The tests covered a range of frozen, chilled or canned products that included lasagne, chilli con carne, cottage pie, ravioli, cannelloni and spaghetti bolognese.
The three products confirmed to contain levels of pig DNA are Asda's spaghetti and meatballs and beef cannelloni and a beef lasagne from local authority supplier Apetito.
Spanish authorities, meanwhile, announced that traces of horse meat were found in a beef cannelloni product by one of the brands of Nestle, a Switzerland-based food giant.