Hi Emma,
I can't add anything to your search for Benjamin, but I have an interest in his son John. John married into the Pinckard family and after a spell in the marines they moved to Poplar in the East End. In the 1861 census the Pinckard's are using the name Westbury and Sometime after 1862 and before 1871 John adopted the name Dunkley, which you found out was his mothers maiden name. After Johns' death his family reverted to Hillary. My interest is with his friend and work colleague William Thomas Crawford, my ancestor. William also married into the Pinckard family and also used an alias Cummin/g/s but he retained the name even for a subsequent marriage. (My family still continues to use the name today).
Bit of a long shot but has your bosses family have any idea why John adopted an alias?
David