After some quality advice on this forum I've been locking the cat flap overnight to try and prevent dawn/dusk hunting as we were having a lot of mice brought in, despite living in a very urban (not sure where they're coming from) area.
Sadly the furry monster is still bringing them in and losing them. We regularly find a rogue mouse trotting round and then have to go hunting. It's a nightmare!
Any suggestions to avoid this or is it just part and parcel of cat ownership? 
Cat tax - like butter wouldn't melt...