Organic ISN'T better than factory farmed: Why caged chickens have 'less stressed' lives than free-range Study found enclosed hens less likely to suffer from pecking or fractures High profile campaigns have pushed up free range egg sales dramatically But expert claims they could also have poor standards of living For consumers with a conscience, they are top of the shopping list. But it seems free-range eggs may not be all they are cracked up to be. According to researchers, hens kept indoors in cages lead happier lives. A study found birds raised in "enriched cages" enjoyed lower levels of stress and mortality, and were less likely to suffer from bone fractures or pecking than free-range chickens. Demand for free-range eggs, which cost almost double the caged equivalent, has risen steeply as a result of high- profile campaigns. 'Enriched': Researchers found hens in cages are more comfortable than we think with more protections Soaring sales: Sales in free-range egg have rocketed following numerous high-profile animal safety campaigns But Professor Christine Nicol, who led the research at the University of Bristol, said although free-range farms had the potential to offer birds a better quality of life than their caged counterparts, many had poor welfare standards. As a result, shoppers concerned about the well-being of birds should opt for eggs from caged hens, or those from free-range flocks that are part of a farm assurance scheme. Pugh's stressed egg "Caged hens are more comfortable than people think and have higher welfare as standard than free-range hens," she said. It would be nice to think the current free-range system gave the birds the best welfare, but the problem is that the management of free-range systems in the UK is so variable. Although you get some brilliant farms, you get some that are really not good. Prof Nicol added: "The challenge for the industry is realising the potential of the free-range system... so that they actually do what consumers think they do, which is provide all hens with good welfare." Battery farming of chickens, which involved five or six birds living in cramped conditions in a small cage, was outlawed in 2012. It was replaced by "enriched cages" - flocks of 70 or 80 birds living in stacked enclosures with access to food, water perches and scratching posts. Half of all eggs produced in Britain come from caged hens. But the majority of eggs sold in British supermarkets are free range. A carton of 15 cage eggs from Tesco costs £1.75, or less than 12p an egg. For a dozen medium free-range eggs, the price is £2.50, or 21p each. A spokesman for Compassion in World Farming said consumers should still opt for free-range eggs. She added: "Only in free-range (or organic) farms can hens fully perform all their important natural behaviours, like stretching and flapping their wings, perching up high, foraging, scratching, dust-bathing and laying their eggs in a comfortable nest."