The company at the centre of the UK bird flu outbreak has defended its import methods as officials investigate whether the disease came from Hungary.
Partly-processed birds from Hungary were being trucked to Suffolk
Bernard Matthews said it transported meat products from its plant in Hungary but its records showed they were not from the infected bird flu zone.
Government vets now believe the H5N1 virus outbreak was transferred from other poultry and not wild birds.
The firm has halted Hungarian imports and exports as a precaution.
Bernard Matthews had trucked partly-processed turkey from Hungary to its plant in Holton, Suffolk, every week.
The company has a processing plant in Sarvar, in Hungary - about 160 miles away from Szentes, the centre of the Hungarian outbreak.
But commercial director Bart Dalla Mura defended the company's import practice, saying there were no restrictions on importing material from Hungary from outside restricted areas.
And he said the firm had not brought any poultry or meat products from inside the infected region into the country.
"We have made all our checks and they have come from nowhere near the restricted region. That is what our paperwork says to us."
He rejected suggestions that the firm had kept quiet about the imports.
Defra's Deputy Chief Veterinary Officer, Fred Landeg, said evidence now suggested the virus may have travelled from Hungary in meat products rather than entering the farm through migrating wild birds.
He said it appeared that the virus "may well be identical" to a strain found in Hungary earlier this year.
But he described the investigation as "like a jigsaw puzzle" and said it would take some time to complete and the results may not be conclusive.
"What we are in the middle of is a very complex epidemiological study, it is rather like a jigsaw puzzle. We are putting it together," he said.
"We may not get all the pieces and we may have to come to some conclusion on the balance of probabilities."
The government's chief scientist Sir David King told BBC Breakfast that the "most likely scenario" was that dead poultry from Hungary brought the H5N1 strain of bird flu to the UK.
"What we have is new data which indicates that the virus that is present in Suffolk is identical to the virus that was present in Hungary.
"My conclusion from that would be that this is a poultry-to-poultry infection rather than a wild bird to poultry infection."
Hungarian officials said that although there has been trade in "animal products" between the two branches of Bernard Matthews, it was "very unlikely" that avian flu could be spread by such processed and frozen meat.
Shadow environment secretary Peter Ainsworth has called on Defra to make a statement about the outbreak and investigation.
"I think the question for government is where are the ministers?
"This is a matter of significant public concern and we have not had anything since Monday from government ministers on the subject, certainly not about the questions now being raised about the links between Hungary and Suffolk.
The H5N1 virus, which causes bird flu, was found on a Hungarian goose farm near Szentes in southern Hungary last month, and thousands of geese were destroyed.
Earlier this month, turkeys were culled at the Bernard Matthews farm at Holton after the virus was found there.
Bernard Matthews has said its products remain safe to eat. Defra also said the risk to human health remained negligible, and properly cooked poultry was safe to eat.