The chicken was sold to retailers

Professor Hugh Pennington, head of the University of Aberdeen's Department of Medical Microbiology, said the contaminated poultry would have been riddled with salmonella and campylobacter.

The bacteria was certain to have spread rapidly through the already-condemned meat - as it was stored in appalling conditions at the premises of Denby Poultry Products, in Derbyshire, he said.

The premises were infested with rats and pools of sewage collected on the factory floor, Nottingham Crown Court heard.

Rat-infested

"In this case salmonella would have been a particular risk, as it is discovered in high quality chicken, let alone that which has already been condemned," said Mr Pennington, who chaired a government inquiry into the 1996 Central Scotland E coli outbreak.

"With the meat stored in rat-infested premises, perhaps on occasion even left outside, the conditions are perfect for cross contamination and infection.

Salmonella can increase one million-fold overnight, so the disease would have spread rapidly Hugh Pennington Microbiologist Charges are dropped

Derbyshire Police carried out a major surveillance operation into the scam following an anonymous tip-off to environmental health officers, uncovering a trail of deception that stretched back to 1995 and involved around 600 customers.

Peter Roberts, 68, known as "Maggot Pete" who ran the Denby firm between 1994 and 2000, was convicted of the fraud in his absence on Wednesday after fleeing before the start of the trial.

Five other pleaded guilty to conspiracy to defraud at earlier hearings, while charges against three others were dropped and one man was found not guilty.

Mr Pennington said: "Those eating the meat would have been subjecting themselves to a melange of bacteria, rat urine and faeces, including salmonella and campylobacter."

Elderly at risk

The meat was shipped in unrefrigerated vans, which workers said were riddled with maggots.

"Once the chicken was loaded together on the vans, it would start to contaminate even more," he said.

"Salmonella can increase one million-fold overnight, so the disease would have spread rapidly over the course of the long journeys across the country."

He claimed that while people who properly cooked the meat should have been at minimal risk, older and poorly individuals would not put up the same resistance to the infections.

"In most cases people would not have suffered if they cooked the chicken properly," said Mr Pennington.

"Where this meat was wrapped in breadcrumbs, the appearance or smell would have been disguised and consumers are unlikely to have even known the meat was unfit.