Bernard Matthew turkey products may have to be withdrawn from the shelves in an effort to prevent bird flu spreading.

Even though the meat, if properly cooked, poses no risk to human health the Food Standards Agency is investigating whether turkey meat infected with avian flu has entered Britain's shops because of the risk of the disease being passed to other animals.

The agency said it was keen to remove products carrying the virus from the food chain to stop its transfer to Britain's wild bird population.

"The investigation has just begun," said a spokesman. "If we find infected meat at the end of the food chain we will take appropriate action because it would be illegal."

This evening the Sainsbury's supermarket chain reported a 10 per cent fall in poultry sales this week, although the retailer said that the poor weather could have been to blame.

News of the investigation came as the Government's chief scientist said that Britain's first case of the lethal H5N1 strain of bird flu, discovered at a Bernard Matthews farm in Suffolk last week, was probably brought to the country in a delivery of turkey meat from Hungary.

Bernard Matthews, Britain's largest turkey producer, imports 37 tonnes of partly-processed turkey meat from Hungary every week but has strenuously denied bringing in any poultry from a region of the country where H5N1 was found late last month.

But today the company was confronted by the news that the DNA of the virus found in the UK is a near identical match with the recent Hungarian strain, leading Sir David King, the Government’s chief scientist, to say that infection from Hungary was the "most likely scenario".

Earlier this week, Bernard Matthews, a £400-million-a-year business, said there "wasn’t a remote possibility" of its products being infected by the Hungarian outbreak. But since then the company has come under scrutiny for allegedly leaving processed poultry outside its sheds and for possible lapses in "bio-security" at its farm at Holton.

Ben Bradshaw, the Animal Welfare minister, declined to comment on the alleged breaches today "because it’s possible that legal action could follow".

Sir David said his immediate concern was to find out whether the bird flu infection, which has led to the culling of 160,000 birds, had managed to spread beyond the confines of the Bernard Matthews farm. If the virus managed to spread from partly-processed turkey meat brought from Hungary, it was necessary to find out whether it could spread from other turkey products now on their way to supermarket shelves.

"I think that is exactly what the Food Standards Agency will be looking at now," he told Channel 4 News this evening.

"That sort of direct transfer is my biggest worry at the moment because the transfer could occur through, for example, wild animals and wild birds so the real concern now is whether or not the virus is isolated to the birds that have been culled or whether it has moved beyond that," he said.

"My bigger worry is that it might have got into the wild bird population. We need to keep a very close eye on that."

News of the likely spread of bird flu through the lorries and battery farms of Britain's £3.4 billion poultry industry led to statements from organic farmers and environmental groups today.

The Soil Association, which represents and advises organic farmers, said it was time to stop suggesting that wild and free-range birds remain the most likely vectors of the disease:

"Such claims...have the whiff of vested interests seeking to divert attention from the international movement of eggs, birds and poultry products as a key suspect in the global spread and exacerbation of the disease," the group said.

Meanwhile the Royal Society for the Protection of Birds, the country's largest wildlife conservation charity, reported that it had seen no sign of a gradual spread of the H5N1 strain through wild bird migration across Europe this winter.

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