The operative who came round was astute and experienced and offered some useful tips. But it was a rushed visit - and it was emphasized that if we wanted another one we would be charged again. And not everything we were told worked out. We were advised that after 4 nights of consuming the poison, the mice would retire to their nest with hypothermia. Actually, and despite liking the poison, they were still around for ten days or so. We haven't seem them recently - but this may be due to their preference for the garden in warmer weather, as the man explained. It was recommended to us that we get something called an air-vent brick - easily available from Homebase or B & Q. Homebase said they hadn't sold such bricks for a year or so - and B & Q said that they sold the bricks only to 'trade'.