The investigation into the horsemeat scandal is taking too long and has so far failed to bring any prosecutions, a group of MPs have warned.
The Commons Environment, Food and Rural Affairs Committee expressed "surprise" that in EU-mandated tests, 14 out of 836 samples of horsemeat from the UK tested positive for the painkiller bute - the highest number of positive tests in the EU.
It also said the authorities in both the UK and Ireland - where horse DNA was first discovered in processed beef products - had yet to acknowledge the scale of the illegal activity involved.
The committee called for assurances that the authorities will act if evidence is uncovered to support criminal prosecutions.
"The evidence we received from retailers and food processors in the UK and Ireland suggests a complex, highly organised network of companies trading in and mislabelling frozen and processed meat or meat products in a way that fails to meet specifications and that is fraudulent and illegal," it said.
"We are concerned at the failure of authorities in both the UK and Ireland to acknowledge the extent of this and to bring prosecutions.
"We are dismayed at the slow pace of investigations and would like assurance that prosecutions will be mounted where there is evidence of fraud or other illegal activity."
The MPs acknowledged that horsemeat contamination was limited to a "relatively small" number of beef products sold in the UK, with 99% of products tested containing no horse DNA.
Across the EU as a whole, 4.66% of products tested were found to contain more than 1% horse DNA.
The committee complained that there was still a "lack of clarity" within Whitehall over where responsibility lay for dealing with such issues, and it said the Food Standards Authority was to be an effective regulator.
The committee said there were clearly "many loopholes" in the current system of horse passports and called for assurances that horse movements within the UK and between the UK and Ireland were being properly monitored.
A Defra spokesman said: "It is absolutely wrong for any businesses to con the public by allowing horsemeat to be labelled 'beef'. That's why we have set up an independent review to identify any weaknesses in the food supply chain or the regulatory system to prevent this happening again."
"The police are investigating how products containing horsemeat came to be on sale in the UK and they will take action where any unlawful activity has taken place."