Naturalisation is the process by which an adult foreign national becomes a British citizen. It requires meeting residence, good character, language and knowledge-of-life conditions, after which the Home Office grants citizenship and the person can apply for a British passport.
In one line: Naturalisation is how an adult becomes a British citizen after meeting residence and other Home Office requirements.
How naturalisation works
Applicants usually need to have lived in the UK for a qualifying period, hold indefinite leave to remain or settled status for at least twelve months, meet absence limits, pass the Life in the UK test and satisfy the good character requirement.
For example, a Skilled Worker who obtained ILR in 2025 could apply to naturalise in 2026 once twelve months have passed since settlement and the other conditions are met, paying the application fee and attending a citizenship ceremony if approved.
Successful applicants take an oath or affirmation and pledge at a ceremony, then become British citizens able to hold a UK passport and stand free of immigration control.
Naturalisation vs ILR
ILR is an immigration status that lets a person stay permanently while keeping their original nationality, whereas naturalisation changes nationality by making the person a British citizen.
Naturalisation almost always comes after ILR or settled status, so ILR is the settlement step and naturalisation is the citizenship step that usually follows it.
Primary source: Home Office: Become a British citizen by naturalisation (GOV.UK)