Pigs lie in cramped squalor and are left for hours to die in footage revealing the “grim reality” of farming.
Animal welfare campaigners say the scenes caught by a hidden camera at a Red Tractor-assured farm are some of the worst they have seen.
Animal Justice Project filmed for three months at Bickmarsh Hall mega-farm in Warwickshire, where 8,000 pigs are housed in 46 sheds.
The site rears them for pork producer Cranswick Country Foods, which supplies Asda and Tesco.
Footage shows one pig being cannibalised, while a shivering and groaning piglet is trampled on and bitten by others. Staff took up to 13 hours to remove them, Animal Justice Project said. Farrowing crates, which are legal and confine pregnant and nursing sows, were also in use and bins were piled high with corpses.
Pigs were kept in pens with no bedding, just hard slats, and investigators said many were covered in excrement. They were also documented biting and fighting, with only five feed troughs for more than 25 animals.
And cameras captured some staff kicking and slapping pigs when moving them around.
Red Tractor, which says its logos on supermarket food “underpin high standards of British food and drink”, said its investigation found the farm was in compliance with its animal welfare standards.
It added: “Protecting health and welfare is a top priority.”
But Animal Justice Project said some of the scenes it filmed, such as pigs unable to bear weight on all four legs, potentially break welfare regulations and industry guidelines.
Founder Claire Palmer added: “Our footage captures the grim reality for pigs on farms in Britain.
“Consumers must be asking themselves, is a bacon sandwich or pork pie worth that?
“Red Tractor’s claim that our footage shows a farm compliant with its welfare standards makes it clear this scheme is not fit for purpose. It exists to protect profit and act as a mouthpiece.”
Former pig industry vet Dr Alice Brough said the footage shows “the epitome of squalor and unfortunately represents the norm for a large proportion of Britain’s pig farms”.
Cranswick said it takes animal welfare seriously and made an unannounced audit of Bickmarsh Hall after seeing the footage.
It added: “The unit was found to be operating to the required standard.”
Tesco and Asda said they took the allegations seriously and were investigating.
Tesco added: “All of our pigs are reared to recognised farm assurance standards such as Red Tractor, RSPCA Assured, as well as our own.”