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
The chancellor now faces the prospect of forming a minority government or calling for a snap election.
The 73-year-old said a return is unlikely "given the politicised atmosphere that seems to have afflicted our set."
Chancellor Philip Hammond said the UK will make a financial proposal to the EU in the next three-and-a-half weeks.