Opposition MPs are demanding tighter food labelling rules after Irish pork products were contaminated with potentially harmful level of dioxins.

Thousands of food items containing Irish pork were withdrawn from supermarket shelves across the UK this week following the discovery of dioxin levels up to 200 times the legal limit in pig feed used on 47 farms in the Irish Republic.

But Tory shadow farm minister Jim Paice suggested some products containing Irish pigmeat may still be on sale. Current laws meant meat from pigs reared in Ireland and processed in the UK could be labelled British, he said.

“For years, the government has resisted attempts to require clear country of origin labelling, accepting that the consumer is often deceived. We now have potential health risks as a result of this deception.

“Sausages, pies or bacon labelled as British may well contain contaminated Irish pigmeat but even a consumer who hears the warning may look in the fridge and wrongly decide that as it is labelled British there is no risk.”

Dioxins are formed during waste incineration and during some industrial processes. They are normally found in low levels but some are highly toxic and can cause cancer and damage to reproductive and immune systems.

Suspicions of contamination were first raised earlier thus month when a routine test on a batch of pigs indicated a presence of polychlorinated biphenyls (PCBs) – banned in the Irish Republic since the 1970s – in their animal feed.

Lib Dem shadow DEFRA secretary Tim Farron has tabled an Early Day Motion in the House of Commons calling for stricter labelling standards of processed meat. The recall showed how a quickly a problem on only a few farms could spread, he said.

“We now have much clearer rules which require supermarkets to label the origin of fresh meat on its packaging. But for processed meat products such as pizzas, toad-in-holes, and pasties the same rules are much harder to enforce.

“In the wake of the Irish pork recall, it’s important that the government continues to seek stricter laws regulating the labelling the meat. If they do so, both British farmers and consumers will benefit.”

Millstream Power Recycling of County Carlow, which recycles food into pig meal, is thought to be responsible for the food scare. Officials are testing oil from a machine used to dry animal feed and the company is carrying out a full investigation.

Irish Farmers’ Association president Padraig Walshe said the contamination was a huge blow to Irish farming. He added: “The animals on those farms will probably be disposed of but those farms have been isolated since the middle of last week.”

The Food Standards Agency (FSA) said it was advising consumers not to eat pork or pork products, such as sausages, bacon, salami and ham, which are labelled as being from the Irish Republic or Northern Ireland.

It added: “We do not believe there is significant risk to UK consumers. Adverse health effects from eating the affected products are only likely if people are exposed to relatively high levels of this contaminant for long periods.”