An investigation is under way into the practices at a Somerset abattoir, after animal rights activists released shocking hidden camera footage.

The video, which has been posted on the internet, shows a worker at the AC Hopkins slaughterhouse near Taunton stunning a ewe while it was suckling a lamb, failing to stun pigs, sheep and calves sufficiently and even standing on a semi-stunned pig to reach a hook.

The video has been labelled 'shocking and cruel' by the campaigners who obtained the footage.

It was enough to spark a major investigation of the abattoir at Creech St Michael.

The slaughterman concerned has already had his licence suspended by the authorities.

The Meat Hygiene Service, which is investigating the video, said there was evidence of 'serious breaches' of animal welfare legislation, and added that animal cruelty within a slaughterhouse 'would not be tolerated'.

A spokesman for the slaughterhouse admitted the conduct of the individual had not been 'up to standard', but said Animal Aid obtained 40 hours of footage of work in the abattoir and released little more than half an hour of film they deemed to be unacceptable.

In April this year, undercover investigators got into the slaughterhouse and fixed a hidden camera high above the stunning pen, where animals are taken in groups of up to a dozen. The footage shows the slaughterman stunning the animals one by one with long electric stunners. He then hooks up one of the back legs onto a moving hoist, which takes the animal away into the 'blood room'. As the animal leaves, the slaughterman appears to slit the animal's throat.

The footage released by Animal Aid shows the slaughterman struggling to properly stun animals, including a group of ewes and their lambs. On one occasion a ewe is stunned while its lamb is still suckling it, and a lamb is stunned while trying to hide underneath its mother.

Many times, the animals that have been hooked upside down are still showing signs of movement or appear to have already come around. Several pigs, for instance, come round and kick so much against the hooks, that they free themselves and fall to the floor of the blood room, lying on a floor that is inches deep in blood. On another occasion, a pig that has been insufficiently stunned falls from the hoist and the slaughterman stands on it to subdue it while reaching for the hoist.

In the light of the Hopkins footage, Animal Aid called for tighter regulations on slaughterhouses, including CCTV to be placed in all abattoirs in the UK. They want a change in the law to make ongoing training and assessment mandatory for all abattoir workers, the worker at Hopkins to have his licence revoked and to be prosecuted for animal cruelty, and an independent investigation into the practices at Hopkins.

"We believe that millions of animals across the country are suffering untold torment when they are stunned and killed," said Kate Fowler, from Animal Aid.

"In the stun rooms, we filmed terrified sheep and pigs running crazily in circles, looking for an exit. Many animals were partially stunned or left writhing or convulsing on the floor, while the stun operator ignored their plight. Animals were kicked, hit, goaded, sworn at and stood on. In our view, one worker in particular combined incompetence, stupidity and callousness. But even those workers who function as best they can, operate in a system that is pitiless."

Last night, it appeared some of Animal Aid's demands were already being met. The Meat Hygiene Service said an investigation was underway into AC Hopkins, and the worker concerned's licence had been revoked.

"Animal cruelty within a slaughterhouse will not be tolerated," an MHS spokeswoman said. "The MHS has reviewed the Animal Aid footage and there is evidence of serious breaches of animal welfare legislation in one out of the three slaughterhouses filmed. We have been in contact with the slaughterhouse concerned and one slaughterman has had his licence suspended.

"Official MHS vets work in every slaughterhouse across Britain and make regular unannounced checks to ensure that the slaughtering process is humane. However, we cannot inspect every animal and bird at the point of slaughter and full responsibility for animal welfare rests with the operators of slaughterhouses."

Stephen Lomax, a lawyer for the Association of Independent Meat Suppliers, spoke on behalf of AC Hopkins. He said Animal Aid had hidden cameras in three slaughterhouses – the other two were in Cornwall and Derbyshire, and had obtained 40 hours of footage, but released just half an hour at Hopkins'.

"That tells its own story," he said. "This is an isolated incident. The operator involved was not perfect. The livestock industry aims to achieve the very highest standards of animal welfare, not just compliance with legislation.

"Although they are not abdicating responsibility, AC Hopkins would have hoped that as there is an official vet on the premises at all times, if they have any problems with welfare, the vet would have drawn their attention to it. They are entitled to assume the vet would have spotted this," he said.

He added that the employee had only worked for the company for three months, having worked for years at another large abattoir which recently closed.

"He was employed as an experienced slaughterman. He is currently not working with live animals, and the matter will be investigated without prejudicing the result of that investigation," he said.

Last night the RSPCA said it was 'disappointed' that it had not been alerted by Animal Aid. A spokesman said: "The RSPCA is always disappointed when concerns about animal welfare are not reported to us directly and promptly, as without a formal complaint we are unable to act,"

"In this instance, we have only just been made aware of the situation by the Western Daily Press, and some of the footage is already more than six months old. We would urge anyone with animal welfare concerns to contact us or the relevant body straight away so we can investigate or alert the relevant authority.

"Having viewed the footage we do have major concerns about the unacceptable behaviour and treatment of the animals.

"The footage also appears to highlight design faults in the premises themselves and we would hope the MHS and Trading Standards would identify areas to improve within these systems to avoid these scenarios happening in the future," she added.