just to update this thread. I purchased the birth certificate that seemed the likely match....(William Thomas Roberts
June q, 1877, St Asaph, 11b 392)
but it was not my William.
I also purchased the marriage cert (Sept q, 1875, St Asaph, 11b 500 with Daniel Roberts and Anne Williams) This seems likely to be my Great Grandparents.
The GRO have carried out two searches on my behalf to find a record of William Thomas Roberts between 1870 and 1880 but they were unable to find one whose parents were Daniel and Anne.
Do you think its worth another shot to ask them to search for his birth just using his mothers name? If he was illegitimate will it say so?