Investigations are under way into the presence of horse meat in beef burgers which were being sold in the UK and the Irish Republic.
Irish food safety officials - who carried out checks two months ago - said the products had been stocked by five supermarket chains, including Tesco stores in Britain.
Tesco has apologised to its customers saying what's happened is "very distasteful".
Officials stress that there's no threat to human health.
Patrick Wall, associate professor of public health in University College Dublin, explained to Today presenter John Humphrys that "the burgers wouldn't taste any different if there is a trace" of horse meat in them.
"Consumers are being mislead here and that's why the food agency have taken action," he said.
"If you buy beef burgers you expect to get beef burgers... people who are not actually engaged in ideal practices will be found out."
"This could be the result of a deliberate contamination or it could be inadvertent contamination," he added.
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