Hi again Alison,
Although this doesn't help you find John's parents, its worth having the full set of census entries.
In 1861 he was living at Stratisfieldsaye, Hampshire:
John Fenn Head marr 39 groom Coggeshall Essex
Jane Fenn Wife marr 34 Gosport Hampshire
John Fenn son unm 11 Pimlico Middlesex
Joseph Fenn son unm 2? " "
RG9 710 67 18
In 1871 at Old Dairy House, Stratisfield, Hampshire
John Fenn Head 49 groom Coggershill Essex
Jane Fenn Wife 45 Gosport Hants
Elizabeth Fenn dau 9 Stratisfield Hampshire
RG10 1236 79 31
Amanda
