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

History
There are currently several classes of British national:
British Citizens usually hold this status through a connection with the United Kingdom, Channel Islands and Isle of Man ("United Kingdom and Islands"). Former Citizens of the United Kingdom and Colonies (CUKCs) who possessed right of abode under the Immigration Act 1971 through a connection with the United Kingdom and Islands generally became British citizens on 1 January 1983.
British citizenship is the most common type of British nationality, and the only one that automatically carries a right of abode in the United Kingdom.
BOTC (formerly BDTC) is the form of British nationality held by connection with an existing overseas territory. Nearly all are now also British citizens as a result of the British Overseas Territories Act 2002. It is possible to hold BOTC and British citizenship simultaneously. Unlike BOTCs, all citizens of French overseas dependencies are also French citizens, under the country's nationality law.
BOCs are those former CUKCs who did not qualify for either British citizenship or British Dependent Territories citizenship. Most of these derived their status as CUKCs from former colonies, such as Malaysia and Kenya.
British subjects (as defined in the 1981 Act) are those British subjects who were not CUKCs or citizens of any other Commonwealth country. Most of these derived their status as British subjects from British India or the Republic of Ireland as they existed before 1949.
The status of BNO did not originally exist under the 1981 scheme, but was created by the Hong Kong Act 1985 and the British Nationality (Hong Kong) Order 1986. BNOs are those former Hong Kong BDTCs who applied for the status of BNO prior to the handover of Hong Kong to the People's Republic of China. Hong Kong BDTCs who did not apply to become BNOs, and who did not gain PRC nationality after the handover, became BOCs if they did not have any other nationality.
BPPs derive from those parts of the British Empire which were not officially part of the Crown's dominions, but were instead protectorates or protected states with nominally independent rulers under the "protection" of the British Crown. The status of BPP is sui generis - BPPs are not Commonwealth citizens (British subjects, in the old sense) and were not traditionally considered to be British nationals, but are not aliens either.
Of the various classes of British nationality and BPP status, all except British citizenship and British Overseas Territories citizenship are residual categories. This means that they will become extinct with the passage of time, as they can only be passed down to the national's children 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.

British citizens
British Overseas Territories citizens (formerly British Dependent Territories citizenship) (BOTC)
British Overseas citizens (BOC)
British subjects
British Nationals (Overseas) (BNO)
British protected persons (BPP) Classes of British nationality
British Citizenship can be acquired in the following ways:
For nationality purposes, the Channel Islands and Isle of Man are generally treated as part of the United Kingdom.
Leaflets and advice which give information about how British citizenship and other kinds of British nationality can be held, applied for or renounced are available from the Home Office Immigration and Nationality Directorate. Information is also available on provisions for reducing statelessness.
Persons acquiring citizenship by method (2) are called citizens by descent, while citizens acquiring citizenship by methods (1), (3) or (5) are called 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 automatically; citizens by descent can only pass on citizenship to their non-UK born children by registering them.

lex soli: By birth in the United Kingdom to a parent who is a British citizen at the time of the birth, or to a parent who is settled in the United Kingdom
lex sanguinis: By descent if one of the parents is a British citizen otherwise than by descent (for example by birth, adoption, registration or naturalisation in the United Kingdom). Thus, British actress Emma Watson, born in France to British parents, has British citizenship.
By naturalisation
By registration
By adoption Acquisition of British citizenship
Under the law in effect from 1 January 1983, a child born in the UK to a parent who is a British citizen or 'settled' in the UK is automatically a British citizen by birth
Before 1983, birth in the UK was sufficient in itself to confer British nationality irrespective of the status of parents, with an exception only for 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 (eg US forces stationed in the UK) are British citizens by birth.

only one parent needs to meet this requirement, either the father or the mother.
"settled" status usually means the parent is resident in the United Kingdom and holds Indefinite Leave to Remain (ILR) or Right of Abode. Irish citizens are automatically deemed to hold ILR.
Special rules exist for cases where a parent of a child is a citizen of a European Union or European Economic Area member state, or Switzerland. The law in this respect was changed on 2 October 2000 and again on 30 April 2006. Details
For children born before 1 July 2006, if only the father meets this requirement, the parents must be married. Marriage subsequent to the birth is normally enough to confer British citizenship from that point.
where the father is not married to the mother, the Home Office will usually register the child as British provided an application is made and the child would have been British otherwise. The child must be aged under 18 on the date of application.
where a parent subsequently acquires British citizenship or "settled" status the child can be registered as British provided he or she is still aged under 18.
if the child lives in the UK until age 10 there is a lifetime entitlement to register as a British citizen. The immigration status of the child and his/her parents is irrelevant.
Special provisions may apply for the child to acquire British citizenship if a parent is a British Overseas citizen or British subject, or if the child is stateless. British citizenship by birth in the United Kingdom
Rules for acquiring British citizenship by descent depend on when the person was born.

