Irish authorities believe that "filler product" found in contaminated burgers came from Poland and was a mixture of beef and horse offcuts, the Food Standards Agency (FSA) has said.
The contaminated beef, which was sold in supermarkets, was in the form of blocks of frozen product from a Polish supplier that had been used for a year.
Investigations are going on into how long contaminated meat might have been in use, FSA chief executive Catherine Brown told the Commons Environment Committee.
More top news
A Bolton chemistry teacher is to be sentenced today after admitting terror offences - with police claiming he wanted to join Islamic State.
Average household incomes have returned to around the levels they were at before the financial crisis hit, new analysis indicates.
Figures uncovered by a Freedom of Information request reveal one university leader received £623,000 in 2013/14.