British Citizenship by Registration
This route is for those qualified either by way of an entitlement or on a discretionary basis to apply for British Citizenship by registration. In order to be eligible to register as a British Citizen, the applicant may qualify in a number of permitted categories, the most common route being children under the age of 18 applying for registration.Children cannot apply to ‘naturalise’, but instead must apply to ‘register’ as British citizens.
British Citizenship by registration for children
The Home Office may also register a child under discretion and grant British citizenship. The applications are decided on individual merits and normally consider the child’s future intentions, the citizenship and immigration status of the child’s parents,the length of the child’s residence in the UK, whether or not the child is settled,parental consent and what is in the child’s best interests. The good character requirement applies on both types of registration and a high threshold applies on the discretionary registrations.
The child would need to make an application under MN1 form for registration and pay the required fees & complete the process.