I don't know why I didn't think of this before - but the simplicity of the answer has staggered me!!! To prevent the cat from dragging small animals into the house during the night - simply shut the cat flap!!!! That way she has to leave any carcasses outside!!!! No doubt she's got a flat area on her head from running and headbutting the cat flap door, expecting it to open...and I may have to re-address the issue as the nights become colder - but for now it seems like an ideal solution. I've just opened it again to let her back in and you should have seen the look she gave me.