A study carried out by the Food Services Agency found that injection powders used to retain water in chicken breast products could contain hydrolyzed beef and pork proteins.
In the samples examined, the agents used to hold added water in the breast contain salt, phosphates and hydrolyzed animal proteins, which were found to be beef and pork instead of chicken.
If water content is higher than 5%, it must be declared in the name of the food and listed as ingredient, FSA recommends.
FSA says there is no evidence to suggest a widespread problem with undeclared products but insists that consumers should be aware of what they are eating.