An ex-Morrisons employee has said the supermarket sold genetically-modified “FrankenChickens” as “high-welfare” and “cruelty-free” poultry.
Doug Maw, who was sacked from the Bognor Regis branch last month, was “shocked” by the retailer’s claims.
However, Morrisons said it acts “swiftly and decisively” against any “malpractice” in its supply chain.
An Open Cages investigation found this year that Cranswick, a meat processor, was supplying the rapidly-growing chickens to Morrisons.
The birds can reportedly go from 40 grams at birth to four kilograms within eight weeks.
Speaking to BBC Radio Sussex, Maw said they developed so quickly that they had “broken limbs” and, in their cramped conditions, would eat each other.
“It’s just horrific,” he said.
Maw came across the investigation online and shared a petition on banning “FrankenChickens” through a Morrisons Facebook group.
“As I was working at Morrisons I thought that might give me some chance to speak up from inside,” he said.
Maw, who organised a protest against the grocer in August, was sacked on October 22 after more than five hours of disciplinary hearings.
Morrisons said he was dismissed over “other disciplinary matters”.
“In fact, Doug was both offered a meeting to discuss his points with our head of agriculture and an opportunity to present his views to our chief executive,” a spokesperson said.
According to Maw, Open Cages has written to “literally every chicken-supplying store and company in the UK” about improving poultry conditions.
Morrisons was apparently the only business that did not respond.
Other retailers have “talked about how they might change over time to eliminate this kind of fast-growth ‘FrankenChicken”, he claimed.
In response, a Morrisons spokesperson said: “All our regular chicken is raised to above Red Tractor standards.
“We are also the only retailer in Europe to ask our fresh chicken suppliers to require chicken to be born into the barn in which it will be raised by 2025.”
Around 80 per cent of its fresh chicken – no mention was made of frozen or processed – is said to meet this standard already.
The spokesperson continued: “In February we said that we would be producing a range that adheres to all nine of the BCC [Better Chicken Commitment] standards which will be in store in early 2022.
“All our chicken already adheres to seven of the nine standards.”
The BBC commitments include banning cages, providing a proper level of light and ensuring that chickens are not housed in cramped conditions.