I guess the recent past immigration concerns have caused significant tightening up.
My wife was born in 1950 in Sri Lanka, of ex-military father who chose to be demobbed and continued to work out there; both he and his wife were born in India, although all 4 grandparents were born in Ireland near Cork. Her birth certificate was needed some years later after they returned to UK, and a duplicate supplied by their Embassy, in very colourful Sinhalese with several official stamps (but no English translation.)
Fast forward to 1979, when my job took me to South Africa for a one week trip which turned into nearly 3 months. The company offered for her to join me for the rest of my trip, which left her with the problem of getting a passport (previously we had only visited Europe using the Post Office counter pink travel cards, cheaper and simpler). Advised by a friend to apply at the Petty France Passport office ("they will see you are white") she arrived there with application form, photographs and 5 year old son in tow, and was interviewed. Officer went over available papers, and then asked if she had her parents marriage certificate. When she explained that during a heated argument with her father her mother had thrown it in the fire, poor chap visibly wilted, replied 'I suppose I can assume as they had 9 children, then they were married' and asked her to wait outside. 30 minutes later she was summoned and handed a shiny new passport, which has been renewed without question several times since, and used to travel extensively, including USA.
I don't know what would happen if she tried that today.