Cooked turkey products were exported from the Suffolk site where bird flu was found after the virus had broken out, Hungary's chief vet has claimed.
Exports from the Suffolk plant may have been legal, Defra said
Lajos Bognar said Bernard Matthews sent some of the food to Hungary - where the UK outbreak may have originated.
The meat from the Holton plant arrived at the firm's Hungarian site on either Wednesday or Thursday, he said.
The British government said the EU allowed cooked poultry to be exported from an exclusion zone.
1 Feb: Vets called to Bernard Matthews farm in Suffolk after turkeys die
3 Feb: Vets confirm H5N1 strain
5 Feb: Environment minister says most likely cause is from wild bird, but other possibilities being investigated
8 Feb: Government vet suggests turkey meat from Hungary may be to blame. Bernard Matthews denies link
9 Feb: FSA examines whether infected meat may have entered food chain
10 Feb: Supermarkets deny there has been a slump in poultry sales
"I can say that from the protection zone, from the UK, six trucks arrived from there last week, to Hungary," Mr Bognar told Channel 4.
The Bernard Matthews site at Upper Holton in Suffolk has both a farm and a poultry processing unit.
The farm was shut down immediately after the outbreak was suspected, but much of the processing business continued as usual.
That means cooked meat was transported from there across Britain and further afield - to countries including Hungary.
The Department of Agriculture Food and Rural Affairs (Defra) said their investigation would look at all movements.
But a Defra spokesman said exporting cooked poultry from an exclusion zone was allowed under European rules.
"It is possible that poultry product from the Suffolk plant could have met the licensing requirements for movement outside the restricted area," he said.
The virus is quickly destroyed by heat.
Opposition politicians and some scientists say the government and Bernard Matthews need to be much more open about exactly what is coming and going from the infected premises.
Peter Ainsworth, the Conservative spokesman for rural affairs, told BBC Radio Five Live there had been "confusing advice" from government agencies since the bird flu outbreak
He added that this threatened to "turn a drama into a crisis".
MEP Neil Parish, who chairs the Agriculture and Rural Development Committee in the European Parliament, told BBC Radio 4's Today programme: "I think, from the exclusion zone you don't actually want anything going out.
"I mean this was cooked meat so therefore the risk was very low if at all, but of course actually moving the lorries in and out is ridiculous in this situation."
A Bernard Matthews spokesman said on Sunday a voluntary suspension of movements of its poultry products between the UK and Hungary, introduced last week, was still in place.
A company spokesman said on Sunday night the statement still stood and movements were still suspended.
But the company is reported to have imported turkey from the country in the days after the outbreak, despite the government suspecting Hungary was the source of the disease.
Channel 4 News reported lorries had also left the British plant for Hungary under a special licence issued to Bernard Matthews and arrived there three or four days ago.
But it claimed the decision to grant the licence would have been made before it was clear poultry products, rather than wild birds, were the likely source of the outbreak.
It said Hungarian vets were due to get the results on Monday of tests carried out on processed meat transported from the UK to the country after the British bird flu outbreak.
Currently EU rules mean Hungary cannot export any poultry from a 10km zone around the bird flu-hit area - but anybody outside the zone can continue to trade.
The Food Standards Agency is continuing to investigate whether infected products are on shop shelves, and has said a recall is possible if evidence of contamination is found.
The H5N1 virus, which causes bird flu, does not pose a large-scale threat to humans as it cannot pass easily from one person to another.
But experts fear the virus could mutate at some point in the future and trigger a flu pandemic, potentially putting millions of human lives at risk.