The Ministry of Justice is to suspend a firm supplying meat to prisons after tests found that it may have provided pies and pasties described as halal – but with traces of pork DNA.
The Food Standards Agency (FSA) said the local authority involved was investigating, while the MoJ said the products have been withdrawn.
Justice minister Jeremy Wright said the incident was “absolutely unacceptable”.
Under Islamic law, Muslims are strictly forbidden to eat pork.
In a statement, Mr Wright said the Prison Service was investigating the incident “as a matter of urgency”.
“This is an absolutely unacceptable situation and one which we regret greatly.
“Clearly this must be distressing for those affected and they can be reassured we are doing everything we can to resolve the situation.”
Steve Wearne, an FSA director, said it had called an urgent meeting “of a range of suppliers” on Monday where it would “stress again the responsibility of all food businesses to ensure the food that they sell contains what it says on the label”.