I had mice in my kitchen not long ago, phoned the pest control people, they bought some traps and laced the bait with peanut butter. After 3 days mice removed. Some of my neighbours had reported mice in their kitchens and living rooms too, so the pest control people were around for some considerable time. The cause? well one theory was that a nest had been disturbed due to building work which my neighbour to my left had been having done as he was having a 3 square metre high kitchen built ( this replaced a lovely conservatory that my old neighbour had done some years before)