This is only my opinion, but based on my experiences. When the plummers were first around, they were bred to hopefully be digging dogs. Hence the shape/size they were. When the hunting ban came in certain breeders (not all) have changed the look of the terrier, after first promoting the dog as an earth dog they changed tact as they believed at first digging was banned, then realised that the general public would find the thought of a dog killing fox less appealing than a dog killing horrible nasty vermin, so the current plummers you see are skinny long legged, now promoted as ratting dogs...wh