I was plagued with them in my flat a couple of years ago. I was almost demented with it; they were scurrying about the bedroom all night, leaving deposits on my pillows, it was awful. I tried snappy traps, ultrasonic repellers and humane traps, but they kept coming back.
You need to make the place as unattractive to them as possible which means ensuring there is no food for them - all food needs to be bagged or boxed or otherwise stored in a secure container and kept in the fridge or a cupboard. Don't leave dirty dishes lying around, wash them up at least before you go to bed. Block up all the tiny holes and cracks you can with something they won't chew through - steel wool, or polyfilla mixed with ground glass. A pregnant mouse can squeeze through a hole the size of a pencil end, so do even the tiniest gaps.
And - my piece de resistance - use peppermint essential oil. Buy yourself a big bottle and pour it liberally around the house, particularly on the places you know they use as routes. Do it at least twice a day to start with then decrease it and once they've gone, you can drop it down to once a week and then just whenever you remember. They hate the smell and they don't like walking across a pepperminty area - I saw it with my own eyes a couple of years ago when one of the little gits started to walk across my newly pepperminted hearth, squeaked, shot up in the air and ran away. Haven't had sight nor sound of one since.
Your house will smell like a humbug factory for a while though.
