A halal lamb burger made by a company supplying Leicester schools contained up to 50% pork, the city council has confirmed.
The products were made by Doncaster-based Paragon Quality Foods Limited, which said it had never knowingly bought or handled pork.
The discovery was made on 18 April and the product was withdrawn but details only became public on Thursday.
A DNA test found the burger contained between 10 and 50% pork.
‘Criminal procedure’
A spokeswoman for Leicester City Council said: “Because it was only one burger that was tested and the findings were so wide-ranging, we have ordered further samples of more burgers and when we have these results we will publish them.
“The council’s view is that whether it’s 1% or 99%, it’s still impure and unacceptable.”
The horsemeat scandal prompted the council to test all meat served in its schools and one burger was taken as a sample.
The lamb burgers were served at 19 schools around Leicester but were withdrawn as soon as the discovery was made.
The revelation prompted outrage among parents and the city’s Muslim community.
Suleman Nagdi, from the Federation of Muslim Organisations, said: “For people, this is touching at the very tenet of their faith, the very heart of their faith.
“There needs to be a criminal procedure against the company,” he said. “At least it would bring some confidence into the community.”
Faz Mulla, from the not-for-profit Halal Monitoring Committee, was at a meeting of imams on Thursday.
“What transpired is the total loss of confidence in the supply chain in Leicester. Imams are at a loss as to what to do about this matter,” he said.
A vote was taken by the imams calling for halal meat to be taken off the menu, and for children to become vegetarian until confidence is restored.