I'm not sure of your source of information. I have researched the popkiss line along with other and have not found any high office associated so early with the Popkiss Line. Athelstan Popkess was Chief Constable of Nottinghamshire but in the 1930s.
The founder of the Popkiss line in England was a Dutch sailor called Peter Popkes -this became alliterated into Popkiss in 18th cenury England.
The name was vowel shifted nearer the original as members of the family emigrated to the various overseas colonies of the British Empire and to the U.S.A.
The family line can be found at
Please do not hesitate to contact me if you need more information