Someone who has been legally resident in the UK for five years (or in the case of the wife or husband of a British citizen, three years) can apply for naturalisation as a British citizen:
The applicant's stay must not be subject to any time limit on the date of application; the applicant must be 18 or over and not of unsound mind, but does not have to meet the requirements to have sufficient knowledge of the language and to intend to live in the United Kingdom once naturalised. He or she must be of good character, however.
To meet the residence requirements, you must not have been absent from the United Kingdom for more than 450 days over the 5 year period, or for more than 270 days over the 3 year period. In each case, you must not be absent for more than 90 days in the last year of the period.
More information and application forms for British citizenship can be obtained from the Home Office's British Citizenship website.
http://www.uknationality.gov.uk/content ... epage.html
