Two senior managers at a subsidiary of a French restaurant chain, Buffalo Grill, are being formally investigated for manslaughter as part of an inquiry into illegal imports of British beef.

The chain's chairman and chief executive, Christian Picart, and a fourth manager are due to be questioned by a judge on Thursday.

The facts are not established. There is not a shadow of a solid element in this case Jean-Pierre Versini-Campichi Buffalo Grill lawyer

It is alleged that the Buffalo Grill chain continued serving beef from Britain after it was banned in the European Union and that this may have been the cause of cases of the human form of mad cow disease (BSE), known as variant CJD.

Also on Thursday, the French Government announced restaurants serving beef would have to display on their menus the origin of the beef that they use.

When France lifted a six-year ban on British beef in October after a mad cow scare, the government announced it would pass a law requiring restaurants to say where their meat came from.

It was illegal to import any beef from Britain between 1996 and 2002 because of the threat of BSE.

The arrests are part of a wider French inquiry into the deaths of at least four people in France from variant CJD that is passed onto humans by eating beef.

A recent report said around 300 people could eventually be diagnosed with the disease.

The detentions were ordered by a judge who since December 2000 has been in charge of a judicial inquiry into "involuntary manslaughter and damages and endangering the lives of others" after the families of the victims filed a lawsuit.

The investigation was aimed mostly at the Buffalo Grill subsidiary, Districoupe, which police suspect may have illegally imported beef from Britain.

Denial

The Buffalo Grill lawyer on Wednesday hotly denied allegations against the chain, saying they were made by three former members of staff who failed to produce material proof of their claims.

"The facts are not established. There is not a shadow of a solid element in this case," said Jean-Pierre Versini-Campichi.

The lawyer for the families of the four victims has said no link could be made between the deaths and illegally imported meat because the disease's five-year incubation period means the victims were probably contaminated before the 1996 ban.

The investigation in the case found that two of the four victims had dined at a Buffalo Grill restaurant before developing the disease.

US-style chain

After spending several years in the United States, chain manager Picart opened his first restaurant in France in 1980, where he hoped the US "steak house" concept would catch on.

By the end of 2001 Buffalo Grill had cornered half of the grilled-meat restaurant sector, eclipsing the rival Hippopotamus chain.

After the news, shares in the chain crashed by more than 90% on Wednesday before being suspended altogether.