Tests for the horse painkiller "bute" in Findus food products have come back negative, agriculture minister David Heath has told the House of Commons.
But Mr Heath told MPs that traces of bute, which is potentially harmful to human health, were found in eight horse carcasses from UK abattoirs, three of which have entered the food chain in France.
The minister met representatives of British food retailers and suppliers on Wednesday and received assurances that "meaningful" results will be available on Friday from tests designed to detect the presence of horse meat in products labelled beef.
Mr Heath's announcement followed the publication of a scathing report condemning the Government's "flat-footed" handling of the horse meat scandal, which said its ability to respond had been weakened by cuts to the Food Standards Agency (FSA).
The Commons Environment, Food and Rural Affairs Committee said the public appeared to have been "cynically and systematically duped" for financial gain by elements of the food industry - raising wider concerns about the safety of the contaminated products.
"It seems improbable that individuals prepared to pass horse meat off as beef illegally are applying the high hygiene standards rightly required in the food production industry," it said. "We recommend that the Government and FSA undertake a broader spectrum of testing for products found to have the highest levels of contamination ... to provide assurances that there is no other non-bovine DNA or any other substances that could be harmful to human health present."
The warning came as EU ministers agreed to the random testing of meat products across Europe for the horse anti-inflammatory drug phenylbutazone - or "bute" - as well as for horse DNA.
Chief medical officer Professor Dame Sally Davies said: "Horse meat containing phenylbutazone presents a very low risk to human health. Phenylbutazone, known as bute, is a commonly-used medicine in horses. It is also prescribed to some patients who are suffering from a severe form of arthritis.
"In patients who have been taking phenylbutazone as a medicine, there can be serious side-effects but these are rare. It is extremely unlikely that anyone who has eaten horse meat containing bute will experience one of these side effects."
The FSA said eight out of 206 horse carcasses checked had tested positive for bute. Six, slaughtered by LJ Potter Partners at Stillman's (Somerset) Ltd in Taunton, Somerset, were sent to France and "may have entered the food chain". The remaining two, slaughtered at High Peak Meat Exports Ltd in Nantwich, Cheshire, did not leave the slaughterhouse and have been destroyed.