School meals containing horse meat were served across Bath and North Somerset despite reassurances from its supplier.
Welsh Bros Foods said it was shocked to discover that a batch of beef mince it had delivered to 49 primary schools and 10 early years centres across the county contained 1% horse meat, as initial tests had come back negative.
Two other schools outside the district also received the contaminated product.
The Newport-based company had released a statement in early February to say it had not been caught up in the scandal and promised to continue tests for "reassurance purposes only".
However samples of its products that were submitted for a second round of testing came back positive for the presence of equine DNA.
Alan Haycock, managing director of Welsh Bros Foods, said the company is informing its customers and that trading standards were investigating.
The original statement, which was passed to This Is Bath by a spokesperson for Bath and North Somerset council, said: "Welsh Bros Foods do not purchase or process any horsemeat.
"Burgers are produced from forequarter meat and trims from carcasses purchased from approved licensed abattoirs in the UK.
"Welsh Bros Foods produces all of its burgers in house to its own recipes. Welsh Bros Foods does not procure any burgers from anybody else.
"Welsh Bros Foods has as a matter of precaution and re-assurance already submitted burgers, beef mince and beef trims to a laboratory for testing for the presence of horsemeat DNA. All tests were negative for the presence of horse DNA.
"Welsh Bros Foods will be submitting further samples to be tested for the presence of horse DNA on Monday 11.02.13. This is for reassurance purposes only."
The batch of contaminated beef was distributed in mid-December and all beef mince products from the supplier have been with withdrawn by the council.
School menus were altered so no meals containing beef mince will be served following the discovery.
Bath and North Somerset said it was confident that all meals are now free of all traces of horsemeat and also pointed to advice by the Food Standards Agency, which stresses that there was no evidence of food safety risks from horsemeat.