British police and regulators raided a slaughterhouse and a meat processor yesterday suspected of selling horsemeat as beef, expanding a Europe-wide scandal that has shocked consumers and exposed flawed food safety controls.
In Paris, French prosecutors opened a preliminary judicial investigation to determine whether fraud was committed in the growing scandal.
The prosecutor's office said a judicial inquiry had been opened in the northeastern city of Metz on Monday, but subsequently it was transferred to Paris, where national issues of food security are investigated.
In Britain, the raids on companies were the first by officials investigating horsemeat supplies in a country where the issue has angered consumers and led to several big retailers pulling contaminated products from their shelves.
While it is not illegal to sell horsemeat in Britain, eating it is virtually taboo. The British government said anyone found to have fraudulently sold horsemeat should be prosecuted.
"It is totally unacceptable if any business in the UK is defrauding the public by passing off horsemeat as beef," Britain's Environment Secretary Owen Paterson said.
"I expect the full force of the law to be brought down on anyone involved in this kind of activity."
The Food Standards Agency, the British regulator, said it had suspended operations at an abattoir in northern England and a meat processing company in Wales while it investigates whether they were involved in horsemeat being missold as beef for kebabs and burgers.
The scandal, affecting a growing number of European countries and retailers, began in Ireland when horsemeat was found in frozen beef burgers. The inquiry has implicated companies across Europe, from France and the Netherlands to Cyprus and Romania.
Britain's Paterson is due to meet European Union officials in Brussels today to discuss the issue.
The issue came to light on January 15 when routine tests by Irish authorities discovered horsemeat in beef burgers made by firms in Ireland and Britain and sold in supermarket chains including Tesco, Britain's biggest retailer.
Concern grew last week when the British unit of frozen foods group Findus began recalling its beef lasagne on advice from its French supplier, Comigel, after tests showed concentrations of horsemeat in a range from 60-100%.
In a separate development yesterday, upmarket British retailer Waitrose, part of the John Lewis group, withdrew packs of frozen beef meatballs after tests suggested they might contain pork.
"The meatballs are safe to eat but pork is not listed as an ingredient and should not be part of the recipe," it said.
Rogue suppliers are suspected of trying to increase their margins by passing off cheap horsemeat as more expensive beef.
Food experts say globalisation has helped the industry grow, but has also created a complex system which has fuelled the risk of adulteration through neglect or fraud.
Mark Woolfe, a former senior food safety official, said the European Commission's decision to reclassify a product which closely resembled mince as "mechanically separated meat" had forced suppliers to seek cheaper alternatives.
"Manufacturers who were using that for value products had to leave the UK food chain and go and look at overseas suppliers at a price similar to desinewed meat or even lower," he said.
In France, frozen food seller Picard became the latest French retailer to recall lasagne and other meals from its stores on Tuesday after discovering horsemeat in packaged foods advertised as beef.
An initial investigation by French authorities revealed that the horsemeat that made its way throughout the supply chain to Britain and France originated from a Romanian abattoir.
On Monday, Romania's prime minister denied that any Romanian companies had committed fraud in the affair.
More cases are expected to emerge during tests on processed beef products in Britain, with results due on Friday.