What the author called a 'rumpy' cat is the colloquial term used on the island, along with 'stubbin'. Otherwise the cat is called outside of the island, not surprisingly, a Manx cat. I've seen them scattered around the commonwealth as beloved pets, various tail sizes but probably sadly mutilated for cat shows for a more perfect rump. https://en.m.wikipedia.org/wiki/Manx_cat
tail docking, ear docking, declawing, descenting (of ferrets), is illegal unless for the health of the animal or for a few working breeds where the dog is a working dog.
(England and Wales do have some different laws on this than Scotland and NI)