As retailers, processors and local authorities embark on a widespread testing regime of processed meat products, the government has warned yet more horse meat could be discovered in food on sale in the UK.

Defra secretary of state Owen Paterson convened an emergency meeting with retailers and processors on Saturday (9 February) to discuss the industry’s response to the scandal, which has widened from frozen burgers to ready meals in recent days and is now affecting a growing number of countries across the EU.

The Food Standards Agency has asked the industry to carry out urgent tests for horse meat on all processed beef products, with the first results to be submitted by Friday (14 February). With widespread testing under way, it was possible more “bad results” would surface, Paterson warned.

He added that, although gross incompetence remained a possible explanation for the scandal, he was increasingly concerned an “international criminal conspiracy” could be behind the adulteration. “This is a straight fraud,” he said. “If a product says it’s beef and actually you are buying horse, that is a fraud.”

The FSA has had discussions with the police but there is no active UK police investigation into the scandal at the moment.

Saturday’s meeting was called after it emerged last week that the meat content of Findus frozen beef lasagne contained large amounts of horse meat, with some products being made with 100% horse instead of beef. The product was supplied to Findus by French manufacturer Comigel, which in turn used a number of sub-contractors to source ingredients from across the EU. Findus has since said it believes it was the victim of fraud, and is planning to take legal action in a French court on Monday.

The FSA has advised all retailers and suppliers that use Comigel to withdraw products on a precautionary basis.

Tesco withdrew its frozen Everyday Value Spaghetti Bolognese last week, and Aldi took its Today’s Special Frozen Beef Lasagne and Today’s Special Frozen Spaghetti Bolognese off shelves. Tests results on the Aldi products have since confirmed their meat content was between 30% and 100% horse meat.

The undeclared presence of horse in food products has also raised concerns about the possible presence of bute – a widely used veterinary medicine which can, in rare cases, be harmful to human health and is therefore not allowed in the food chain.

The FSA has ordered tests for bute on products found to contain horse meat; to date, none have tested positive. However, it is advising consumers not to eat any of the products that have been withdrawn, pending further test results.