First of all, correct me if I'm wrong someone but I pretty much have never heard of someone being allergic to one type of meat and not another. I mean sure; people being allergic to fish or people being allergic to poultry but being able to eat red meat I could get. Yet that is not the same as being allergic to a certain type of red meat when not allergic to other red meat types.
I guess you could be referring more to perhaps something to do with feed, Tara? Or chemicals present in the meat? Again I may be wrong but cooking meat until properly cooked in an oven at around 200 degrees celcius would destroy the chemicals in it. It's kind of why we cook most meat instead of just eating it raw. Diet wise, I'm fairly certain the average horse is fed better than the average pig. We don't hear people (non muslims at least) complaining about pork or the diet the pig has before it is slaughtered which can include the offal.
The fact that people find it wrong to eat one type of animal and not another is quite amusing, how is eating horse meat more disgusting or wrong than eating lamb, pork or beef? I can understand, why you wouldn't eat endangered species or animals with a toxic flesh to us but we aren't talking bout an animal in either of those categories, we're talking about an animal that for almost the entirety of human history has been farmed, bred and used for everything from transport and war to food. It's not like this is something new and unusual even within the realms of British History, in fact it's probably only in the past 100 - 150 years that the consumption of horses in the UK has become something uncommon or even disapproved of. Why was this? I don't have the answer I certainly don't agree with it on principle of if a pig is good enough to eat, why not a horse? Why not a dog or a cat? Certainly scientists seem to believe that the growing population of Earth will see us eating a diet with more insects and diversified meat sources in. When you consider what animals are easily raised, farmed and kept? I can easily see those "diversified meat sources" being dogs, cats, rodents of various forms.
The law however has been broken and I agree this is wrong. Our laws since at least the 1970s have been there to protect innocent consumers from being mis-informed and unfortunately in this situation we've all been duped. However this is something which can easily be resolved by forcing food production companies to do one of two things: Only use approved beef (maybe harder to achieve than state since it appears the food companies in some instances were duped by vets being paid off/intimidated in to approving the meat as beef) or to remove the term beef from their packaging substituting it for meat instead. I know "Findus meat crispy pancakes" does not have the same impact in advertising as "Findus beef crispy pancakes" but as I've outlined previously; I don't agree that the eating of horse meat is harmful in any way, shape or form. I certainly believe that most of the crap we see in the papers is your usual Daily Mail fear-mongering bulltrout we see every day about video games, the internet and so forth it's sensationalized and designed to do nothing more than sell papers.