Europe's largest poultry company Bernard Matthews has been accused of importing and exporting poultry to and from protection zones established around bird flu outbreaks in Hungary and the UK.

In determining how the deadly H5N1 virus made its way to Bernard Matthews' Suffolk farm, the Department for Environment, Food and Rural Affairs (Defra) told just-food that it is considering the possibility that the company could have carried it into the country with partially processed turkeys imported from Hungary, where the virus originated.

Media reports have focused on this facet of the investigation, claiming that Bernard Matthews imported meat from a slaughterhouse just 30 miles from the Hungarian bird flu outbreak.

Speaking to reporters over the weekend, Environment Minister Ben Bradshaw did not rule out the possibility that the company could face prosecution. He said: "There has clearly been a lapse in biosecurity, otherwise the avian flu virus would not have got into that poultry shed. We do have law on biosecurity and law on animal health which is vigorously implemented in this country."

Defra told just-food that until its investigation was completed the department was unwilling to "name names". "We were aware that they were importing products from Hungary, but the exact nature of those imports is still under investigation. It is an important part of our inquiry and until we have reached a clear conclusion we are not finger pointing," a Defra spokesperson said.

Defra has also started looking into claims made by Hungary's deputy chief vet, Lajos Bognar, that Bernard Matthews exported poultry products from the Suffolk farm at the centre of the UK outbreak after the disease was identified. According to Bognar, six trucks transporting products from the turkey farm arrived in Hungary last week.

Defra told just-food that although strict rules designed to prevent the spread of the disease came into effect after its detection, various products are exempt from the movement ban. Live birds, eggs and carcasses cannot be moved from infected sites, but processed meat in storage can be transported.

"They are allowed to export products from the restriction zone under certain conditions. For example, heat treated or cooked products can be exported. We are investigating whether Bernard Matthews met these conditions," Defra said.

Bernard Matthews told just-food that it follows food safety regulations scrupulously and that it is cooperating fully with the investigation.