Sky News has uncovered shocking animal welfare conditions at a UK horse abattoir.
They include animals being beaten, neglected and illegal procedures in the process of slaughtering British horses destined for European food markets.
It comes amid public anger that some of our biggest supermarkets have been selling beef burgers and other products that contained horse meat .
Sky News visited the Red Lion Abattoir near Nantwich in Cheshire after concerns were raised by Animal Welfare Group Hillside Animal Sanctuary.
Investigators at Hillside fitted secret cameras which filmed horses being beaten with an iron rod to encourage them into the pens.
Some were then crammed into the slaughter pens in pairs and, on one occasion, a group of three, before being stunned together.
In harrowing images the horses fall on top of each other. Under The Welfare of Anim als Act 1995 , horses should not be slaughtered in sight of one another because of the distress it causes.
Furthermore, Sky News found that sick or injured horses were left untended overnight rather than put down immediately.
As a result of the investigation, two slaughter men have had their licences revoked.
Craig Kirby, head of approvals and veterinary advice at the Food Standards Agency (FSA) told Sky News: "As soon as we got the footage and reviewed it we took immediate action to revoke the slaughter men's licences.
"That means they cannot work to slaughter animals again. We will also look to gather further evidence to see if we can prosecute."
Former government chief veterinary officer Keith Meldrum, who viewed the footage, said he was shocked by what he described as "appalling" welfare breaches.
"We see three animals stunned at the same time and it is totally illegal and contrary to welfare slaughter regulations," he said.
"It's a significant welfare problem for a number of reasons. It's harder to render them unconscious in a group and they have a higher chance of regaining consciousness before you've completed the procedure."
Another incident filmed included a horse that appeared to come round from the stun while being hung upside down before being bled. Mr Meldrum described it as "totally and completely unacceptable".
FSA statistics released to Sky News show a dramatic increase in the number of UK horses slaughtered every year, from 3,859 in 2007 to 8,426 in 2012.
Depending on the size and breed they are bought for anything between £100 to £300 and can fetch around 700 euro on the European meat markets.
The animals come from a variety of backgrounds. Some are former pets, others come from show jumping or the race track.
A report last year from the British Horseracing Authority (BHA) found: "The number of thoroughbreds reported dead to the Horse Passport Issuing Authority rose by 580 - an increase of 29% - from 1994 to 2574 horses.
"Of these, 1127 horses either in training, breeding or out of training were reported as killed in abattoirs - and reported to the Government Meat Hygiene Service - from 499 horses in 2010, an increase of 126%."
However, in a statement to Sky News, the BHA added: "This is a wider equine issue and not an issue for the British racing industry, which is one of the country's most highly regulated equine pursuits.
"However, if there are allegations that any horse, whether thoroughbred or not, is being inhumanely treated in an abattoir we would fully support any investigation and subsequent action, if appropriate."
During the investigation, Hillside Animal Sanctuary rescued one racehorse called Underwriter by bidding against the abattoir at auction. They discovered it had a distinguished career.
John Watson, from Hillside, said: "It's not just ill and old horses being killed. There are very many fit and healthy horses, horses with foals, pregnant mares, and thoroughbreds that are being treated badly.
"It blows away the myth of humane slaughter, and there is a misery in that place that is palpable."
Hillside's lead investigator, who did not want to be identified, added: "What we've found has shocked us deeply; animals left with horrendous injuries and horses shot on top of each other.
"In all the years I've been doing this work, without doubt it's the most harrowing experience I've come across. All the horses in there had their heads hung down."
The Red Lion Abattoir told us it views animal welfare and public health with paramount importance.
In a statement it said: "In attendance at the The Red Lion Abattoir are three full time Food Standards Officers comprising of an official veterinarian and full-time meat hygiene inspectors throughout production."
It said the incidents were "not the norm, but of an isolated nature" and they have taken disciplinary action against the individual featured.
The statement continued: "I agree horses should individually enter the stunning area and most certainly not three at a time.
"However, small horses and ponies having spent years together as companions are difficult to separate. Horse lovers would understand that.
"My opinion and that of other veterinarians is it is better to keep those types together to reduce the stress, providing swift dispatch is achieved."
The Red Lion Abattoir also insisted it meat was not part of the recent supermarket burger scandal.
The horses there are destined to be served in European food markets. The scandal this time is the way they are treated, in the last moments of their lives, in a licensed British abattoir.
Roly Owers, chief executive of World Horse Welfare , viewed the footage and said: "The breaches, from what we've seen, are throughout; from the care of the animals to the slaughter process.
"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. There are, without doubt, welfare issues here and it is plain illegal."
The RSPCA said "The footage is shocking and upsetting to watch." They have requested a full copy of the film with a view to investigating.