Tesco's DNA testing, which it initiated to tackle issues such as those that caused the horsemeat scandal, revealed undeclared chicken and turkey in pork sausages, and unlabelled lamb in venison burgers. The testing also revealed chicken detected in the branded product Billy Bear, produced by Feldhues.
The latest meat contamination scandal comes as the retail giant is still reeling after it emerged it had been inflating its own profits.
Tesco has admitted it has found contaminated meat and a spokesperson said: "Our world-class traceability and DNA testing system has recently highlighted three incidents where suppliers' products have failed to meet our standards. They indicate the presence of chicken, turkey or lamb where it should not be present. Investigations into each incident have concluded that production line error was responsible and we have worked with suppliers to ensure their controls are effective and our stringent standards are met every time."
On its website, Tesco gave an explanation of how the mistakes had happened: "We found that a batch of Butcher's Choice Sausages (Beef, Pork & Onion and Turkey) contained low levels (between 1-5%) of either chicken or turkey, due to different sausage varieties being produced on the same equipment on the same day.
"Tests also found venison burgers, produced by 2 Sisters, contained lamb (between 5-30%). That prompted a detailed investigation of the production site, which pointed to human error and further improvements 2 Sisters will make to the production process."
The contaminated sausages were made by Tulip. A spokesperson from Tulip said it had already taken steps in response: "Tulip was very disappointed to have fallen below its own high-quality standards in relation to the production of Butcher's Choice sausages. However, the business is now confident that the issues identified have been fully addressed.
"As soon as the results of the testing were confirmed Tulip launched a thorough review of all aspects of its manufacturing processes at the Bromborough site. A more stringent hygiene regime and sign-off process have now been introduced, supported by the instigation of a comprehensive programme of employee re-training."
Stephen Rossides, director of the British Meat Processors Association (BMPA), said: "While this incident poses no food safety risks, it represents a breach of labelling rules and, therefore, has resulted in incorrect information being given to consumers. The precise circumstances of the mislabelling are unclear at this stage, but this incident underlines yet again the need for vigilance and robust procedures in sourcing, raw material controls, manufacturing, and labelling of meat products to ensure that a product is what is says it is."