I used to hunt squirrels with a Crosman 2100 flinging Copperhead pellets at 725 fps. My uncle used to kill feral cats with a Crosman 760 flinging BBs. I killed a large, vicious chow mix that made the mistake of growling and baring it's teeth, with it's ears laid back while approaching me in my own yard.
Seems the Brits do a fair bit of bunnywhacking with 12 ft lb air rifles.