Qualify for British citizenship?

Hi
I am completely stumped so hope someone has some guidance!
My brother-in-law is South African citizen born in 1986 and would like to apply for a British passport. His father is a British Citizen (as per his passport), born in Harare in 1960.
Would anyone know where I can find info or whether he would have to apply for citizenship or apply directly for a British passport?
I have been on the gov.uk website and am more confused than when I started
Any advice will be appreciated.
Thanks

1. You should ask your friend to register on the forum and ask their questions and this is not as simple as a 'yes or no' situation.

2. The first question we will ask is where were the grandparents born, what year was everyone father backwards born etc. etc. etc.

Thank you for the quick reply. I will get him to register