People are being warned not to eat certain batches of organic free range chicken after it was contaminated by a banned veterinary medicine.
23,000 tonnes of contaminated chicken has been supplied to supermarkets
Up to 23 tonnes of the affected chicken has been distributed to supermarkets in the UK from a Northern Ireland farm.
The chicken contaminated by nitrofurans - which increases the risk of cancer - has been sold by Tesco, Waitrose and Morrisons and under the brand Moy Park.
The Food Standards Agency said the risk from eating the chickens was low.
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.
"They should throw it away or return it to the retailer where they bought it for a refund."
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 food was supplied to supermarkets by Moy Park, a food processing company based in Northern Ireland.
It has been sold as whole birds and chicken pieces.
An investigation is under way to establish how the chicken became infected.
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).