Should we buy organic or local food? Free-range or Fairtrade? Catherine Nixey weighs up the issues and takes her conscience shopping

Shopping conscientiously should be balm to the troubled capitalist soul; every right-thinking purchase leaving your heart a little lighter, your step a little springier in the knowledge that you are doing good with your wallet.

Shopping conscientiously should be balm to the troubled capitalist soul; every right-thinking purchase leaving your heart a little lighter, your step a little springier in the knowledge that you are doing good with your wallet.

But somehow it never works like that. Your intention is a simple utilitarian one: to do the greatest good to the greatest number - but the "goods" always seem to conflict. Do you go for seasonal, local mushrooms or organic Spanish ones? Organic coffee or Fairtrade? Do organic hens range more freely than free-range hens? Each purchase trails the sort of moral complexity that would have had that great philosopher Hume mopping his brow, and the well-intentioned shopper is left in a sort of purchasing paralysis.

So how can the harassed shopper assess which purchase is, morally speaking, the "best"? Simple, says Adrian Moore, professor of philosophy at Oxford: you can't. "Shopping by trying to calculate welfare and then make decisions that will maximise it is not, I think, a very easy thing to do," says Moore. "It leaves a lot of questions unanswered: what counts as welfare? Whose welfare are you talking about: the welfare of animals or of plants or the environment? Can you even measure welfare?"

So rather than trying to do an equation to balance the world's good and evil in your basket, Moore suggests a simpler approach. "Just ask yourself the question, 'Is this fair?'" he says. "So for example, if I buy cheaper bananas, then that might be benefiting me, but there are many people who suffer greatly because of it. So is that a fair arrangement?"

Which doesn't sounds too intellectual - or too much beyond the reach of the harassed shopper. However it's not entirely simplistic. According to Moore a little research is needed so that you can make an informed decision on which is fairest. What exactly are you buying? What do "organic", "Fairtrade", "local produce" and all the rest of them mean?

"'Organic' means that fruit and vegetables have been grown to a set of very strict standards," says Peter Melchett, Policy Director of the Soil Association, Britain's largest organic certifiers. No synthetic fertilisers or pesticides are allowed on organic fruit and veg, and only some naturally occurring pesticides may be used. As Melchett says, when you buy organic "you are very unlikely to be buying anything that has had any pesticides used on it at all". In the case of animal products "organic" means that the animals are reared to extremely high welfare standards. Firstly, unlike their non-organic counterparts, they are not routinely treated with antibiotics. They are also given more space. "Organic is the only way that you can really be sure that an animal, such as a chicken, is in a flock size small enough to allow it to get outside and move around," says Melchett. "That's not true of all free range chickens."

"All organic animals eat the sort of thing they eat in nature," says Melchett. "Which is why we didn't have mad cow disease: in organic farming you are not allowed to feed a cow's brain to a vegetarian ruminant."

Organic farming, because it doesn't use synthetic fertilisers and pesticides, also benefits the wild environment. Research has shown that there is more and more diverse wildlife on organic farms. Its practice also cuts pollution and fuel emissions: more than half of the total energy used on farms comes from the manufacture and transportation of these synthetic fertilisers and pesticides.

Organic food can help prevent pollution in a third way as well: food miles, the number of miles that food has travelled to get to you. For the conscientious shopper, the fewer, the better: it is wasteful to buy potatoes from Norway if you can buy them from Norfolk. Organic food scores well here; partly because it is often bought via farm shops or home-delivered boxes, so it tends to travel less far and partly because the Soil Association (successfully) lobbies the supermarkets to encourage them to source organic products from the UK where possible.

So if organic means you can put your conscience at rest with regard to things that are farmed, what about the people who farm them? How can you be sure that they are getting a fair deal? Appositely enough, through "Fairtrade".

"The Fairtrade mark guarantees that producers in developing countries have received a fair price," says Harriet Lamb, executive director of the Fairtrade Foundation. "Fair" here means a price which not only covers the cost of production, but which also leaves the producer with some left over to invest in their future. It also means the farmers are taking control of their own farms and their own future and that they are not under the influence of anyone.

"Fairtrade is about cutting out the middlemen; and bringing farmers in the developing world together into democratically organised groups," says Lamb.

While organic and Fairtrade marks are often seen together on products, Lamb is determined that they should never become integrated. "We are two very different schemes," she says. "We would never want there to be any confusion in the public's mind. The aim of organic is very different from the aim of Fairtrade. There are many disadvantaged producers in the world who, through no fault of their own, would never be able to go organic. We wouldn't like those farmers to be excluded from Fairtrade."

The fact remains that for products from developing countries you sometimes have to choose between whether to help people or whether to help the environment. There is still a little conscience-wrestling left to do in that instance. However, there is an increasing range of products that are both organic and Fairtrade. In the UK, the Soil Association has brought out a new "Ethical Trade" mark that not only means the product is organic, it also guarantees a fair deal to everyone - farmer, farm worker, supplier - in the food chain.

"The issues that confront agriculture in the developing world often confront agriculture here," says Michael Marriage, himself an organic farmer whose farm, Doves Farm, went fully organic in 1978. "Fair trade isn't about stopping people starving, it's about ensuring that farmers are not subject to the vagaries of the world market."

And this can, of course, affect a British pig farmer as much as a Costa Rican coffee producer. "The price of beef and cereals here is less in real terms than it was 20 years ago," says Marriage. "Ethical trading will ensure that the farmer gets a fair price. It is simply putting another constraint on rampant capitalism."

So buy an ethical trade product and you can be sure that the moral sifting has gone on on all fronts already, so you don't have to trouble your mind with it on your already fraught supermarket trips.

But, as Lamb says, shoppers shouldn't get so worked up anyway. "It worries me that people get so worried about it!" she says. "These labels make your shopping easier, not harder. All you have to do to buy conscientiously is to look for the mark. It is a shortcut to having the peace of mind that you want."

So there you have it: local is better than foreign; organic is better than non; fair trade is better than rampant capitalism, and organic hens do range freer than free range ones. And utilitarianism can be left on the shelf.