Last year retailers and food manufacturers across Europe were caught up in a scandal after it emerged that various meat products contained horsemeat and other undeclared meats.

British supermarket chain Tesco was among the companies whose products were affected and it became the first retailer to introduce DNA testing on its meat products following the scandal.

Now that testing has revealed the presence of undeclared chicken, turkey or lamb in other products.

Tesco said that its Butcher's Choice Sausages, made by Tulip, were found to contain low levels of either chicken or turkey. This was due to different sausage varieties being produced on the same equipment on the same day.

Venison burgers produced by Two Sisters were found to contain between 5 percent and 30 percent lamb, and an investigation of the production site pointed to human error as the cause.

In addition, the testing revealed traces of chicken in Billy Bear turkey and pork sausage slices, made by Feldhues.

A spokeswoman for Tesco said that the discovery of the meat showed that its DNA testing was effective.

"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," she added.

Pork producer Tulip said in a separate statement that the company had launched a thorough review of all aspects of its manufacturing processes. It has also introduced a more stringent hygiene regime and sign-off process, together with staff retraining.