The switch it for the light in the loft, not the extractor fan; that switch is the the bathroom. We had the light switch and the extractor fan (and all other electrical items) put in by a friend who is a professional electrical engineer .
The insulation was what was there when we got the house, and it passed the inspection we had done before we bought the house.
The house hasn't burnt down yet, so it seems ok.
I'm also thinking of investing in shares in the screw manufacturing industry :)