Hi Paul, The 1911 census shows him living in Swinton, Rotherham. The GRO shows a birth in 1905 Rotherham mother Dove. There is a marriage for William Case to Jane Dove 1890 in Clay Cross, Chesterfield. Regards Barry
I may have a lead for you -a Frederick Case is on the 1939 census he gives a birth date of12 Dec 1904. He seems to die in 1941. Looking at the electoral registers him and Phyllis live Wath Road, Mexborough - just up the street is William and Margaret Case. In 1911 Frederick is living Wath Road with father William(widower)and several siblings.
In 1939 there is a Frederick Case in Crookill Hall Receiving House Conisbrough Doncaster could this be the same Frederick.
The GRO shows Fredericks mothers maiden name as Dove - so lots to check out.