The Department for Environment, Food and Rural Affairs was last night investigating claims that poultry meat from the contaminated Bernard Matthews site in Suffolk had been exported to Hungary after the outbreak of bird flu was identified. Six trucks of poultry products from the Suffolk farm arrived in Hungary on Thursday, according to the country's deputy chief vet, Lajos Bognar, despite the imposition of rigid quarantine rules following the H5N1 outbreak 10 days ago.

The development came as the government tried to defend its handling of imports from Hungary after the Suffolk outbreak. The apparent movement of meat in and out of the country despite the concerns has raised questions about the response to the bird flu discovery.

Defra confirmed last night it was investigating the apparent exports, adding that they could have been legal if the meat had already been processed. "Depending on the type of product, date of slaughter and which farm it originated on, it is possible that poultry product from the Suffolk plant could have met the licensing requirements for movement outside the restricted area," a spokeswoman said.

Dr Bognar said the meat had left the plant in Holton and arrived back at Bernard Matthews's Hungarian plant on either Wednesday or Thursday. "I can say that from the protection zone, from the UK, six trucks arrived from there last week, to Hungary," he told Channel 4 news.

It was reported that the lorries had left the British plant for Hungary under a special licence issued to Bernard Matthews.

The firm last night reiterated that it had suspended movements between the UK and Hungary, and said it was helping Defra with its investigations.

As for the Hungarian poultry imports, David Miliband, the environment secretary, said yesterday that a ban on imports would breach EU rules and might provoke retaliation against the British poultry industry. He said he would only have imposed a ban if vets had told him this was a "sensible" step to protect public health. The National Farmers' Union and the government's chief scientist, Professor Sir David King, say an import ban should be considered.

Investigators, who are now focusing on turkey meat legally imported from an area of Hungary outside an exclusion zone as the possible source of infection, are still trying to determine whether contaminated food from the Bernard Matthews site has been on sale in Britain.