Do I have British citizenship by descent?

[Youngpretender]

Do I qualify as a British citizen, and therefore qualify for a passport? I will be claiming from my father

Here are the details:
Father - born in 1948 in tanganyika
He moved to London in 1969.
He has a British passport from 1978 that lists him as a “British subject Citizen of the United Kingdom and Colonies”. Under observation it lists “the holder has the right to abode in the United Kingdom.
His 1988 passport lists him as a “British Citizen” and holds a valid British passport til this day.

I was born in the US in 1996, my parents were married before I was born.

I am basing my theory on the fact that he gained British citizenship automatically based on his continuing residence from 1969 until the the BNA of 1981 came into effect causing him to transition into a British citizen automatically. He didn’t naturalise or register.

As he got British citizenship in his own right, and not by descent. It means I am eligible. Basically, my father became a British citizen otherwise than by descent under:
• Section 11(1)(a) of the British Nationality Act 1981, as he was a CUKC with the right of abode in the UK.
• His right of abode arose from Section 2(1)(c) of the Immigration Act 1971, based on his residence in the UK

Is this sound reasoning?

[contorted_svy]

I think you are correct. An easy way to check for this is to submit a passport application with marriage certificate, your birth certificate, your dad's birth certificate and relevant passports, a cover note stating all the above, and see what they say.