The contaminated burgers were made by the Irish-based processing company, Silvercrest, which is part the ABP Foods Group.

The same company also made tainted burgers for Tesco, Asda and the Co-op, among others.

Burger King has faced allegations of orchestrating a cover-up of its links to the horsemeat scandal in order to give it time to find an alternative supplier.

It is currently shipping in tens of thousands of burgers from suppliers in Germany and Italy in order to meet demand at its UK outlets.

It is known that the management at Silvercrest has been using a series of non-approved ingredients in their burgers for a range of household name brands.

These included meat off-cuts, including horse, that were imported in large frozen blocks from Poland.

The contamination has been going on since at least last May and potentially for up to one year, according to evidence presented to MPs earlier this week.

Tonight Burger King abandoned its earlier denials, saying: ‘Four samples recently taken from the Silvercrest plant have shown the presence of very small trace levels of equine DNA.

‘Within the last 36 hours, we have established that Silvercrest used a small percentage of beef imported from a non-approved supplier in Poland.

‘They promised to deliver 100per cent British & Irish beef patties and have not done so. This is a clear violation of our specifications, and we have terminated our relationship with them. 

‘Through our investigation, we have confirmed that this non-approved Polish supplier is the same company identified by the Irish Department of Agriculture as the source of Silvercrest’s contamination issue.’

The contamination scandal was first triggered two weeks ago, with the Food Safety Authority of Ireland revealed it had found horse meat in burgers sold in Ireland and the UK.

When the news first emerged, Burger King said it had been given an ‘absolute assurance’ by its supplier that its products were not involved.

Yesterday, Burger King vice president, Diego Beamonte, said: ‘We are deeply troubled by the findings of our investigation and apologise to our guests, who trust us to source only the highest quality 100per cent beef burgers.

‘Our supplier has failed us and in turn we have failed you. We are committed to ensuring that this does not happen again.’

He added: ‘We will dedicate ourselves to determining what lessons can be learned and what additional measures, including DNA testing and enhanced traceability controls, can be taken to ensure that we continue to provide you with the quality products you expect from us.’

Jeanette Longfield, of the campaigning food and health group, Sustain, has condemned Burger King’s handling of the problem.

‘Burger King’s approach has been very shabby,’ she said.

‘It really is not the open, honest and transparent way that we expect a major food company to treats its customers.’

Earlier today, Aldi admitted for the first time that burgers sold through its UK stores were also probably contaminated with traces of horse meat.

Its burgers were made by a British supplier, Dalepak, which is based in Richmond, north Yorkshire.

The same company manufactures burgers for Iceland, which has also admitted to finding horse meat in products sold to families in this country.

Dalepak also makes burgers for Waitrose and Sainsbury’s, which both insist that their burgers are clear of contamination.

The processing company is a subsidiary of the Irish company, ABP Food Group, which also owns a second burger manufacturing business, which is Silvercrest, in southern Ireland.

Aldi said a sample of its frozen Oakhurst Beefburgers showed up positive for 0.1per cent horse DNA, while its Oakhurst Beef Quarter Pounders were 0.1per cent equine and 0.1per cent pork.

The company withdrew all of its frozen burgers from UK stores when the scandal first erupted two weeks ago as a precaution.

A spokesman said: ‘Customers are our absolute priority. This is why we immediately withdrew these products until such a time that we could verify that there was no risk to our customers.

‘We are deeply angry and feel let down by our supplier and we are pursuing more tests until we are certain that we understand how the production line was contaminated.

‘Aldi requires rigorous verification and quality control procedures and we cannot allow our quality commitment to our customers to be compromised.

‘We will continue to maintain active scrutiny across our supply lines, and we assure our customers their health and safety is our number one priority.’