The following is applicable when claiming British citizenship through a British naturalised father.
The applicant, the child of the naturalised father, must have been born after the father’s naturalisation. If born before the father’s naturalisation then the applicant/child is not eligible for a British passport.
Applicants born before 1 July 2006
British law requires that an applicant’s birth needs to be registered with the British authorities before applying for a first-time passport, if the applicant’s parents were never married to each other, at any point, before or after the applicant’s birth.
If the applicant’s parents were married to each other at any point, before or after the applicant’s birth, then a birth registration is not applicable and the applicant can apply for a British passport without a birth registration.
Applicants born after 1 July 2006
Birth registrations are not applicable if the applicant was born outside the United Kingdom after 1 July 2006. Therefore, the applicant is eligible for a British passport without registering his/her birth.