Shocking images that are claimed to show a sow being eaten alive by other pigs on a British farm were released by animal welfare activists yesterday.

An undercover investigator from the campaign group Viva! says some pigs at the farm – which supplies pork to Tesco – were suffering from 'extreme distress'.

The group first highlighted conditions at Hogwood pig farm in Oxhill, Warwickshire, last year. However, officials who investigated found no breaches of animal welfare standards and Tesco continued using it as a supplier.

An undercover investigator from the campaign group Viva! says some pigs at the farm were suffering from 'extreme distress'

Viva! revisited the farm this month. They released footage including images that the Mail has decided are too distressing to publish. One scene shows a sow slumped forlornly in a narrow passage as three pigs, their snouts smeared with blood, take turns to gnaw at her hind legs. The investigator said: 'My stomach began to churn as I watched … her flesh bitten from the bone. I was mortified.'

Viva!, which campaigns for veganism – a diet free from meat, poultry, fish, eggs and dairy produce – has reported its findings to the RSPCA but claims animal suffering on farms is widespread.

Founder and director Juliet Gellatley said: 'Cannibalism is not natural behaviour for pigs and is caused by this bleak environment. I believe anyone with a heart seeing the state of the animals in today's modern farms would want factory farming to end.

One scene shows a sow slumped forlornly in a narrow passage as three pigs, their snouts smeared with blood, take turns to gnaw at her hind legs

'Hogwood Farm is not some aberrant little farm, it is large scale with about 16,000 pigs and typifies large scale institutionalised cruelty, and it must end.'

Hogwood Farm's owner, Brian Hobill, was unavailable for comment yesterday. But following allegations made by Viva last year, he said pictures taken by an 'extremist vegan group' did not represent the general health of his animals.

Red Tractor said: 'No major alarms have been raised by our independent inspectors'

However, he admitted: 'There do appear to be shortcomings on dead stock removal. We will review our policies and ensure these are followed. The care of our animals is our top priority.'

Guidelines from Government food department Defra and the Farm Animal Welfare Council say dead animals should be removed swiftly. A Tesco spokesperson said: ‘We take all concerns extremely seriously and therefore have immediately launched a full and thorough investigation following this video footage.

Animal welfare is a priority to us, and with the RSPCA, government approved vets and Red Tractor we regularly inspect all the farms used by our suppliers to ensure they meet the highest standards.’

Red Tractor, formed in 2000 and now the UK's biggest assured food standards scheme, said: 'No major alarms have been raised by our independent inspectors, the specialist pig vets, the Animal and Plant Health Agency or Trading Standards, who have all inspected the farm in recent months.

'The last inspection on July 6 did raise an incidence of low-level tail-biting – a behaviour that pigs may display in both indoor and outdoor settings.

Hogwood Farm's owner, Brian Hobill, was unavailable for comment yesterday

'The farmer has been implementing management of this under the supervision of the vet. Independent inspectors are happy that this is being well managed.

'The unannounced inspection on July 6 did not find evidence of the most distressing images alleged in the Viva! film. We continue to watch Hogwood Farm with vigilance.'

The RSPCA said: 'We were concerned to hear reports from Viva! and arranged for a vet to attend the farm the same day. The vet, accompanied by the police, found no injured pigs.'