The tablets, manufactured by the Wallis Laboratory in Luton, Bedfordshire, have been sent out to Tesco, Unichem and the Co-op already for distribution nationwide.

The 16 and 32 tablet packets all carry the stores' own brand names and an expiry date of July 2001. Around 400,000 are thought to be on the stores' shelves and another 100,000 may still be in their warehouses.

Incorrect

The instructions on the packets are incorrect. They say that children under 12 should be given a half to one tablet every four hours.

They should say that children between six and 12 should be given a half to one tablet every four hours, but that not more than four doses should be administered in any 24-hour period.

The main health concern is that parents might give tablets to children under six. Health experts say children are generally less susceptible to the damaging effects of paracetamol than adults.

However, an overdose of the pills could lead to liver problems and ultimately prove fatal for very young children, who generally take painkillers in syrup rather than pill form.

The laboratory says there is nothing wrong with the pills themselves and an investigation into the matter is under way.

Misleading

Mayur Gohil, quality and technical manager at the laboratory, said the "misleading" wording on the paracetamol packets was noticed on Tuesday night and the Medicines Control Agency (MCA) was alerted.

The laboratory and the MCA decided on the recall action. Mr Gohil said all the national newspapers had been informed of the possible dangers of the drug.

"We are still carrying out our investigation into why this happened, but our top priority is public safety," he said.