I'd like to add my recommendation for CHS Pest Control. I've just had Colin around for the second time to check if his intervention in terms of getting rid of rats had been successful. Indeed it had! Colin is incredibly knowledgeable and practiced at understanding rodents and old buildings. He is thorough, uses poison that does not leave stinking corpses, and is good at minor repairs and changes to stop rats getting back into the house, e.g. when they dig down the side of a building. If you want someone who can respond quickly and is reliable, he is the man to go to.
