Finally tracked down the marriage certificate of an elusive ancestor. He was married in 1871 in Scotland but has put unknown for both parents.
I can't find a birth certificate for him anywhere in the UK. Surely you would have a birth certificate even if you didn't know who your parents were? Would he be in an orphanage or something? Or would his birth just not be registered?
We've been researching our family tree a lot recently and usually everything is quite boring and straight forward. This is the most curious person I've found so far.