Cottage pie delivered to schools in Lancashire has tested positive for horse DNA.
The product, which has been delivered to 47 schools, has now been withdrawn.
Headteachers are said to have been told.
Scientists uncovered provisional tests which showed the horse DNA late yesterday afternoon at one of the county’s testing labs, used in the investigation by the Food Standards Agency.
County Coun Susie Charles, cabinet member for children and schools, said: “We share the concerns people have about what is clearly a major problem in food supplies across the UK and Europe.
“Because of those concerns we decided to seek extra assurance that our external suppliers were not providing any products containing horsemeat DNA, and one of the products has returned a positive result.
“Relatively few schools in Lancashire use this particular product but our priority is to provide absolute assurance that meals contain what the label says – having discovered this one doesn’t, we have no hesitation in removing it from menus.
“This does not appear to be a food safety issue but I’ve no doubt parents will agree we need to take a very firm line with suppliers and it is a credit to our officers that we have been able to quickly identify the problem and take the product off the menus.”