British Citizenship by descent
A child born outside the UK on or after 1 January 1983 will automatically acquire British citizenship by descent if either parent is a British citizen otherwise than by descent at the time of the birth.

only one parent needs to be British otherwise than by descent - either the father or the mother.
an unmarried father cannot pass on British citizenship automatically in the case of children born before 1 July 2006. Although if the parents marry subsequent to the birth the child normally will become a British citizen at that point if legitimated by the marriage and the father was eligible to pass on British citizenship
failing the above the child can be registered as British if it would have been British if parents were married and application is made before the child is 18.
where the parent is a British citizen by descent additional requirements apply. In the most common scenario, normally the parent is expected to have lived in the UK for three years and apply for the child to be registered as a British citizen within 12 months of the birth.
For British nationality purposes the Isle of Man and Channel Islands are treated as though they were part of the UK.
Before 21 May 2002, British Overseas Territories were treated as 'overseas' for nationality purposes. The exception was the Falkland Islands. For children born on or after 21 May 2002 in a British Overseas Territory (other than the Sovereign Base Areas of Cyprus) there is an entitlement to British citizenship on the same basis as UK born children.
Children born overseas to parents on Crown Service are normally granted British citizenship otherwise than by descent. In other words, their status is the same as it would have been had they been born in the UK.
In exceptional cases, the Home Secretary may register a child of parents who are British by descent as a British citizen under discretionary provisions, for example if the child is stateless. From 1983
Prior to 1983, as a general rule British nationality could only be transmitted from the father through one generation only, and parents were required to be married. See History of British nationality law.
With effect from 30 April 2003, a person born outside the UK to a British mother may be entitled to register as a British citizen by descent if that person was born between 8 February 1961 and 31 December 1982. However those with permanent resident status in the UK, or entitled to Right of Abode, may instead prefer to seek naturalisation as a British citizen which gives transmissible British citizenship otherwise than by descent.

Prior to 1983
A child adopted by a British citizen only acquires British citizenship automatically if:
In both cases, at least one adoptive parent must be a British citizen on the date of the adoption.
In all other cases, an application for registration of the child as a British citizen must be made before the child is age 18. Usually this will be 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.

the adoption order is made by a court in the United Kingdom, Channel Islands, Isle of Man or Falkland Islands on or after 1 January 1983, or in another British Overseas Territory on or after 21 May 2002; or
it is a Convention adoption under the 1993 Hague Convention on Intercountry Adoptions effected on or after 1 June 2003 and the adopters are habitually resident in the United Kingdom on that date. British citizenship by adoption
The requirements for naturalisation as a British citizen depend on whether one is married to a British citizen or not.
For those married to a British citizen the applicant must:
For those not married to a British citizen the requirements are
All applicants for naturalisation must be of "good character". Naturalisation is at the discretion of the relevant authority but is normally granted if the requirements are met.
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 itself) do not have to sit the Life in the UK Test under policies in effect as of August 2006. In due course, it is expected that Regulations will be introduced to that effect in the Channel Islands and Isle of Man. 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 based version of the Life in the UK Test may be available at a British diplomatic mission. Details (pdf)

hold indefinite leave to remain in the UK (or an equivalent such as Right of Abode or Irish citizenship)
have lived legally in the UK for three years
show sufficient knowledge of life in the UK, either by passing the Life in the United Kingdom test or by attending combined English language and citizenship classes. Proof of this must be supplied with one's application for naturalisation. Exemption for this and the language requirement (see below) is normally granted for those aged 65 or over, and may be granted to those aged between 60 and 65.
meet specified English, Welsh or Scottish Gaelic language competence standards. Those who pass the Life in the UK test are deemed to meet English language requirements.
five years legal residence in the UK
indefinite leave to remain or equivalent must have been held for 12 months
the applicant must intend to continue to live in the UK or work overseas for the UK government or a British corporation or association.
the same language and knowledge of life in the UK standards apply as for those married to British citizens Requirements for naturalisation as a British citizen
The immigration status for citizens of European Economic Area states and Switzerland has varied 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. Details (pdf)

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

Prior to 2 October 2000
The Immigration (European Economic Area) Regulations provided that with only a few exceptions, citizens of EU and European Economic Area states are not generally considered to be "settled" in the UK unless they apply for and obtain Indefinite Leave to Remain. 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).

