Horse meat could have been in beef burgers for years but remained undetected because of insufficient food regulation, it was claimed.

The UK's food watchdog, the Food Standards Agency (FSA), is considering taking legal action against companies at the centre of the scandal.

The FSA said it would consult relevant local authorities and the Food Safety Authority of Ireland (FSAI) over whether to take action against any organisations embroiled in the controversy.

But the organisation was criticised for not carrying out tests in the past because horse meat posed no threat to public health, the Daily Telegraph said.

Tim Lang, a professor of food policy at City University in London told the newspaper: ''It could have been going on for years but we wouldn't know about it because we have never conducted tests.

''For too long we have had light-touch regulation. The Food Standards Agency has to be institutionalised into taking a more critical approach. They have to work on the assumption that things could go wrong.''

After a meeting with food industry representatives, the FSA said it would continue its review of the traceability of the food products identified in an FSAI survey, which uncovered the scandal.

It also said it would try to further understand how the lower levels of horse and pig meat contamination took place and help to carry out a UK-wide study of food authenticity in meat products.

Meanwhile, the food company at the centre of the scandal yesterday vowed to adopt strict DNA testing of its products to prevent a repeat.

The ABP Food Group, one of Europe's biggest suppliers and processors, is being investigated by health and agriculture authorities in the UK and Ireland over the controversy.

Two of its subsidiaries, Silvercrest Foods in Ireland and Dalepak Hambleton in Yorkshire, supplied beef burgers with traces of equine DNA to supermarkets, including one product classed as 29% horse.

An ABP spokesman said: ''It is vital that the integrity of the supply chain is assured and we are committed to restoring consumer confidence.''

A third company, Liffey meats, based in Co Cavan, Ireland, was also found to be supplying products to supermarkets with traces of horse DNA.

Suppliers in the Netherlands and Spain have been identified as the possible sources for incorrectly labelled ingredients.

The results of the FSAI survey, verified in laboratories in Germany, showed low levels of horse in beef products sold in Tesco, Lidl, Aldi, Iceland and Dunnes Stores in Ireland.

Some burgers were also being sold in the UK but retailers insisted all suspect brands had been taken off the shelves within hours of the findings being released yesterday evening.

Prime Minister David Cameron said supermarkets had to take responsibility for what he said was an extremely disturbing case.

''This is a completely unacceptable state of affairs,'' he said.

''It is worth making the point that ultimately retailers have to be responsible for what they sell and where it has come from.''

The FSAI analysed 27 beef burger products with best before dates from last June to March 2014 with 10 of the 27 products - 37% - testing positive for horse DNA and 85% testing positive for pig DNA.

Simon Coveney, Ireland's Agriculture and Food Minister, said the issue should not be seen in the same light as BSE or a dioxin scare in Irish pork meat from four years ago.

''There's no health issue here. But I'm not comfortable eating horse meat like lots of others,'' he said.

''But that's not the issue. The issue is if someone has consumed a burger and something was in that burger that they did not know about. There's no health risk with that.''

Ten million burgers have been taken off shelves as a result of the scandal.

Professor Alan Reilly, head of the FSAI, insisted there is no health risk. He also said that FSAI further tests confirmed that the meats containing horse DNA did not show any traces of medications frequently given to horses.

Despite the clearance over health concerns, authorities, including Prof Reilly and Mr Coveney, warned about reputational damage caused by unacceptable mislabelling for people not eating meat on religious grounds.

The ABP spokesman said it was examining current contracts with its European suppliers.

''We take this matter extremely seriously and apologise for the understandable concern this issue has caused,'' he said.

''ABP Food Group companies have never knowingly bought, handled or supplied equine meat products and we acknowledge the understandable concern created as a result of the Food Safety Authority of Ireland's DNA frozen beef burger test results.''

The only burgers affected were frozen, and fresh products from the companies were not involved.

''We are shocked by the result of these tests, and are currently at a loss to explain why one test showed 29% equine DNA,'' ABP said.

The company said it had sent auditors to two supplier sites on continental Europe for ''unannounced spot checks''.

Results from ABP's own DNA tests are due in several days.

''While extensive and thorough safety checks are conducted on all meat products, the industry does not routinely DNA test meat products. As a result of this incident we are implementing a new testing regime for meat products which will include DNA analysis,'' the company said.

Liffey Meats said it believed horse DNA was originally contained in raw ingredient marked ''bovine only'' and supplied by an EU approved factory.

It said the traces of horse in three of its products were minute.

''Liffey Meats has never produced, purchased or traded any equine products,'' the company said.

''Ingredients were supplied from an EU approved plant and were certified from bovine sources only. We now believe that such imported raw ingredients were the ultimate source of the DNA traces found in some of our products.''

Liffey Meats is also DNA testing all ingredients at its Ballyjamesduff plant.

Concerns have also been raised over the extent of reputational damage to Ireland's food industry, worth nine billion euro (£7.48 billion) last year.

''There is a serious issue here because of that,'' Mr Coveney said.

''The most important issue here is that our systems have worked. They have flagged a problem and we have to deal with that problem and I think we need to deal with that quickly.''

The minister said he was confident buyers of Irish food would not pull the plug on deals.

''It's important to understand that most of the beef and meat product that gets exported out of Ireland is fresh meat,'' he said.

A Defra spokesman said: ''Consumers should have confidence that food is exactly what it says on the label and there are strict rules requiring products to be labelled accurately.

''Defra is working with the Food Standards Agency to urgently investigate how a number of beef products on sale in the UK and Republic of Ireland were found to contain horse and pig meat.

''The investigation will trace the meat back to its source to find the cause of the contamination and any appropriate enforcement action will be taken.''