Animal charity raises concerns over 'frankenchickens'
Campaigners claim chickens are being grown so quickly on farms run by Tesco suppliers "they can barely stand up".
Open Cages said undercover filming showed fast-growing birds in "chronic pain" on farms in Gloucestershire and Herefordshire.
TV naturalist Chris Packham said it was "cruel beyond belief". He called for the use of slower-growing chickens.
Tesco said all its suppliers "adhere to some of the highest chicken welfare standards in the industry".
The animal welfare charity Open Cages said it carried out undercover investigations at two chicken farms during the summer.
The group's chief executive, Connor Jackson, said the footage showed "frankenchickens that were grown so fast they can barely even stand up".
"It's absolutely heartbreaking to see these animals unable to use their legs," he said.
"It defies belief that a British retailer like Tesco, is allowing such cruelty on their farms."
Chris Packham, along with 51 animal welfare experts, has signed an open letter to Tesco, urging the supermarket to sign the Better Chicken Commitment, which would mean only slower growing chickens are used.
"These poor chickens are living a nightmare," said Mr Packham.
"Being made to grow so fast that you can't even stand is cruel beyond belief, and it's a practice that has no place in British society."
Avara Foods, which owns the farm in Gloucestershire, said an internal investigation was carried out which "didn't highlight any welfare concerns".
A spokesperson said: "The undercover footage shows the overwhelming majority of birds are clean, in good health, moving freely and accessing food and water as they wish.
"The edited video, however, focuses on a handful of atypical birds that are either ill or have a natural deformity, neither of which are necessarily an indication of poor welfare standards."
Tesco said it had carried out its own independent audits at the farms and found that "all assurance schemes and legislative requirements were being met".
In a statement, the supermarket said: "We require all our suppliers to adhere to some of the highest chicken welfare standards in the industry… all our fresh chicken is British and meets or exceeds government-approved industry welfare standards, as well as Red Tractor."
It said it would "continue to monitor compliance against our own stringent welfare standards".