2 October 2000 to 29 April 2006
A further change took place on 30 April 2006 with the coming into force of the Immigration (European Economic Area) Regulations 2006. These provide that citizens of EEA states and Switzerland automatically acquire permanent residence after 5 years resident in the United Kingdom exercising Treaty rights.
Children born in the United Kingdom from this to EEA/Swiss parents will normally be British citizens automatically if at least one parent has been exercising Treaty rights for 5 years. If the parents have lived in the United Kingdom for less than 5 years when the child is born, the child may be registered as British under s1(3) of the British Nationality Act once the parents have completed 5 years residence in the United Kingdom.
Children born between 2 October 2000 and 29 April 2006 may be registered as British citizens as soon as one parent has completed 5 years residence exercising Treaty rights in the United Kingdom.

30 April 2006 onwards
Irish citizens, because of the Common Travel Area provisions between the UK and Republic of Ireland, are exempt from these restrictions and are normally treated as "settled" in the United Kingdom immediately upon taking up residence.

Irish citizens
From 1 June 2002, citizens of Switzerland are accorded EEA rights in the United Kingdom.

Swiss citizens
Greek citizens did not acquire full Treaty rights in the United Kingdom until 1 January 1988 .

Citizens of Greece, Spain and Portugal
Non-British children with an EEA/Swiss parent may be registered as British once the parent becomes "settled" in the United Kingdom under the terms of the Immigration Regulations dealing with EEA citizens.
There is a separate entitlement for any such UK-born child to be registered as British if he or she lives in the United Kingdom until age 10, irrespective of parent's (or child's) immigration status.

Ten year rule
Registration is a simpler method of acquiring citizenship than naturalisation, but only certain people are eligible for it.
British nationals (other than British citizens) who have indefinite leave to remain in the UK or right of abode, are eligible for British citizenship by registration after five years' residence in the United Kingdom. This is an entitlement under s4 of the 1981 Act (section 4 registration).
Other cases where persons may be entitled to registration (either as a matter of law or policy) include:

children born in the UK where a parent obtains British citizenship or indefinite leave to remain after the child is born
children born in the UK who live in the UK until age 10.
children born to a British father who is not married to the mother
British Overseas citizens, British subjects and British protected persons who have no other nationality
certain British nationals from Hong Kong who meet the requirements of the Hong Kong (War Wives and Widows) Act 1996 or the British Nationality (Hong Kong) Act 1997
persons born outside the UK to a British born or naturalised mother between 1961 and 1982
certain children born outside the UK to a British citizen by descent
certain children born in the UK who are stateless
persons who acquire British overseas territories citizenship after 21 May 2002 (except those connected solely with the Sovereign Base Areas of Cyprus)
children under 18 who are adopted outside the United Kingdom by British citizens
former British citizens who renounced British citizenship Registration as a British citizen
The British Nationality Act 1981 contains provisions for acquisition and loss of British Dependent Territories citizenship (BDTC) (renamed as British Overseas Territories citizenship (BOTC) in 2002) on a broadly 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 will a person be registered or naturalised as a BOTC by the Home Office in the United Kingdom.
On 21 May 2002 any BOTC who did not hold British citizenship (except those from the Sovereign Base Areas) automatically acquired it under the British Overseas Territories Act 2002. Those acquring BOTC after that date are entitled to register as British citizens under s4A of the 1981 Act.

Acquisition of British Overseas Territories citizenship
It is currently unusual for a person to be able to acquire British Overseas citizenship, British National (Overseas), British subject or British protected person status. They are not generally transmissible by descent, and nor are they open to acquisition by registration, except for certain instances to prevent statelessness.
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, the then Home Secretary, David Blunkett, said on 3 July 2002 that this would "right a historic wrong" which had left stateless tens of thousands of Asian people who had worked closely with British colonial administrations (see UK to right 'immigration wrong', BBC 5 July 2002).

Persons connected with former British colonies

Main article: British nationality and Hong Kong British National (Overseas) and Hong Kong
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. See also British nationality and the Republic of Ireland

Persons born in the Republic of Ireland
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

Descendants of the Electress Sophia of Hanover

Loss of British nationality
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 that the declaration of renunciation is registered by the Home Secretary. 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 you are considered to have remained a British national.
Renunciations made to other authorities are invalid: e.g., a general renunciation made upon taking up U.S. citizenship.
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 under any circumstances resume their British nationality after renunciation.

