I have similar issues. My birth certificate is in my first surname, my marriage certificate is in another name, marrying to a third name.. I've nothing that links my birth certificate to my "unmarried" family name except for a single line that has been struck through in my very first UK passport that states simply "child also known as *****". Luckily I never threw that first passport away because without it I would not have got an Australian passport.
Because of that we know I can not under any circumstances allow either passport to expire. Renewing is much easier than applying for a new one and if I lose that original UK passport, I can't prove my names at all. (There was no legal requirement in the UK for my name to be changed to that of my mother's 2nd husband. It was changed by common usage, nothing more otherwise he would have had to legally adopt us which would have meant losing child support payments from my real father). My brother was able to return to his birth name without too many issues, but both of us have issues proving our academic history because those certificates are all in the 2nd unadopted name.