The British government is quite strict and demands the aptitude of your documentation when you apply for UK citizenship.
Seeking UK citizenship could be one option wherein if you are born before January 1983 you are a British citizen and if born on or after the year 1983 you need either of your parents to be a British citizen. You can also apply through naturalisation if you already have one citizenship and want UK citizenship as well through dual nationality process. Another way is by being a refugee and applying for British citizenship. Basic requirements needed are life in the UK test, age above 18 years, a good character and English proficiency.
Read more - Is it easy to get citizenship in the UK?