Indefinite Leave to Remain
Once permanent residence (properly known as indefinite leave to remain) has been granted, there are no longer any immigration related restrictions on the work or business you may do in the UK, and no time limits on your stay in the UK.

In order to keep your permanent residence you should not spend longer than two years outside the UK. You should also maintain ties to the UK and you must consider the UK as your home. If you continue to only spend short periods of time in the UK over many years it is likely that there will come a time when you will lose your indefinite leave to remain in the UK.  You can normally apply for naturalisation as a UK citizen one year after being granted indefinite leave to remain and as long as you meet the residence requirements.

Permanent residence Time needed to gain permanent residency:

HSMP and work permit = 5 years
Ancestry = 5 years
Marriage = 2 years
Unmarried partners = 2 years
Investors = 5 years
Unlawful stay or a combination of lawful and unlawful stay = 14 years
Lawful stay on any basis = 10 years