Permanent residency in the UK is also known as the Indefinite Leave to Remain, it is an immigration status granted to a person without the Right of Abode.
A person who has permanent resident status can live and work indefinitely in the UK. He will no longer have immigration restrictions to work or do business in the UK and no time limits on his stay.
You can apply for permanent residency if you have lived in the UK for a certain number of years, lawfully or otherwise.
You have to be in the UK on a work permit for five years before applying for permanent residency.