had the same problem with a house in cornwall,bluebottle,s in the bedroom mainly.we got a firm in to find the cause,they were coming though the soffitsand hibernateing in the loft.they sprayed all the gaps at the soffits ,and loft and bought a u/v flytrap which was put on a timer,2 hours a week.we never did find the source ,but did cure the problem. hope this helps...mike