Police in the Irish Republic have been called in to investigate how pigs in the country came to be contaminated with potentially harmful dioxins.
The source is thought to have been feed tainted with oil from a Co Carlow firm which recycles food into pig meal.
Millstream Power Recycling Ltd said it was investigating how the firm's "strict health and safety procedures... could possibly have been breached".
The risk is said to be low, but people are advised not to eat any Irish pork.
The advice also currently includes pork products from Northern Ireland as nine farms there - in addition to 47 in the Irish Republic - were supplied with the same feed being linked to the contamination.
The Irish Republic's chief vet believes contaminated pork products may have been exported to up to 25 countries.
The UK's Food Standards Agency (FSA) said: "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."
The British Retail Consortium said supermarkets across England, Scotland and Wales had withdrawn from sale "the very small proportion" of Irish pork they had in stock, following advice from the FSA.
Similar action has been taken in Northern Ireland.
Suspicions of possible contamination were first raised last Monday as a result of the routine testing of pigs, which indicated the presence of polychlorinated biphenyls (PCBs) - banned in the Irish Republic since the 1970s - in animal feed.
Tests on the slaughtered pigs showed some pork products contained up to 200 times more dioxins than the recognised safety limit.
The chief executive of the Food Safety Authority of Ireland, Alan Reilly, said investigations were ongoing into how the contamination got in to the feed.
Mr Reilly added that culling of animals was likely in order to remove them from the food chain.
He said: "It's more than likely from the types of dioxins that we have that it looks like some kind of industrial oil or industrial contaminant and we're trying to find out where that came from."
The Irish Agriculture Minister Brendan Smith said the investigation involved Irish police.
A spokesman for Millstream Power Recycling said the oil which officials were testing had never been added as an ingredient but was used in a machine used to dry animal feed.
'Very low risk'
He said production at the plant, which is owned by a Robert Hogg and employs around 15 people, was stopped earlier this week when it was first linked to the scare.
He added: "The management and staff at this company have always prided itself on exceeding the strict standards of quality and safety in all aspects of its production.
"Millstream will be carrying out a full investigation to establish how the company's strict health and safety procedures and the high quality standards could possibly have been breached.
"In the meantime, Millstream will continue to work with the Department of Agriculture and Food to ensure that any product sold to the pig industry in recent weeks is identified and recalled."
Dioxins are formed during combustion processes, such as waste incineration, and during some industrial processes.
Chronic long-term exposure to dioxins can have serious health effects, including causing cancers, but food safety expert Professor Hugh Pennington told the BBC the health risk was "very, very low".
He said: "You have to have a lot of these compounds. You have to eat a lot of them, enormous amounts to have any visible effect."
And Ireland's chief medical officer, Dr Tony Holohan, said anyone who had eaten pig meat did not need to seek medical help.
But as a precaution consumers have been warned not to eat any Irish pork and bacon products bought since 1 September.
Bacon, ham, sausages, white pudding and pizzas with ham toppings are included in the recall.