their original nationality^[80] but the UK ratified only Chapter 2, so the convention does not limit the ability of British citizens to become dual citizens of other European countries.^[81]

From 1 January 2004, all new applicants for British citizenship by naturalisation or registration aged 18 or over if their application is successful must attend a citizenship ceremony and either make an affirmation or take an oath of allegiance to the monarch, and make a pledge to the UK.

Citizenship ceremonies are normally organised by:

Persons from the Republic of Ireland born before 1949 reclaiming British subject status under section 31 of the 1981 Act do not need to attend a citizenship ceremony. If such a person subsequently applies for British citizenship by registration or naturalisation, attendance at a ceremony is required.

For those who applied for British citizenship before 2004:

British nationals who are "United Kingdom nationals for European Union purposes", namely:

have become citizens of the European Union under European Union law and enjoy rights of free movement and the right to vote in elections for the European Parliament.^[82] When in a non-EU country where there is no British embassy, British citizens have the right to get consular protection from the embassy of any other EU country present in that country.^[83][84] British citizens can live and work in any country within the EU as a result of the right of free movement and residence granted in Article 21 of the EU Treaty.^[85]

By virtue of a special provision in the UK Accession Treaty, British citizens who are connected with the Channel Islands and Isle of Man (i.e. "Channel Islanders and Manxmen") do not have the right to live in other European Union countries (except the Republic of Ireland through the long-established Common Travel Area) unless they have connections through descent or residence in the United Kingdom.

The Home Office Research and Statistics Division publishes an annual report with statistics on grants of British citizenship broken down by type and former nationality. Since 2003, the report has also included research on take-up rates for British citizenship.

Visa requirements for British citizens are administrative entry restrictions by the authorities of other states placed on citizens of the United Kingdom. In 2017, British citizens had visa-free or visa on arrival access to 173 countries and territories, ranking the British passport 4th in terms of travel freedom (tied with the Austrian, Belgian, Dutch, French, Luxembourgish, Norwegian and Singaporean passports) according to the Henley visa restrictions index.^[86] Additionally, the World Tourism Organization also published a report on 15 January 2016 ranking the British passport 1st in the world (tied with Denmark, Finland, Germany, Italy, Luxembourg and Singapore) in terms of travel freedom, with a mobility index of 160 (out of 215 with no visa weighted by 1, visa on arrival weighted by 0.7, eVisa by 0.5, and traditional visa weighted by 0).^[87]

Visa requirements for other classes of British nationals such as British Nationals (Overseas), British Overseas Citizens, British Overseas Territories Citizens, British Protected Persons or British Subjects are different.

The British nationality is ranked thirteenth in Nationality Index (QNI). This index differs from the Visa Restrictions Index, which focuses on external factors including travel freedom. The QNI considers, in addition, to travel freedom on internal factors such as peace & stability, economic strength, and human development as well. ^[88]