The Food Safety Authority has found traces of horse DNA in burgers made at plants in the UK - including Dalepak in Hambleton, North Yorkshire.
The meat also came from two processing plants in Ireland - Liffey Meats and Silvercrest Foods.
The burgers were on sale in Tesco, Dunnes Stores, Lidl, Aldi and Iceland.
A total of 27 products were analysed, with ten of them containing horse DNA, while 23 of them tested positive for pig DNA.
Horse meat accounted for approximately 29 per cent of the meat content in one sample from Tesco.
The FSA said the findings do not pose a risk to public health.
However, it said that it raises concerns about the traceability of meat ingredients.