Utt, in your case the need for a firearm would be considered the same as a slaughter man. Special dispensation would apply. As an aside, in your case, if you can prove Vetinary use, you could also apply for a Home Office Section 5 certificate. The reason being, dart guns, either rifle, pistol or blow guns, discharge a noxious substance, ie the Immobilon, which is a Section 5 weapon.