A food standards official told lawmakers that burgers sold in British supermarkets could have been contaminated with horse meat for more than a year.
Food Standards Agency chief executive Catherine Brown said that a filler containing beef and horse meat that came from Poland could have been used by the burger processor at the centre of the scandal for at least 12 months, The Sun reported.
Appearing before a committee of MPs, Brown said: "This filler had been used for a year. When the Polish get to the bottom of this, we hope to know whether it's likely this has been going on for all that time."
Brown said there could be prosecutions over the scandal.
Tim Smith, of the Tesco chain told the parliamentary committee that the firm has taken legal advice about the possibility of being sued.
Tesco was rapped over a burger with 29 percent horse meat, The Sun said.
Health Minister Anna Soubry, however, told the MPs: "We don't know whether or not the Irish - the people who made the burgers - didn't themselves know that the meat coming in was in some way contaminated."
"It could be there is a genuine fault in Poland with the supplier of this meat, either deliberately or not, because they haven't been doing the right checks."