Footage secretly filmed by Animal Aid appeared to show abattoir workers hacking at sheep’s throats while they were still alive and punching and kicking the animals.
Farmers whose lambs are processed by the abattoir have called Farmers Guardian to express their distress and concern at the allegations.
Islamic practice requires animals to be killed with one clean sweep of a knife to prevent suffering.
The charity said the footage from Bowood Lamb abattoir, Thirsk, showed the animals being treated with ‘gratuitous violence and contempt’.
It has intensified demands for a complete ban on the religious slaughter of animals without prior stunning.
Four slaughtermen have had their operating licences suspended by the Food Standards Agency (FSA).
A spokesman for the FSA said: “The FSA takes animal welfare at abattoirs very seriously, which is why we immediately suspended the licences of the slaughtermen involved.
“There is no excuse for treating animals in the way shown on the video and we are therefore investigating the footage with a view to prosecution. We are also continuing to investigate all the circumstances around the incident to ensure proper safeguards are introduced to stop this happening in the future.”
It comes after an FSA survey of slaughterhouses in Britain showed an ‘improved picture’ regarding compliance, compared to the 2011 survey.
The agency said CCTV uptake for animal welfare monitoring had increased, however it said there were still areas where improvements were required.
Back in 2012, Animal Aid exposed alleged cruel treatment of pigs at Cheale Meats, Essex, where it was claimed workers were stubbing out cigarettes on the animals.