This may be out of date. My elder son was born in Manila in 1995; I was married to someone else and his mother was single; he of course has a Philippines birth certificate and I did not register him at the embassy. I got divorced, two years later I married his mother in Hong Kong and two years after that we moved to the UK. The Liverpool Home Office unit to whom we were referred simply said that since I am British he is British; end of story. He has never had a British birth certificate.
(His current problem is that he wants to drop his Philippines citizenship to join HM Forces.)
