Pork DNA has been found in Halal chicken sausages that have been served in at least one primary school in London.
Other tests revealed that lean minced beef supplied to Westminster council showed evidence of lamb and pork DNA.
The local authority said it immediately ensured both items were removed from all school menus and had instructed the contractor to temporarily cease supplying meat until the issue was resolved.
The council named the school involved as St Mary’s Bryanston Square, a Church of England school in west London.
The council said it had asked its contractor to no longer use its Halal meat supplier.
The problem came to light after the authority decided to carry out its own proactive tests on food contamination in the wake of the horsemeat scandal.
In a separate development, supermarket chain Aldi said a random sample of its Oakhurst Frozen Meatloaf had been found to contain horsemeat.
An Aldi spokesman said: “Aldi has been contacted by the FSA to alert us that a random sample of our Oakhurst Frozen Meatloaf has been found to contain horsemeat.
“The product is not part of our main range of everyday products and was stocked on a limited availability basis. However, we have immediately withdrawn the remaining stock.”