Two companies embroiled in the horsemeat scandal have revealed they are ready to sue further down the supply chain, as the investigation spreads across Europe and a government minister warns more contamination may be found in other food.

Speaking after emergency talks with industry leaders Owen Paterson, the Environment Secretary, said: "There may well be more bad results coming through, that's the point of doing this random analysis.

"This is a conspiracy against the public. Selling a product as beef, and including a lot of horse in it is fraud."

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He also said retailers hold the "ultimate responsibility" for making sure that horsemeat is not in their products.

The Food Standards Authority (FSA) have asked retailers and processors to test all their processed beef products to make sure they are what they say they are, with the results expected by next Friday.

Findus, whose "beef" lasagne was found to contain up to 100 per cent horse DNA, is preparing a legal case against whoever is found to have caused the contamination. In a statement, the firm said: "Findus is taking legal advice about the grounds for pursuing a case against its suppliers, regarding what they believe is their suppliers’ failure to meet contractual obligations about product integrity.

"The early results from Findus UK’s internal investigation strongly suggests that the horsemeat contamination in Beef Lasagne was not accidental."

The Trading Standards Institute has said the discovery of such high levels of horse meat suggests "deliberate fraudulent activity," and Scotland Yard said officers met the FSA over the scandal, although there is currently no official police investigation.

And Spanghero, the French company who supplied the meat for the lasagne, announced they will sue their Romanian suppliers.

The firm's President Bartholemy Aguerre said today: "We bought European origin beef and we resold it. If it really is horsemeat, we are going to go after the Romanian supplier." He did not disclose the name of the supplier.

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The lasagnes, as well as similarly contaminated ready meals sold by the budget supermarket Aldi, were supplied by by French frozen food giant Comigel. The meat packed at Comigel's Luxembourg factory, where the contamination originated, came from Spanghero's plant in south-west France.

It has also been revealed that 20 months ago the factory was at the centre of a major E.coli scare.

Inspectors had feared the Spanghero factory had churned out 12 tonnes of meat harbouring the potentially fatal bacteria.

Spanghero told the Daily Telegraph it had been given a clean bill of health following the E.Coli scare, with a source saying: "The beef was destroyed as a precaution but it did not threaten anybody’s health."

A criminal investigation is ongoing, and Mr Paterson said: "I've got a nasty feeling it's actually a criminal conspiracy.

"And that's why it's quite right for the FSA to engage the Metropolitan Police who are working with other police forces across the mainland of Europe."

Findus has also had to reiterate that it only learned this month about the contamination, which could have begun as early as August 2012. This followed accusations that it had known earlier but failed to tell regulators.

Yesterday Aldi said it felt "angry and let down" over the horsemeat content in their products.

Prime Minister David Cameron has said the matter is "shocking" and "completely unacceptable".

Labour leader Ed Miliband described the situation as "appalling".

He added: "I think people in the country will be quite shocked that horse meat has been in the food that they have been innocently buying.

"The Government has got to get a grip on this situation."