http://www.youtube.com/watch?v=I41IYWb_Mus
I remember watching this documentary on the BBC when originally produced. Not only does it show the slaughtering process of animals but goes deep into the social /political hierarchy and ethnic backgrounds of the workers. Some characters involved !
Also covers Kosher and Halal slaughter.
I hope you don't find their Northern accents too 'broad' to understand.
Contains 'strong' language and political views...., but overall, it's a decent documentary on how the employees ended up working at a slaughterhouse.