British citizenship referee is a vital part of the British naturalisation application. People who will stand as your referees have to be those that have known you for a period of three years at least. One among them can come from any nationality but must have a professional standing like police, accountant, chemist, etc.
Normally, the second person must be of British nationality and must have a British citizen passport. He may or may not be a professional person but his age must be above 25 years.