But Advocates for Animals responded to the criticisms by stating that NFUS is simply deflecting attention away from the animal welfare issues at hand, as its investigators observed strict bio-security practices at all times.

The animal welfare organisation claims that Glenrath Farms, owned by John Campbell, breached Scottish animal welfare regulations by overstocking its cages and not removing dead birds on a daily basis. Mr Campbell has denied the allegations, stating that Glenrath Farms labours stringent welfare standards.

In March and April 2007, the Advocates for Animals investigator made three visits to the same poultry shed, housing 59,000 layers, at Whim Poultry Farm in West Linton, Peeblesshire. There are three units at the site, each holding 44,000, 59,000 and 88,000 birds.

animal welfare regulations, cages must hold a maximum of five birds and dead birds must be removed daily. But the investigator claims he saw a high incidence of cages containing up to eight birds, plus high rates of feather loss, foot deformities and dead or decomposing birds.

Ross Minett, director of Advocates for Animals, said: Intensive farmers may well prefer the public not to be able to see how animals are treated behind the closed doors of factory farms. That is why we fully defend investigations such as this which are in the public interest. I think the public will see through this.