Katherine Brown, chief executive of the Food Standards Agency, told MPs that the Polish supplier at the heart of the scandal has been selling beef “filler” to an Irish meat processor for over a year.
Anne McIntosh, the chairman of the committee, said: “How do we know that this horse meat has not been in beef burgers for months if not years?”
Mrs Brown said: “It is possible that these burgers have been on sale in this country for a year. This filler had been used for a year. And therefore when the Polish get to the bottom of this we will hope to know whether it’s likely that this has been going on for a year.”
Mrs Brown told MPs that the FSA had not identifies horse meat as a risk in the past, which is why it was not tested for.
But they hope that investigations in Ireland and Poland will get to the bottom of the situation.
Meat from a plant in Ireland was supplied to food companies including Tesco, which withdrew from sale all products supplied by Silvercrest in County Monaghan.
The Irish Minister for Agriculture, Food and the Marine Simon Coveney announced earlier this week that their tests had shown that the horsemeat was probably being imported from Poland.
The result showed “significant levels” of equine DNA in imported “raw material,” amounting to 20 per cent horse DNA content relative to beef.