Ok i think people are really getting confused about this
The meat sold in the supermarkets, has had a prayer read as the animal is killed and has had the throat slit and blood drained. The animal will have been stunned prior to this.
There is halal meat available that has not been stunned, but this is by far the minority of halal meat. If as a muslim you wished to buy it you are limited to 2/3 butchers where there are 10/12 in a town. Supermarkets which stock pre packed halal meat in special sections only provide stunned halal meat.
Places like Ikea, KFC and apparently now waitrose buy halal meat, not to appease their muslim customers and do not market their products as halal and in the case of KFC the batter put on the chicken contains non halal (haram) ingrediants, but for market reasons.
If people are upset about the method of slaughter, as the animals are stunned there is minimal difference. If they are upset about the prayer, i think this is fairly foolish as when buying mass produced meat anything could have been said at the moment of death and if you don't believe in God, you cannot believe it will have an effect.