You must meet certain requirements before applying for British citizenship by descent. You must be a British overseas citizen, British national, British protected person or British subject under the 1981 Nationality Act. You must not be a citizen of another country or have given up or lost citizenship in another country. British citizenship gained by descent cannot be passed on to children who are born outside of the United Kingdom.
Get the B(OS) Application for British Citizenship by Descent. This application is available for download at the UK Border Agency website. An application is provided below under Resources.
Fill out Sections 1, 2 and 4 of the application. Section 1 asks for your personal information and information regarding your parents, such as their names and where they were born. Section 2 asks for your nationality information. Section 4 is where you will sign the application attesting to the truthfulness of the information you have provided elsewhere in the application. Be sure to print in black ink.
Affix your passport-size photo in the box on Section 3 of your application.
Get two referees (references), who have known you for at least three years, to fill out Section 3 of your application. One referee must be a working professional of any nationality--for example, a teacher or member of the clergy. The second referee must have a British passport and be either a working professional or over the age of 25. The referees cannot be related to you or to each other. The referees will certify in Section 3 that they know you and that they know of no reason why you should be denied British citizenship. Your referees may be contacted by authorities to verify their identity and to confirm that they are eligible to act as referees.
Get evidence of British nationality. You will need your British passport or naturalisation certificate if you are a British overseas citizen, British protected person, British national or British subject.
Get evidence that you do not hold citizenship in another country. Get a letter from authorities in the country where you were born stating that you do not hold their citizenship. If you submit your application without this documentary evidence, it may be denied.
Mail your application. You will need to include your British passport or naturalisation certificate, letter stating you do not hold another country's citizenship, and a check for £550 payable to the UK Border Agency. Your current location determines where your application should be sent. You will find the addresses on the UK Border Agency website. There is also a link listed below under Resources. Your application will be processed within six months and you will be notified to attend a citizenship ceremony.
Attend the ceremony. You will affirm your allegiance to the Queen and to the UK. You will be given a certificate of registration and officially become a British citizen.