Hi there....I'm not sure if your Ggrandfather is related as the Edwin (Hobbs?-)Chapman in my family tree was born in Stanford Dingley in Berkshire. Here is the info from the 1851 census:
Stanford Dingley Dist 6
HO107/1691 FOLIO 146 PAGE 3
Joseph HOBBS, Head, 31, Journeyman Tanner
Hannah HOBBS, Wife, 41, , b Pewsey Wilts
Henry HOBBS, Son, 4
Charles HOBBS, Son, 2
Ann HOBBS, Daur, 11m
Thomas CHAPMAN, Stepson, 15, Blacksmith
Marth CHAPMAN, Stepdaur, 12
Albert CHAPMAN, Stepson, 10
Edwin CHAPMAN, Stepson, 8
This would make Edwin Chapman's birth year as 1843 and his father was George Chapman. George Chapman died and then Hannah his wife remarried, Joseph Hobbs. They went on to have 3 children together. There is a small chance that Edwin took the Hobbs with Chapman as his own since he is the youngest of the Chapman children however I haven't researched him in later census records to confirm this.
I would suggest you obtain a copy of your Ggrandad's birth certificate as this will confirm the facts either way.
Good luck, regards
Katie