British nationality law is notoriously complex and is unfortunately also known for being discriminatory on the grounds of sex.
Historically, British nationality could only be passed on by the father. This discrimination was (partially) rectified from 1 January 1983, when it became possible for mothers to pass on British nationality to their children.
In 2003 the law was changed retrospectively, to allow those born before 1983 to also acquire British citizenship through the female line.
Children born outside the UK to British parents acquire British nationality by descent, but they cannot pass that nationality on to their own children, unless they register the child with the local consulate within one year of birth.
Ms Romein’s mother was a British national, born in South Africa. Following the 2003 rule change, Ms Romein applied for British nationality, but her application was rejected, because she had not been registered with the local consulate within one year of her birth. This requirement was impossible for her to comply with, as at the time she was born, it was only possible to register children with British fathers, not British mothers.
Considering her case, the Supreme Court held that the requirement to register should simply be disapplied in circumstances where nationality was derived from the applicant’s mother. This common sense approach is welcome and should help to remove some of the persistent sex discrimination in the British nationality rules.
The Advocate General for Scotland v Romein (Scotland)  UKSC 6