London -

British food retailers must conduct tests on all of their processed beef products, the country's food safety authority ordered on Friday, after frozen beef lasagnas were found to contain 100 percent horse meat.

It is “highly likely” that criminal activity is to blame for the contamination, the Food Standards Agency (FSA) said, without providing details.

The FSA is now demanding that food retailers test beef products such as burgers, meatballs and lasagna for horse meat.

The order comes after the Findus frozen food company found that of its 18 beef lasagna products, 11 contained between 60 and 100 percent horse meat. It has since recalled the products, which it said were made by French food supplier Comigel.

While the horse meat does not pose a health risk, the FSA is ordering tests on the affected lasagna for the veterinary drug phenylbutazone. Animals treated with “bute” are not allowed to enter the food chain.

The unfolding food contamination scandal comes after Irish authorities in January found frozen burger products made by Freeza Meats to contain horse meat. - Sapa-dpa