MP Keith Vaz has called for a full inquiry following the discovery that a halal lamb burger made by a company supplying schools contained up to 50 per cent pork.
The Leicester East MP said: "I am deeply concerned by the reports meat presented as being halal contained pork and was served in city schools.
"The only right and proper response is any meat due to be served as halal is tested first.
"We need a full inquiry to establish how the companies concerned have been issued halal certificates and to make sure other public services serving halal food are not similarly affected. "
The city council said last week that the halal burger, supplied by Paragon Quality Foods, of Doncaster, had been removed from 19 school menus.
The firm has said it has never knowingly bought or handled pork, but a DNA test carried out on behalf of the city council found the burger contained between 10 and 50 per cent pork.
The burgers had been on Leicester school menus since January and are the only product supplied to the council by the Yorkshire firm.
All other halal products used in council kitchens are supplied by The Punjab Kitchen, of Tyneside.
Tests have shown it is halal compliant.
Further tests on other burger samples are being carried out. Results are expected this week.
