An investigation is under way to try to discover how a banned antibacterial
drug was found in organic chicken processed at a Northern Ireland factory.
Contaminated chicken has been supplied to supermarkets
Traces of nitrofuran - which increases the risk of cancer - were found in some chickens processed at Moy Park in County Tyrone during a routine check.
The company said 20,000 contaminated birds from one farm had been sold by Tesco, Waitrose and Morrisons throughout the UK.
However, Moy Park spokesman Gareth Jones stressed the risk to humans was very low.
"The apparent risk is close to zero, " he said. "You have to eat it over a long period and a lot of it."
The Dungannon-based factory is working closely with the Department of Agriculture to find the source of the contamination.
"Moy Park has extraordinarily high controls and standards and even still something like this can creep through," he said.
"We're looking now at the possibility of the farm, because organic birds are reared outdoors.
"So it could be some incursion from outdoors, we're looking at soil, the grass, chemicals used to clean the houses... everything needs to be looked at."
He said an area also being checked was possible contamination of ingredients in the chicken feed, but believes that is very unlikely.
The company have advised anyone who bought an organic chicken with a sell-by date between 8 and 14 October, to either bring it back to the shop or destroy it themselves.
"If people have eaten one, hopefully they will be assured that it's a one-off incident and we are deeply sorry for the distress caused.
"Directly we know what happened and why it happened, we'll be able to put a stop on it."
The Food Standards Agency also said the risk was low, but urged people not to eat the chicken.
An agency spokesman said: "All these chicken products are past their use by dates, so no-one should have any left in their fridge.
"They are no longer on sale in supermarkets. However, anyone who has frozen any of this chicken should not eat it."
Under EU law, it is illegal to use nitrofurans in food producing animals because of the cancer risk.
The problem came to light during routine tests carried out by the Department of Agriculture and Rural Development.
The affected products are:
- Fresh Organic British Chicken two boneless breasts (Brand - Waitrose).
- Fresh Organic British Chicken mini fillets (Waitrose).
- Fresh Organic British Chicken two breast fillets (Waitrose).
- Fresh Organic British Chicken four thighs (Waitrose).
- Fresh Organic British Chicken four drumsticks (Waitrose).
- Fresh Organic British Chicken two legs (Waitrose).
- Fresh Organic British Chicken four wings (Waitrose).
- Fresh Organic British Chicken without giblets grade A (Waitrose).
- Organic Fresh Chicken two skinless breast fillets (Tesco).
- Organic Fresh Chicken drumsticks (Tesco).
- Organic Fresh Chicken thighs (Tesco).
- Organic Whole Chicken (Tesco).
- Organic Chicken (Moy Park).
- Organic Chicken two leg portions (Moy Park).
- Organic Free Range Chicken without giblets (Morrisons).