No one'd ever eat anything. Simple economics. Besides, it's illegal.
It's not in the UK. It's just considered taboo to eat here by the majority though is probably available in certain select restaurants.
What is illegal (as it's fraudulent) is passing off one meat type as another ie saying something is beef when in fact it's horsemeat.
On the original story, I seem to remember there was a similar thing around eight years ago with traces of pig dna being found in chicken fillets. The chicken had been 'plumped' in Holland during processing to gain mass and thus profit by injecting some kind of strange cocktail derived from pig slaughter residue, ground up bones and intestines, all hidden in an E number or some similar non descript way.
