Environment Secretary Owen Paterson will update MPs on the horse meat scandal after warning that the next set of tests could produce more bad results.
Mr Paterson's Department for Environment, Food and Rural Affairs (Defra) has sought to play down any concerns that the scandal could pose a health risk and said there is "no reason for people to change their shopping habits".
But there are fears that the full scale of the scandal has yet to emerge. The Environment Secretary said the Government was powerless to impose a ban on meat imports unless beef contaminated with horse meat is found to be a health risk.
Mr Paterson spoke after the chair of the Environment, Food and Rural Affairs Select Committee backed a ban on meat imports and urged the public to buy their meat locally.
Conservative MP Anne McIntosh said: "I believe there should be a moratorium on the movement of all meat until such time as we can trace the source of contamination." But shadow environment secretary Mary Creagh said banning meat imports was a "knee-jerk reaction".
The Food Standards Agency (FSA) has said there is no evidence to suggest the horse meat detected in beef products poses a danger to humans, but confirmed that tests have been ordered for the veterinary drug phenylbutazone as animals treated with "bute" are not allowed to enter the food chain.
Frozen foods firm Findus, which has taken its beef lasagnes made by French food supplier Comigel off shelves after some were found to have up to 100% horse meat in them, said it was considering taking legal action against its suppliers as an internal investigation "strongly suggests" that the contamination "was not accidental".
Mr Paterson said no case for criminal action has been discovered in the UK yet but the FSA said it was "working closely" with police in case that changes.
The scandal has spread all over the continent as details of the elaborate supply chain in the meat industry emerge. French consumer safety authorities have said companies from Romania, Cyprus and the Netherlands as well as its own firms were involved.
Romanian authorities have confirmed they are investigating. One theory for the apparent increase in the presence of horse meat in the food chain is new restrictions on using horses on roads in Romania, which have led to a surge in numbers of animals being put down.