I was born in South Africa and was registered in Cape Town, with my parents getting a copy of the South African Birth Certificate. Dad was in the Royal Navy at the time, serving at Simonstown Naval Base. I was also registered at the British Consular Office in Cape Town and entered into my mother's passport as a British Citizen. Twenty years later in 1967 I applied for a British Passport but was told that there was no record of my birth in the British Consular Records and I could not have a British passport as I was a South African citizen. [I was presumably also an illegal immigrant, having entered UK in 1950 on a false passport
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I eventually claimed British Citizenship By Descent by proving from my documents that I was the legitimate child of parents who were British by birth and that my father was the legitimate child of a father who was a British citizen by birth. The citizenship law has, since then, become even stricter.
Our youngest was born in Brunei in December 1982 and under the new citizenship law that came into force at midnight on 31st, she would not have acquired British citizenship either by birth or by descent. She made it by just two weeks! As my wife is Malaysian and I am not British by birth, this could have repercussions on our children, should they move abroad to work and have children born abroad. So far all our grandchildren have been born in UK.