You may need proof of paternity from the other parent before you give their details if they aren’t going to the registry office with you.
If you don't have any of these, the registrar can still register a child's birth. Afterwards, you’ll be provided with a certificate summarising the birth entry, free of charge. However, a full birth certificate can be obtained from the registrar for a fee.
To find your local register office use the finder at the Direct.gov website».