Newly released test results have revealed much more of a toxic chemical in tainted animal feed than previously thought.

The tests at the plant in northern Germany where the contamination happened revealed levels of dioxin at 77 times the permitted level. The plant produces fats to be used in industrial processes like paper-making as well as to enrich feeds for animals.

The dioxin-laden industrial substance went into the animal feed ingredient.

Initially the scare was confined to Germany, but then it emerged that a batch of affected eggs had been exported to the Netherlands for processing and from there to Britain. The processed eggs were destined for use in the production of a variety of foodstuffs including mayonnaise, cakes and quiches.

Some 4,700 German farms have been banned from making deliveries after tests at the Harles und Jentzsch plant in the state of Schleswig-Holstein. The firm was found to have supplied 25 animal feed makers with 3,000 tonnes of contaminated fat. German officials say the farm measures are only a precaution.

Authorities believe some 150,000 tons of feed for poultry and swine containing the fat have been fed to livestock across the country. South Korea has reacted by blocking imports of German pork and poultry products.

According to Schleswig-Holstein's agriculture ministry, the contaminated fats contained 58 nanograms of dioxin per kilogram. The acceptable limit is 0.75 nanograms of dioxin per kilogram. The ministry has confirmed that tests as far back as March last year showed high levels of dioxins, but it was unaware of the results until late December.

Those results have now been seized as evidence by prosecutors.

"The first indications point to a high level of illegal activity," said a spokesman for German Agriculture Minister Ilse Aigner on Friday.

"There are indications that the company was not even officially registered, in order not to expose itself to official controls," he added.

A doctor from the town of Havixbeck, near Munster, has lodged a criminal complaint of attempted murder and severe injury against Harles und Jentzsch, saying the company had acted out of greed.

German agriculture officials will brief their European Union counterparts next week and the incident could lead to new rules on animal feed.

Dioxins are toxins formed by industrial processes and waste burning. They have been shown to contribute to higher cancer rates and to affect pregnant women.