As I said earlier:
1June 2017" The RSPCA, British Veterinary Association, the Farm Animal Welfare Council and animal rights groups say slaughter without pre-stunning can cause unnecessary suffering." That is good enough for me. If the professional organisation for vets does not support slaughter without stunning then who has equivalent professional standing to argue to the contrary?

I think it is quite safe to assume the necessary studies have been carried out to support this position.