The goofiness of gun laws in general can be illustrated by the change in attitudes towards the Greener Killer, on both sides of "The Pond." Until about 1986, these devices were NOT regarded as "firearms" in the UK, and no license was needed to possess one at all. Following the Hungerford and Dunblane shooting incidents, the Greener Killers and their ammunition were re-classified, and the same stringent laws that covered other handguns were applied to it. This is the case today, and though it's unlikely a licensed veterinarian would have any problem getting a Possession and Acquisition License, the associated "safe storage" and transport regulations are so onerous few will bother doing so, as the captive bolt killers are license free.
In the USA the exact reverse has happened. From 1934 to 1986, the Greener Killer was regarded as an "Any Other Weapon" under the National Firearms Act, treated in the same way as machine guns and sawed-off shotguns, requiring a special Treasury Department license to buy, and dire consequences for someone in possession of an "unregistered" Killer. In 1986, with the passage of the Firearm Owners' Protection Act, someone at the BATF had a fit of sanity and the Killers were de-listed as "AOW" firearms. They're no longer under the NFA and you can own one (if you can find one!) without hassle.
I have a colleague who emigrated from the UK many years ago, who brought with him a Pocket Model Killer which had been issued to his father in law, who'd been a Veterinary Surgeon in the Royal Horse Artillery in the 1930's. Had my friend's bags been thoroughly inspected on entry into the USA he might just about now be getting out of prison.