Bernard Matthews is under investigation by the Government amid concerns that the company has imported poultry from inside an avian flu exclusion zone in Hungary, it emerged last night.

The company, Britain’s largest turkey producer, is also being investigated for breaking EU hygiene regulations by leaving processed poultry outside sheds on its food processing site at Suffolk, where a lethal strain of bird flu was detected last week, according to senior Whitehall sources.

Another three of the units of the 22 at the Bernard Matthews farm in Holton, Suffolk, have tested positive for H5N1, it emerged last night, raising fears that the virus was more entrenched than originally hoped. Government scientists will be looking at establishing how the virus spread from hut to hut, or whether all four huts suffered separate, independent infections from the same source.

The Government has found that the strain of the virus in both countries may well be identical. If the imported birds were infected with the H5N1 strain, this virus could easily have been picked up by wild birds and rats, which may have contaminated the chicks in one of the 22 sheds on the site at Holton.

The initial report by veterinary scientists into the conditions of the plant where 160,000 turkey chicks were gassed this week may prove serious for Bernard Matthews and his £400 million-a-year business.

The investigation also poses questions about the practices employed by the £3.4 billion British poultry industry. Bernard Matthews agreed last night to suspend all further trade between Hungary and the UK. The company said that it was cooperating fully with the investigation. A spokesman said: “We want to reassure consumers that Bernard Matthews products are safe to eat.”

Bart Dalla Mura, the company’s commercial director, said on Monday that there “wasn’t a remote possibility” that the bird flu outbreaks could be linked.

State veterinary scientists want to establish if any birds processed at the company’s Hungarian factories originated in the Csongrad region where the H5N1 strain was confirmed at a commercial goose farm on January 24. A second outbreak in that area was confirmed on January 30.

Under European regulations no birds should be moved in a 3km zone around infected farms and in the further 10km surveillance zone.

But it has now emerged that 37 tonnes of partly processed turkeys have been arriving in Britain from Bernard Matthews Hungarian plants every week. A delivery arrived at the plant just a couple of days before January 27, when workers first spotted signs of illness in the eight-week-old chicks.

This detail is understood to have been withheld on grounds of commercial confidentiality.

Scientists must also ascertain whether the company imported birds from these infected regions in breach of Brussels rules. The Hungarian Government said that they imposed strict controls in the areas and this was approved by Brussels.

The inquiry is being conducted jointly by the Department for Environment, Food and Rural Affairs, the Food Standards Agency and the Health Protection Agency. The focus is on links between the company’s operation in Holton and Hungary.

The H5N1 virus can survive for five to thirty-five days. Experts said that the chilling and freezing process could extend the life of the flu strain. In the open air the virus could last seven to ten days.

The scientists’ findings are certain to be serious for Bernard Matthews, which intitially denied any links between Hungary and the UK. Further tests are being made on carcasses in a pile of processed poultry waste found outside the plant. If the turkeys were infected the virus could also last three to seven days and could then be passed on to wild birds.

Government sources ruled out any concerns for the moment about any worker bringing the virus to the UK on shoes or boots. The company is likely to face legal action for breaches of biosecurity rules.

Whitehall sources last night confirmed that it was still “early days” for the inquiry.

But wildlife experts were privately delighted by the way that the Government was scrutinising the poultry industry.

Conservationists had insisted that it was impossible to blame the arrival of the H5N1 virus into commercial poultry on wild birds, when not one bird had been found with the disease in the UK or northern Europe.

Peter Ainsworth, Conservative Rural Affairs spokesman, said last night: “It always seemed unlikely that avian flu arrived in Suffolk via the wild bird population, since there has to date been no evidence of infected wild birds. Bernard Matthews have some very serious questions to answer about . . . the version of events they have told.”

EU regulations ban imports of live poultry from areas that may harbour bird flu. Countries must prevent poultry movement from infected areas.

In the light of foot-and-mouth and the bird-flu scare, Defra have also issued strict guidelines for biosecurity.

The first defence against infection is wearing clean overalls and footwear when entering poultry farms.

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