This page explains how a child born outside the United Kingdom who has lived here for the last three years with his or her parents can be registered as a British citizen.
A child will have an entitlement to be registered under section 3(5) of the British Nationality Act 1981 if:
If the parents' marriage or civil partnership has ended or they are legally separated, only the child and one parent need to satisfy the residence requirement.
A child registered under this section will become a British citizen otherwise than by descent and will be able to pass British citizenship on automatically to any of their children born outside the United Kingdom.
Living apart from a husband, wife or civil partner without divorcing or legally ending the partnership. No formal legal document is necessary to prove legal separation provided the couple are not living together. A couple can be separated but still live under the same roof if they arrange the household so that they no longer sleep or eat together, and do not do domestic chores, such as washing or ironing, for each other.