Great grid. I did not get the Sumner group but, in an odd twist all of the answers in that group are streets in Swindon, three of them within about half a mile of each other. All of them are Victorian streets so can't have anything to do with the real, less parochial, answer.

thanks for setting. if there were red herrings here I was too dumb to see them, not knowing the Curtis group, though one could reasonably solve the grid just by guessing what was a surname