Horrific images show distressed horses come round from being stunned only to find themselves hanged upside down ready to be bled.
The video was filmed by hidden cameras, at Red Lion Abattoir, near Nantwich, Cheshire, during a Hillside Sanctuary investigation.
The animals were being beaten with a metal rod and crammed into pens together before being slaughtered. Separately, some injured or sick horses appeared to be left by staff to suffer overnight.
Last night the Food Standards Agency said it revoked the licences of two slaughtermen after a probe into the video, meaning they cannot work to slaughter animals again.
The number of horses being slaughtered in the UK has more than doubled in the past five years.
FSA figures show 8,426 were put down in 2012, compared to 3,859 in 2007.
Horses are sent to the abattoir when they are old, sick, injured or retired.
The shocking footage, which was shown on Sky News yesterday, comes just days after it emerged that horse meat had been found in beef burgers and was being sold by leading supermarkets across the UK.
John Watson, from Hillside, said: “It blows away the myth of humane slaughter. There is a misery in that place that is palpable.”
Horses are intelligent animals. When they see an animal stunned in front of them, you can only imagine the distress that animal is going through.
In response, a Red Lion spokesman said: “The incidents, whilst captured on limited filming are not the norm but that of an isolated nature…"
GRAPHIC FOOTAGE: VIEWER DISCRETION IS ADVISED
Once again, an animal rights campaign group shows more evidence of cruelty and lawbreaking in slaughterhouses. The problems are serious and widespread. Other investigations into abattoirs have revealed animals being kicked, slapped, stamped on, and picked up by fleeces and ears and thrown into stunning pens. Animals being improperly stunned and going to the knife while still conscious, is the norm in mainly all slaughterhouses.
Each year in the UK alone, approximately 1,000 million animals are farmed and killed for food.
All animals, whether they are horses, cows, chickens, pigs or fish can feel pain and suffer. If you care about those horses who were killed for their meat, and believe that animals should not be harmed unnecessarily, then please spare a thought for all those other animals, and make the compassionate decision, by adopting a diet free from animal products.
Learn more: changeinyourhands.org