It is just a matter of time before a major animal welfare scandal hits organic food, according to a leading figure in the sector.

Soil Association director Patrick Holden told The Grocer that many shoppers would be disappointed if they knew how organic poultry and milk was produced on some farms. Production was often "semi-industrial", he said, and animals' treatment fell below consumers' expectations. It was in the sector's interest to expose those who let all producers down.

"The system is vulnerable to whistle-blowers because it's a very successful market," said Holden "It's going to happen and I welcome it." The statement followed last week's comments by Defra secretary David Miliband who dismissed organic as a lifestyle choice, claiming there was no proof it was healthier than conventional produce.

Holden said showing people how organic farming systems worked would encourage producers to reach the highest standards, rather than the EU minimum, on which some of the Soil Association's rivals' certification schemes were based. That was why he was helping Channel 4 to film a documentary examining the less palatable sides of organic production. "We have to open our doors," he said. On some organic poultry farms, birds were kept in colonies of up to 9,000 and many never got outside to roam, he said. Those that did were often faced with a stretch of barren ground that didn't allow hens to grub about for food. "There's a major gap between principle and practice in the poultry sector. Birds lay too many eggs, grow too fast and are disinclined to roam."

Organic producers used the same breeds of hen as intensive laying and broiler flocks, which could be inconsistent with the welfare element of organic principles, Holden said. The same was true on organic dairy farms, where soaring demand for milk was pushing farmers towards high yielding systems.