What are the requirements for registering a child who was born outside of the UK to a parent who is British by descent? 

A child who is born to parents that have British Citizenship outside of the UK should be eligible to be registered as a British Citizen providing the parents have lived in the UK continuously for 3 years prior to their birth. During the 3-year period the parents have lived in the UK, they must not have been outside of the country for more than 270 days in total. There may also be an option to register if the child and relevant parent live in the UK for a 3-year period after the child’s birth, but before they turn 18.