The RSPCA said that the new rules could also be beneficial to consumers, after a study by the European Food Safety Authority reported that thinning is linked to increased rates of campylobacter in chickens.

Dr Marc Cooper, chicken welfare specialist at the RSPCA, said: “Our ban on thinning will be a major step forward for the welfare of chickens.

“Once again the RSPCA is leading the way on farm animal welfare by setting these pioneering standards for indoor reared chickens and we hope other farm assurance schemes will follow suit.”

The thinning process involves rearing the birds to the maximum stocking density permitted and then removing a proportion of them to lower the density. This can take place several times before all the birds are finally removed from the shed.

The animal welfare organisation said that thinning can be a stressful experience for the birds as their feed is removed to allow catching teams to round-up the birds more easily. The RSPCA added that the temperature inside the shed can also drop, particularly during the winter, as teams of catchers enter.

Dr Cooper added: “I hope that producers who are not currently rearing to RSPCA welfare standards will follow suit and ban thinning but without implementing other compensatory management practices, such as increasing stocking densities, that could have a negative impact on welfare.”

From January 1 2016 farmers rearing to RSPCA welfare standards under the RSPCA Assured label will not be permitted to thin their flocks.