If you have settled status (i.e. have Indefinite Leave to Remain - ILR or, in the case of European (EU) nationals, permanent residence) in the UK then you can stay here without any time limit, whatever your nationality. You do not have to become a British Citizen. However, this is something many people who have made the UK their permanent home do wish to consider.
Other people may wish to know whether they are, or can become, a British Citizen because of their family or personal history.
There are three main ways to become a citizen, be born one, be registered as one, and be naturalized as one.
Registration is the only way in which children can become British (may also be used for adults in special circumstances). It is necessary for those over ten years old to be of good character, but it is not necessary to demonstrate knowledge of the language or of life in the UK.
Naturalisation is the most common way for adults who were not born British to become British. People who have Indefinite Leave to Remain (ILR) can, subject to fulfilling residence requirements, apply to naturalise as British Citizens. It is necessary to demonstrate that you are aged 18 or over and are not of unsound mind, you meet either the three or five years residence rule, sufficient knowledge of the language, and of life in the UK, and to be good character. Taking a test or undertaking a course of study can do this. Naturalisation takes place at a public ceremony.