Waitrose remove beef meatballs containing pork

Waitrose have removed two batches of frozen beef meatballs from shelves after "several tests" revealed they contained traces of pork. Waitrose said:

We have discovered that in two batches of our frozen meatballs produced last summer some of the meatballs may contain some pork. Several tests have been done on this product and, even though the results have been contradictory, we have taken the precautionary action of removing the frozen meatballs from sale and putting up customer information notices in all our branches.

The meatballs are safe to eat but pork is not listed as an ingredient and should not be part of the recipe.