Ministers are facing calls to impose a ban on meat imports from the European Union amid concerns that the extent of the contamination of the British food chain is still not fully understood.

The Environment Secretary, Owen Paterson, has been criticised for his confused handling of the horse-meat scandal after he ruled out an import ban despite conceding that tainted foods could be "injurious to human health".

Mr Paterson is going to have to address the Commons in a high-pressure performance today as his department's public relations strategy appeared to be in disarray. The Minister's own Department for Environment, Food and Rural Affairs (Defra) sought to clarify its position last night and play down concerns that the horse meat scandal could pose a health risk. A Defra spokesman said: "There is currently no evidence of a risk to human health. Owen Paterson was quite clear that while we must be prepared to find more evidence of fraud, there is not a food safety risk at present. The FSA has said that unless there is advice to avoid a specific product, there is no reason for people to change their shopping habits.

"The Government and the FSA are working with authorities across Europe, including police, to get to the bottom of this unacceptable situation. If criminal activity is discovered we will take whatever action is necessary."

Mr Paterson, who is understood to have received a dressing down from Downing Street over a lethargic initial reaction to the presence of horse meat in processed food, has warned of more "bad results" this week from further tests by retailers.

A senior Conservative MP called for a moratorium on EU meat imports until the investigation into the origins of the horse meat - which yesterday switched focus to Romania amid suggestions of links to organised crime - could be established. Mr Paterson said no such ban could be considered under EU law until a risk to human health had been identified - only to admit that such a risk could take several more days to uncover.

The Independent has established that only beef products which have already been found to contain horse meat and withdrawn from sale by companies including Findus and Aldi are currently being tested for phenylbutazone or "bute", a veterinary drug which is banned from the human food chain.

Speaking to LBC Radio, Mr Paterson insisted there was currently "no evidence" of a health risk. He said: "As we speak this is an issue of fraud and a conspiracy against the public, I think probably by criminal elements to substitute a cheap material for that which was marked on the label.

"It is a labelling issue. Now we may find out as the week progresses and the tests begin to come in, we may find out there is a substance which is injurious to human health. We have no evidence of that at all at the moment."

The Food Standards Agency has asked retailers and local authorities to provide results by this Friday from tests for horse meat contamination on dozens of processed beef products. Further analysis for bute, which can take a minimum of 48 hours, will be carried out only if horse meat has been found, meaning it could potentially be another week before any human health risk is established. Tests for bute on Findus beef lasagne and similar products from Aldi, both which have been withdrawn after they were found to consist of up to 100 per cent horse meat, are under way.

Anne McIntosh MP, the chairwoman of the House of Commons Food and Rural Affairs Select Committee, 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."

Why the long face: muddling minister

* It took 36 hours after news broke that "100 per cent horse meat" ready meals had been found on sale in the UK before the Environment Secretary Owen Paterson felt able to take to the airwaves to explain what the Government was doing. Even then it was five hours after Downing Street promised he would appear.

* Mr Paterson yesterday raised the potential for horse meat to have been contaminated by phenylbutazone. In significant doses, it can produce a potentially fatal blood condition. But nutritionists point out that a greater risk is likely to come from the high levels of salt and fat in processed meals.

* Despite pledging to provide a co-ordinated response to the scandal, Mr Paterson's department failed to invite frozen foods giant Findus to an industry "horse meat summit" this weekend. He was forced to deny yesterday that caterers supplying schools and hospitals had also been excluded.