Swarms of mutant flies, immune to household insecticides, have been invading homes in Twyford, near Winchester.

Mainly hitting residents in Bourne Lane, Bourne Fields and Hazeley Road, the infestation has been traced to nearby Humphrey Farms, where chicken sheds are being shut down. Beetles are normally used to eat fly larvae, but once the birds were removed and the sheds became cold, the beetles died off and a large number of maggots hatched out as flies.

Because the sheds have already been treated with commercial pesticides, the flies are immune to ordinary domestic fly spray and should be tackled by more conventional methods like fly paper.

A large number of calls were made to Winchester environmental health officers by concerned villagers who first noticed the swarms of insects almost two weeks ago.

Scientific officer, Phil Tidridge said: "It was a problem and it was very unpleasant. The trouble is flies have more of an effect this time of year because they tend to head inside people's homes.

"The good news is the last two chicken sheds will be closed by the end of January, so there will be no more flies. Humphrey's have not done anything illegal by releasing the first lot of flies and, following our inspections, we are happy things are now being controlled as they should be."

Environmental health staff will continue to monitor the situation until the last two sheds are closed down in January to make sure there are no further infestations.