Do I qualify for British Citizenship?

[tyronvt]

Instead of paying £250 for a trace I was hoping somebody could please shed some light on my situation. My father, who resides in South Africa, was adopted by a British Citizen in 1957 in Rhodesia. I have all the legal documents for this. He received a British passport at the time but it has since expired. I am now living in the UK and would like to apply for a British passport on the basis that my father is a British Citizen but I'm unsure whether this applies to me. Is my father considered a British citizen even if he no longer holds a passport and has never resided in the UK and if so on what basis can I apply for citizenship?