We live in a 200 year old stone cottage (they're very common round here) and the walls are really rubble-filled double piles of stones. One disadvantage, amongst many, is that they provide spacious accommodation for small rodents from time to time. We don't usually have a problem in warmer weather; mice infestation is normally a Winter problem and relatively minor. Not so right now.

As Angharad doesn't seem to have spotted this yet - or, if she has, not got round to posting - here's an article in today's Guardian Education supplement that may be of interest here.