Hi Again,
I've just made another connection which leads me to believe that the family I found in the 1851 census is very likely to be your William's:
1861 Census, Walcott, Bath
Ref: RG9/1693 Folio 32 Page 22
Address: 9 Chappel Row
William FORSE, Lodger, Mar, 37, Fly? Proprietor, b. Clifton, Gloucestershire
Elizabeth ditto, Wife, Mar, 35, Chiropodist, b. Bath, Somerset
William ditto, Son, 10, Scholar, b. Kingston, Surrey
I think it would be worth asking for a baptism lookup on the Gloucestershire board for William Senior before trying the GFHS.
Regards,
Al