also remove the dead birds, mice and squirrels that they feed on.
I have recently been using Cypermethrin insecticides, they are usually sold as sprays for ants and cockroaches, or against moths. They leave a film of dried poison on hard surfaces, that kills insects through their feet when they walk on it. You would have to get the loft clean first as I doubt it would work well on a layer of dust.
I got some "Doff" brand in Tescos at £1 per litre spray bottle; most brands are more expensive, but Wilkinson's are selling some off at half price in their Garden shelf clearance.
It seems to me to be very effective, and I understand it is less environmentally damaging than other insecticides. the bottle indicates you can also spray it into the air like an aerosol against flies and wasps, so that will help.
There is also a variety of fly I used to get in a country attic that comes in through cracks, I forget what it is, but they seem to be able to smell where they were in previous years, perhaps they come in to try to hibernate. I think you have to clean them up very thoroughly to prevent another lot coming in. I used to hoover them up in winter.
