Peter Barton is as uneasy as the rest of them. The organic poultry farmer has 50,000 hens scuttling around his fields in East Sussex. He, like many farmers, thought if anyone was going to be hit by bird flu, it would be someone like him. "We are obviously very concerned about what has happened, but it's not a total surprise," he says. "We've been expecting this for the last two or three years. However, I am very surprised how it turned up on an intensive farm rather than on one of ours. They are able to have much higher biosecurity. Our birds just run around and come into close contact with all things wild and natural. It flies in the face of logic. Something has gone wrong somewhere."

Thankfully Grassington Farm near Lewes, which produces organic chicken eggs and pullets, is a long way from the turkey farm in Holton, Suffolk, where Britain's first case of the H5N1 strain of bird flu broke out last week, killing 2,600 turkeys and leading to the slaughter of 159,000 more. But there are about 62 free-range or organic farms in the controlled zone around Holton. Defra requires farmers to house their poultry or isolate them from wild birds, by, for example, netting them, and feeding them and watering them indoors where possible. Organic and free-range farmers throughout the country are being urged to maintain high levels of biosecurity and develop plans to enable them to bring their birds inside if required.

"A high standard of biosecurity, separation of poultry from wild birds and careful surveillance for signs of disease remain the most effective means of protection," says a Defra spokesman. "We do not intend to permit the vaccination of birds as an immediate disease control response."

Peter Barton has the facilities to keep his birds inside, not that he wants to. "To protect them we would have to [bring them inside] if Defra advised us to," he says. "At the moment they haven't, but that could change soon. We have to protect the welfare of the birds, and our staff. We all live and work on the farm, so we live cheek-by-jowl with our birds."

The Food Standards Agency has already received calls from worried members of the public concerned about the safety of eating poultry. Barton believes that the current scare might work in the favour of organic farmers. "If anything, in situations like this the consumer tends to move towards extensive systems rather than intensive systems. [Scares] can be a bit of good news for the smaller farmer."

Robin Maynard, campaigns director for the Soil Association, is relieved that the outbreak wasn't at an organic or free-range farm. He claims that some in the intensive poultry industry had predicted that such farmers would be responsible for bringing bird flu into Britain.

"We are very keen that the public still supports organic and free-range. It's one of the success stories in farming," he says. "People are surprised to learn that 8,000 turkeys were kept in one shed and they've had to slaughter 160,000 overnight. That is why turkey is so cheap. But the turkeys live much shorter lives, they don't get fed the type of food that organic and free-range birds get and they are kept in pretty inhumane conditions. That's why organic and free-range turkey costs more, tastes a lot better and you can eat it with a clear conscience. What we don't want to see is the industry wiped out by unfortunate incidents such as this."

He claims there is "interesting evidence" to suggest that organic and free-range poultry may have naturally stronger immune systems than those reared intensively. "The whole principal of organic farming is built on positive health and naturally immune livestock poultry. One of the examples that supports this is the fact that there was an outbreak of a different strain of bird flu, H7, in Norfolk last year. It was identified in an intensive indoor broiler flock and there was a high mortality rate. About 15 days later a vet from a nearby free-range unit rang up and said he thought they may have had it first. There had been a much lower mortality rate. Defra vets confirmed it was H7 and that it had broken out there first. But because the birds weren't packed so closely together and were going outdoors they hadn't died off so much or spread the disease so quickly."

The farm animal welfare organisation Compassion In World Farming (CIWF) has no qualms in blaming factory farming for what it calls "the myth" that wild birds have caused the current bird-flu crisis. "Factory farming was always bound to cause a disease backlash by pushing nature way beyond its limits," says CIWF's chief executive, Philip Lymbery. "Keeping massive numbers of poultry on intensive farms worldwide is now coming back to bite us in the form of avian influenza."

Intensively farmed poultry is often kept in overcrowded conditions that provide an ideal breeding ground for disease, the charity claims. The chronic stress to which the birds are subjected could also weaken their immune systems.

However, the British Poultry Council denies that factory farming is to blame. "I think that would be pure speculation," says a spokesman. "The most predictable way of avian influenza spreading remains via wild birds, and I don't think the question of intensive farming is something that should be considered in the spread of bird flu."

Neither does the NFU agree with Philip Lymbery. Maria Ball, the union's chief poultry adviser, says: "I don't know where the science is in his statement and I would not support that view at all." Blaming one part of the industry is "irresponsible", she adds. "Avian influenza is a disease that affects all poultry. It doesn't recognise any differences between free-range, organic or conventional types of production. The virus will freely attack any sort of poultry, however it is kept. When we had low-pathogenic avian influenza back in the spring that occurred on two free-range farms and then went into a broiler breeder unit and we understood it was by fox carriage."

Peter Barton, meanwhile, refuses to worry about the future. "Our birds are pretty robust," he says. "That doesn't mean that they won't get the disease if it becomes endemic. At the moment it just seems to be a breakdown somewhere along the line. What we would be concerned about is if large numbers of wild birds were found to be dead or dying, which would indicate that the disease has spread into the country. There is no evidence of that at the moment, thank goodness."

What is free-range?

* To qualify as free-range, the birds must have access to at least an acre of land for every 400 birds.

* To be certified organic, the birds must be free-range and fed on a diet produced without artificial fertilisers and pesticides. The use of medicines is restricted and flock sizes are smaller.

* In factory farms, birds are fed antibiotics to help prevent disease spreading.

* Free-range flocks are more vulnerable to exposure to avian flu through contact with wild birds. But free-range farmers argue that intensive farming helps to spread disease and that their birds have a stronger immune system and more resistance to infection.