British Nationality Act 1981

2 Acquisition by descent

(1) A person born outside the United Kingdom after commencement shall be a British citizen if at the time of the birth his father or mother—

(a) is a British citizen otherwise than by descent; or

(b) is a British citizen and is serving outside the United Kingdom in service to which this paragraph applies, his or her recruitment for that service having taken place in the United Kingdom ; or

(c) is a British citizen and is serving outside the United Kingdom in service under a Community institution, his or her recruitment for that service having taken place in a country which at the time of the recruitment was a member of the Communities.

(2) Paragraph (b) of subsection (1) applies to—

(a) Crown service under the government of the United Kingdom; and

(b) service of any description for the time being designated under subsection (3).

(3) For the purposes of this section the Secretary of State may by order made by statutory instrument designate any description of service which he considers to be closely associated with the activities outside the United Kingdom of Her Majesty's government in the United Kingdom.

(4) Any order made under subsection (3) shall be subject to annulment in pursuance of a resolution of either House of Parliament