^ wot 'e said. Meat for consumption has to undergo vigorous safety checks and has to have total tracability from farm to abbatoir. There are certain vetinary drugs that cannot be used on livestock that is going into the food chain. These checks etc will not have taken place on Tarquin's pony and it is likely to be unsuitable for consumption. Horsemeat reared for the table is a totally different matter, but it is unlikely that what is turning up in Tescos will have been bred for the foodchain.
I agree that this is possible although I would not want to single out any particular company here - the signs so far indicate this situation may have its origins outside the UK. It's difficult to see what the advantage would be in mixing legallly slaughtered horsemeat with beef as the price difference is not that great - it means a huge risk for not much money.
Criminals in food fraud prefer their illegal acts to make a great deal of money. Horsemeat that has come from illegal slaughter or knackers yards has very little value but getting it back in the food chain transforms a worthless carcase into something worth hundreds or thousands of pounds. There have been a number of such cases in the UK over the years, albeit on a smaller scale than this one.
However, such meat can be very dodgy stuff indeed. It may not only have veterinary drug residues but it could come from diseased or fallen stock. Once minced, though, many of the more obvious telltail signs in whole joints and sides (oedema, emaciation, abscesses, muscle congestion and haemorrhages etc.) of such an origin are removed. You may not fall ill if you eat it well-cooked but I wouldn't want it in my food.
The adulterated meat probably came into the UK as a minced product precisely because that helps to mask its origin. Even if it wasn't, it is not easy to tell beef and horse apart (unless you are a butcher experienced in both) without testing as the type of cheap old cow beef that ends up in economy burgers can look similar to horsemeat (both have yellow fat).
Interesting that this is not just a UK problem, with us over-reacting to horsemeat as a foodstuff - watching Euronews, it's causing a crisis in many other countries as well.