By Simon Cox
Presenter, The Investigation
Borough Market in South London is the granddaddy of farmers markets. On a Wednesday lunchtime there is a big queue at the organic salad bar. Next door there's a steady stream of customers at Betty's organic stall stocking up on organic herbs and spices.
For many consumers, there's a belief that eating organic will improve their health. It's one Betty supports.
"Given a choice would you eat something that is covered in artificial chemicals to something that is natural and clean?"
Can we prove that organic is better for our health?
The Soil Association, Britain's largest certifying body for organic produce, claims there "is a growing body of research that shows organic food can be more nutritious for you". And there have been some recent studies to back this up, showing higher levels of vitamins in organic kiwi fruits and tomatoes.
The organic lobby's claims failed to convince her. The BNF "feel it would be irresponsible to promote organic food over non organic food as being better for you as there is not enough strong evidence," Ms Williamson says of her findings.
The government and its independent watchdog, the Food Standards Agency are equally adamant there is no proof organic food is better for our health. But science alone cannot prove the point, says Lord Peter Melchett, a director of the Soil Association, who believes consumers must trust their instincts.
"Science doesn't tell us the answers so some of it we have to go on feelings," he says.
One fact that can't be disputed is that organic farming uses far fewer pesticides than conventional agriculture. The Soil Association's booklet Organic Food and Farming: Myth and Reality, is clear what this means: "pesticides have a harmful impact on human health".
So organic must be better for your health as it rarely uses pesticides... Currently the amount of pesticide residues on fruit and vegetables isn't high enough to harm us, says the Food Standards Agency.
"All of us on average consume several thousand a day," says to Professor Trewevas, who estimates this amounts to a quarter of a teaspoon a day. These natural pesticides don't adversely affect us, he says.
"You do not come out in tumours; you do not become sick from nerve toxins."
But buying organic isn't just about health, for many people it's about helping to save the planet. Sheepdrove farm in Berkshire is an idyllic picture of rural life. Sheep and cattle graze on some of the 2,000 acres of rolling hills, while below them chickens roam freely.
Laurence Woodward, director of the nearby Elm Farm Organic Research centre, believes Sheepdrove is a perfect advert for the environmental benefits of organic farming.
"There is no question that organic farming is better for the environment than conventional farming, there is mounting evidence from government studies," he says.
But, as with the health claims, can we prove organic really is better for the planet?
His findings weren't good news for the organic industry. "The studies that exist show there is not a clear cut thing that says let's go organic and that will have a big environmental impact compared to traditional methods of farming," says Mr Green, summarising his findings.
The organic lobby rounded on the study accusing it of bad science because it was only a "literature review" rather one based on original research. But Lord Melchett, readily concedes there are "still some big gaps in our knowledge about this". He is confident future research will prove organic is better for the environment.
But few studies have actually tried to analyse the environmental benefits of organic farming. Mr Woodward believes there's a good reason for this: "It's almost impossible to do a sensible comparison of organic and conventional farming systems. The systems are so different".
Yet this hasn't stopped bodies like the Soil Association from claiming that "Organic farming is friendlier to the environment".
But challenged on this, the Department for Environment, Food and Rural Affairs, not surprisingly, says it doesn't favour one form of farming over another.
Not all organic consumption is about saving the earth. It is about rearing and caring for livestock more humanely. We have uncovered evidence of serious concerns from insiders about the way some organic meat is produced.
Laurence Woodward, who led a study to be published later this year, says conditions at some pig farms in Holland were not "organic" since "they are kept indoors, in cramped conditions.
"It's very much conventional, very intensive," he says.
What of the consumers who buy this meat? "There is no other way of saying it - they being conned," says Mr Woodward. The research didn't identify which of the UK's certifying bodies was approving these overseas products.
But when it comes to endorsing organic produce from overseas, the Soil Association, for one, doesn't send its inspectors directly. Rather "what we do is inspect the inspectors and make sure they are going to inspect to our standards," says Lord Melchett.
Being an ethical consumer was never going to be easy. The politics of produce is confusing and getting more complicated each day. The best advice, don't believe simple labels that promise the earth but without the science to back it up.
The Investigation is broadcast on BBC Radio 4 on Thursday 26 April at 2000 BST.