Renunciation and resumption of British nationality
British subjects (other than British subjects by virtue of a connection with the Republic of Ireland) and British protected persons will lose their British nationality upon acquiring any other form of nationality, whether British, Commonwealth or foreign.

These provisions do not apply to British citizens.
British Overseas Territories citizens (BOTCs) who acquire another nationality do not lose BOTC status. However they may be liable to lose Belonger status in their home territory under its immigration laws. Such persons are advised to contact the Governor of that territory for information.
British Overseas citizens (BOC) do not lose BOC upon acquisition of another citizenship. However any entitlement to registration as a British citizen on the grounds of having no other nationality will no longer exist after acquiring another citizenship. Automatic loss of British nationality
Under amendments made by the Immigration, Asylum and Nationality Act 2006, British nationals can be deprived of their citizenship if the Secretary of State is satisfied "deprivation is conducive to the public good". 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. This provision only applies to dual nationals — it is not applicable if deprivation would result in a person's statelessness.
Prior to that date, since 2003, under amendments made by the Nationality, Immigration and Asylum Act 2002, British nationals could be deprived of their citizenship if the Secretary of State is satisfied they are responsible for acts seriously prejudicial to the vital interests of the United Kingdom or an Overseas Territory.
British nationals who are naturalised or registered may have their certificates revoked (and hence lose British nationality) if British nationality was obtained by fraud or concealment of a material fact.

Deprivation of British nationality
Since the British Nationality Act of 1948, there is in general no restriction, in United Kingdom law, on a British national being a citizen of another country as well. So, if a British national acquires another nationality, they will not automatically lose British nationality. Similarly, a person does not need to give up any other nationality when they become British.
Different rules apply in the cases of British protected persons and certain British subjects. A person who is a British subject otherwise than by connection with the Republic of Ireland will lose that status on acquiring any other nationality or citizenship. Similarly, a British protected person will no longer be a British protected person on acquiring any other nationality or citizenship. Although British Overseas citizens are not subject to loss of citizenship, a British Overseas citizen may lose an entitlement to register as a British citizen under s4B of the 1981 Act if he acquires any other citizenship.
Many other countries, however, do not allow dual nationality (see Multiple citizenship). If you have British nationality, and are also a national of a country which does not allow dual nationality, the authorities of that country may either regard you as having lost that nationality or may refuse to recognise your British nationality. If you are a British national, and you acquire the nationality of a country which does not allow dual nationality, you may be required by the other country to renounce (give up) your British nationality in order to retain the other citizenship.
Under international law, a State may not give diplomatic protection to one of its nationals in a country whose citizenship that person also holds. For example, if you are British and have another nationality, for example, American, and are visiting the United States, a British Consul in the United States cannot give you diplomatic help.
A British person who acquired foreign citizenship by naturalisation before 1949 may have lost British nationality 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 re-acquired British subject status immediately before the coming into force of the 1948 Act.

Dual nationality and dual citizenship
With effect from 1 January 2004, all new applicants for British citizenship by naturalisation or registration who are aged 18 or over when the application is decided must attend a citizenship ceremony and take an Oath and Pledge to the United Kingdom.
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. However should such a person subsequently apply for British citizenship by registration or naturalisation, attendance at a ceremony will be required.
For those who applied for British citizenship prior to 2004:

local councils in England, Scotland and Wales
the Northern Ireland Office
the governments of the Isle of Man, Jersey and Guernsey
the Governors of British Overseas Territories
British consular offices outside the United Kingdom and Territories.
the oath of allegiance was administered privately through signing a witnessed form in front of a solicitor or other accredited person
those who already held British nationality (other than British protected persons) were exempt, as were those citizens of countries with the Queen as Head of State (such as Australia or Canada). British citizenship ceremonies
British nationals who are "United Kingdom nationals for Community purposes", namely:
are European Union citizens under European Union law.
However, 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. considered "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 with the United Kingdom itself.

British citizens;
British subjects with the right of abode; and
British Overseas Territories citizens connected to Gibraltar Statistics on British Citizenship

United Kingdom passports
British national identity card
Life in the United Kingdom test
Immigration to the United Kingdom
Citizen Information Project
Multiple citizenship
UK topics
Indefinite Leave to Remain
British nationality and the Republic of Ireland
History of British nationality law
British nationality law and Hong Kong