Animal welfare in slaughterhouses is one of the few areas that the supermarkets can be seen as the guys in the white hats. Their guidelines and conditions for using a slaughterhouse as a supplier exceed the conditions in government legislation. This is of course customer led, the public want (as far as possible) humanely slaughtered meat and pressurizes the supermarkets to supply it. I realise how relative this concept is. Hopefully this trend will not reverse thanks to this short sighted government u turn. Customer pressure may limit the impact.
I work as a Killer at a slaughterhouse and have seen the condition and treatment of animals improve dramatically in the last 3 years. There has been no new major legislation in that time. What change there has been has been on the insistence of the supermarkets who have the money for the regular audits required to ensure compliance. The Food Standards Agency does insist on independent vets (through an agency called the MHS) being present on sight throughout killing to guard against both cruelty by sadistic employees and (the more common) cruelty through a poor killing process, but the extra customer pressure has had more effect. The sad fact is that even the crumb of humanity we can offer to an animal going through a horrific process comes with a price tag.
The words I use such as "process" and "procedure" are not used lightly. A modern poultry slaughterhouse will kill 350,000 chickens a day. To suggest that such numbers are possible with all but the most cursory regard for animal welfare is laughable.