So it turns out boy cat aged 20 months is quite good at catching mice. We've had a couple of live ones running round downstairs while he's sleeping upstairs (presumable "lost" after bringing them in?), a couple of dead ones left in the middle of the kitchen and lounge and one poor unfortunate who crawled behind a cupboard to expire. All of these I fully accept as generous gifts and part and parcel of having boy cat. However...we have now had 6 episodes of being woken up in the early hours by boy cat running round the bedroom accompanied by squeaking where he is tossing a mouse in the air and pouncing on it 
He is then very upset when the mouse is removed and has started growling.
He has a cat flap which he loves and we give him full access to this and the whole house, accepting the dirty footprints and soaking wet fur as an acceptable trade off for the joys of waking up with boy cat snuggled on your bed. He loves being outside and is literally out in all weather. Snow and rain don't put him off at all and he happily sits on the patio in torrential rain. We live in a cul de sac, not rural at all and never see mice other than when he brings them in.
I imagine our only options to prevent the nighttime mouse escapades are to either lock him in the kitchen where he has access to the cat flap, food, water, litter tray (which he currently doesn't use) and a playroom with carpet, sofa, big windows or to lock the cat flap at night giving him access to the whole house. I don't think he'll like either option and he's otherwise such a loving, contented, well behaved boy that I don't want to upset him or risk any unwanted protest behaviour either.
So before we have to go all drastic, is there any option I'm missing or way of discouraging his nighttime mouse antics? Photo for reference of the delightful critter.