Value beefburgers have been taken off the shelves in national supermarkets Tesco and Iceland after traces of horse meat were found in their products.
Tesco has stores in Falmouth, Helston, Camborne, Redruth, Penzance and Truro, with an 'Extra' superstore in Pool, while Iceland has stores in Falmouth, Camborne, Redruth, Truro and Penzance.
Branches of Lidl and Aldi in the Republic of Ireland were also affected by the contamination.
Traces of horse DNA were found in the burgers after tests by Irish food safety officials two months ago. In one sample of a Tesco value beefburger up to 29% of the product contained horsemeat. The officials said there was no risk to human health.
Tesco said it was "working... to ensure it does not happen again".
The affected meat came from two meat processing plants in Ireland, Liffey Meats and Silvercrest Foods and the Dalepak Hambleton plant in Yorkshire.
Investigations are now underway to find out how the meat became contaminated.
Tesco's group technical director, Tim Smith, stressed the company "immediately withdrew from sale all products from the supplier in question" after receiving the test results on Tuesday.
In a statement, Mr Smith said food safety and quality was "of the highest importance to Tesco" and "the presence of illegal meat in our products is extremely serious".
He added Tesco was "working with the authorities in Ireland and the UK, and with the supplier concerned, to urgently understand how this has happened and how to ensure it does not happen again".
Iceland said it "would be working closely with its suppliers to investigate this issue and to ensure that all Iceland brand products meet the high standards of quality and integrity that we specify and which our customers are entitled to expect".
Aldi is conducting its own internal investigation and Lidl said it had taken the decision to remove the affected products from sale.
"A full investigation is underway to ascertain how this incident occurred," a Lidl spokesperson said.