Rentokill have new humane rodent killers, they are an electronic box, with a tunnel in it, mouse runs into tunnel, is detected by electronis in box, box snaps shut, and mouse is gassed by Co2, dies instantly and painlessy.
amazing piece of kit, very cleverley desigend, the local Rentokil bloke demonstrated them to me a couple of weeks ago,
not sure if they are available to the general public to buy, but worth checking.