The most humane and rapid way to dispatch a mink is to shoot it through the head. Death is immediate and painless. WRT recommends the use of a .22 air rifle. Those under the Firearm Certificate power threshold can be freely bought, held and used in England and Wales with no license, but the situation is different in Scotland. Here you must obtain an Air Weapon Certificate or Air Weapon Permit from the Police, or you can apply to add an air weapon to an existing Firearm or Shotgun Certificate.