For weeks (years, really, it's a cyclical thing) there's been talk, misrepresentation, misunderstanding, confusion, accusation, and so on, about what 'Halal' is. There are details on numerous Islamic websites by numerous scholars, but they're either unknown (most likely) or ignored (I don't think this is a wilful thing for the most part, as the quest for answers is, for most people, a genuine one).
As always, the likelihood of something I post making a difference or bringing understanding to someone is minuscule, but I'm going to give it a shot - can't hurt, right?
So what is 'Halal' and why has it been kicking up a storm?
Basically it means 'permitted' or 'allowed' or 'pure' - depending on the context in which it is used (I'll try to detail this more fully as I go on, but if a non-Muslim is reading this (I hope there are a few who are!) then one thing you need to bear in mind is that Islam is 'a way of life', and there are rules, guidance, and suggestion for every aspect.)
The opposite of 'Halal' is 'Haram' - things that are 'not permitted', 'not allowed', 'impure'.
Let's start on the food side of things.
Halal isn't about slaughter - that is Zabihah (the word literally means 'slaughtered') - and animals such as sheep and goats are halal for a Muslim to raise and handle, whereas a pig is not. So before it is slaughtered a chicken, lamb, goat, cow etc is halal - it is a pure animal (we'll ignore the whole 'feeding it things that are contrary to what it should be eating' side of things). Regardless of how a pig is slaughtered it can never be considered halal for a Muslim to eat (the extreme circumstance of there being literally nothing else to eat, is just that: extreme. It's unlikely to happen. The other example of being force-fed does not place responsibility on the one being force-fed, so doesn't count, either).
So, again, Halal isn't about the method of slaughter. The method used, however, determines whether the slaughtered animal/poultry can still be considered halal.
Snapping a chicken's neck is not permitted.
Suffocating a chicken is not permitted (but it's done in some poultry farms in the UK (anyone remember Jamie Oliver's piece on this a few years ago?) and has been approved by the FDA in the US).
Electrocuting a chicken to death is not permitted (but, again, is done (usually inadvertently) in some poultry farms in the UK.
Suffocating an animal to death is not permitted (and it's not legal in the UK (yet), either (although that's changing/changed with regards to poultry)).
Electrocuting an animal to death is not permitted (and it's not legal, either, but it is known to happen).
Shooting an animal with a bolt is not permitted (but is legal)
Shooting an animal in the head with a gun is not permitted (but is legal)
The above are the main ways an animal is prepared for slaughter: either rendered unconscious with gas (CO2 or an inert gas), electrocuted unconscious, or shot in the head (and either rendered unconscious or killed).
In the UK the norm in all slaughter (other than Jewish/Kosher and around 10-15% of Halal slaughter) is to stun the animal unconscious and then proceeding with the slaughter.
Here's where one of the complaints kicks in: 'we don't want non-stunned animals for our meat'. You have more chance of there being horse meat in your mince than you have of having a non-stunned animal's meat in your mince. Why? Because of the odds of you eating Kosher or non-stunned Halal meat is pretty much zero unless you're frequenting certain places (although, I understand that certain parts of the carcass from Kosher slaughter is often either passed off as Halal or sold off to the regular chains, so if you do end up (inadvertently) eating meat of a non-stunned animal, it's likely from a Kosher source rather a Halal one). Pizza Express, KFC, GBK etc are not one of those places. In each of those places the chicken you would be eating would have been stunned and then slaughtered.
The other complaint is that of 'I don't want to be eating something that's been blessed for something I don't believe in'. Okay (ignoring the fact you don't believe it, so it shouldn't really harm you), for Christians one of the things you need to keep in mind is that Paul (in his interpretation of Jesus' (as) words) made it clear that it didn't matter what you ate because what goes in isn't what counts, it's what comes out of your mouth you need to pay attention to.
(For Muslims, we have a 'you are what you eat' thing - eat or drink impure things and they will become part of your body and so render you impure)
The third issue is: 'we didn't know and it's not right that we didn't know'. Here I totally agree with you, but one thing you need to bear in mind is that most of the Muslims in the UK didn't know, either. Think about it: if Muslims knew (and believed) that the (regular) lamb being sold in Tescos was halal would they bother going to their local halal butcher?
Which foods are Halal and Haram (in the UK)?
Baked Beans are Halal - the delicious tomato sauce, the whole suitable for vegetarians thing...delightfully halal
Baked Beans and Sausage are Haram
Cucumbers are Halal
So are tomatoes, peas, kidney beans, squash, pumpkin, mushrooms, onions - all Halal
Battered cod is Halal
Beer battered cod, though, isn't :(
Fries, chips, onion rings (fried in veggie oil etc) are all Halal
Fries, chips, onion rings fried in animal fats are not - and they're not suitable for vegetarians, either
Ketchup is Halal
Cheese made without using enzymes from animals are Halal (and suitable for vegetarians)
Cheese made with using enzymes from animals are Haram (and not suitable for vegetarians)
Veggie quiches are Halal
Quiche Lorraine is not (and it's not suitable for vegetarians, either)
Walkers' Cheese and Onion Crisps are suitable for vegetarians (and Halal)
Pringles Original, Sour Cream etc are either vegan or vegetarian (and Halal)
Vinegar is Halal
Clean water is Halal.
All those things listed above as Halal were not deliberately made Halal by their manufacturers as some weird way of getting one up on non-Muslims and drawing in Muslims. They're just 'halal' by their very nature. It's not a conspiracy against non-Muslims.
Moving on from the food side, there are other aspects:
Leather - Muslims (and Jews, and Jains (who won't wear any leather derived from any animal)) won't wear leather made from pigskin. (as an aside, apparently a lot of leather-bound Bibles are bound in pigskin leather, but I haven't researched this, hence the 'apparently'). The method of slaughter 'doesn't matter' as the tanning process is considered to change the nature of the skin and render what was impure (if slaughtered in a way not permitted) into something pure.
Other things that are Halal and Haram
Holding your wife's hand: Halal
Holding someone else's wife's hand: Haram (exception, of course, where you're helping them up etc)
Buying, drinking, selling alcohol: Haram
Anyway, I'll leave it there, but I hope this has been of some help to some people. Apologies for some of the rambling parts.