Who can register a birth
If the parents of the child are married, either the mother or the father can provide the information to the Registrar who will register the birth.
If the parents are not married:-
the mother can provide the information to the Registrar even when she is under 16 or
the father can provide the information but only if he has the agreement of the mother. She must give this agreement by signing a declaration (Form DPM) and the father must sign a declaration (Form 27). From 4 May 2006, if an unmarried father jointly registers the birth of his child with the child's mother he will automatically acquire parental responsibilities and rights towards the child
As I thought, he can't just go and do it by himself.