Ive just found another clue, my Robert harper married at tipton church to sarah wilkes 3rd july 1838, sarah wilkes was illigimate daughter born 1820 to Hannah to married joseph Chilton in dec 1820.
The clue is a marriage of a james harper at the same church in tipton same year date 15 October 1838 widower father Thomas harper a miner, to sarah jones widow father Benjamin Dudley, witnesses HANNAH AND JOSEPH CHILTON who are my Robert harpers wife sarahs parents, there must be some link there?
found them on 1851 census james born bilston 1793 coal miner (same as my Robert who was born 1818) he has step children surname jones living with him all in bilston, could Thomas harper the father of Robert and james be the same one, Thomas the father of Robert born near ashby de la zouch who married in 1813 to Catherine gilbert be married previously and living in bilston/darlaston area before remarrying and moving ? could james harper born bilston 1793 be Roberts half brother? any ideas?