The full extent of the horsemeat scandal is on a breathtaking scale and may create a danger to public health, MPs will warn today.

Further revelations are predicted by the House of Commons Environment Select Committee which appear to contradict David Cameron's suggestion last week that the crisis is a food labelling issue.

The MPs will say in their report it is impossible that criminals prepared to trade horsemeat as beef are also following hygiene guidelines.

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Last night, an emergency meeting of EU agriculture ministers in Brussels agreed to random DNA testing of processed meat amid continuing fears over the scandal.

It will check for bute, a powerful horse anti-inflammatory drug that is banned from the food chain and has been linked to cancer in humans. The move follows pressure from Environment Secretary Owen Paterson, who wants an EU-wide testing regime.

The Food Standards Agency (FSA) is about to announce the results of tests for bute, which is used in horses killed in UK slaughterhouses. It has so far not been found in any of the contaminated meat sold in supermarkets.

The committee will also raise concerns about the wider health implications of the illegal trade in horsemeat.

Their report includes evidence from the Chartered Institute of Environmental Health, which has warned the shortcomings may endanger health.

The committee's document says: "We agree. It seems improbable that individuals prepared to pass horsemeat off as beef illegally are applying the high hygiene standards rightly required in the food production industry."

Committee member Barry Gardiner, the Glasgow-born Labour MP for Brent North, said: "If people are prepared to lie to you about what's in your food then you can have no confidence they are not putting other stuff in as well. These people are criminals. When there's been a total failure of the food security system you can have no trust in the food."

The MPs said the FSA should be given statutory powers to order retailers to test their products.

Anne McIntosh, the committee's chairwoman, said: "The scale of contamination in the meat supply chain is breathtaking. More revelations will doubtless come to light in the UK, and across the EU. There is every indication that horsemeat has been intentionally substituted for beef by criminals with access to the food industry."

The Prime Minister sampled a pork pie during a Cumbria Day event at Westminster in a scene which echoed former Tory Agriculture Minister John Gummer eating a burger with his daughter at the height of the mad cow disease crisis in the 1990s.

Mr Cameron said anyone passing off horsemeat as beef should face "the full intervention of the law", but insisted there was no evidence that products on sale were unsafe.

On Tuesday, Waitrose withdrew batches of economy frozen meatballs from sale after they were found to contain up to 30% pork content. They were made at the Freshlinks plant in Glasgow. Analysis carried out by ABP, the company which owns Freshlinks, found no traces of pork in the Waitrose meatballs, but tests by the supermarket found 1% pork content in one check and 30% pork content in a second.

ABP stressed it had carried out 450 DNA tests at the Glasgow plant in the past two-and-a-half years.

Scottish food safety inspectors have until tomorrow to report findings from 229 manufacturers, processors, abattoirs and butchers.

Inspectors will take samples of products if there are concerns about provenance and species used in manufacture, with the results being made available to the FSA.