Batches of lamb containing illegal veterinary drug residues that can make consumers ill are on sale in supermarkets.

There is a particular danger to any pregnant woman who has been exposed to regular doses of the drug, as high residue levels can affect foetal development. The Food Standards Agency has ordered a search and confiscation of this meat to protect consumer health.

The agency has begun an investigation to find out how this meat was able to enter the food chain and was supplied to leading supermarkets and other retailers. This could result in a criminal prosecution.

Almost 2,500kg (5,510lb) of suspect lamb is known to have entered the food chain, but the agency believes that there could be more. Half has already been identified and various lamb cuts and joints removed from sale at Asda stores nationwide.

Another consignment is being held in cold stores at Morrisons. The cash-and-carry company Macro issued a recall of affected batches of lambs’ kidneys and liver yesterday.

The rest has been mixed with other batches of lamb destined for the wholesale trade, and enforcement officers are having to track tonnes of meat consignments in a painstaking audit trail.

The food watchdog sent out a letter yesterday to all sectors of the livestock industry, including the Meat Hygiene Service (MHS), alerting them about illicit meat with high residues at abattoirs and meat-cutting plants.

Auctioneers at livestock markets are urged to be particularly vigilant for there is concern that breeding sheep are being bought up for meat.

The price of these animals has collapsed after the foot-and-mouth and bluetongue outbreaks and with the industry facing cashflow problems there is suspicion that some suppliers may be tempted to make quick profits by substituting cheaper breeding animals instead of buying lambs ready for the table. The price difference is about £6 to £8 an animal.

The National Farmers’ Union and the National Sheep Association are enraged. They need to maintain consumer confidence in the meat to deal with the glut of lamb on the market.

The Times has learnt that the alarm was raised last week when a trading standards officer who attended a number of Cumbria livestock auctions learnt that an abattoir buyer had bought up significant amounts of breeding sheep that were not intended for the food chain. The officer was concerned because he could smell sheep dip on the fleece of some animals and was worried that they would be slaughtered for meat in contravention of the law covering drug residues.

Treated animals can be sold eventually as meat after a safe period when drugs have passed through them. The officer was given reassurances that the animals were not being slaughtered for meat but nevertheless sent a general warning to the MHS.

A vet who works for the MHS at Welsh Country Foods in Anglesey picked up the alert and last Wednesday detected the smell of sheep dip on animals. She quarantined hundreds of animals, refused to allow them to be sold for human consumption and called in the local trading standards officers. A paper trail from the auctions showed they had been bought at Cumbrian markets. There was immediate concern because Welsh Country Foods is a subsidiary of Grampian Foods, a leading meat distributor that also supplies the bulk of Asda’s meat.

Officers visited farmers who reared the sheep and checks on farm records showed that some animals had been treated with organophosphate sheep dips, some injected with dormectin, an antiparasitic drug, and some had received both treatments. There was alarm because it takes 30 to 35 days after an animal is being treated with sheep dip for meat to be safe, and there must be a 70-day period before animals treated with dormectin can be sold as meat. Yet these animals were being slaughtered two weeks after being treated. The abattoir informed the FSA about the problem immediately and asked for advice. The company then supplied the agency with details of batches and consignments.

There was particular concern about dormectin because in laboratory tests rats have fallen sick after being exposed to the drug.

Paul Roger, a former president of the Sheep Veterinary Society, said: “I am concerned if there is a missing batch of meat still out there.”

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