How could such a system - apparently eschewing all the innovations that produced a new era of cheap food and made British farming the most efficient in Europe - ever hope to feed the world?
With farmers falling over themselves to convert to organic and some experts predicting that up to 30 per cent of Britain's agricultural land could be farmed organically in a decade from now - the current proportion is about 1.5 per cent - such strictures are beginning to look a little hollow. We're also far more aware of the true costs of our "efficient" agriculture: not least a devastated countryside. Take that symbol of the small-scale British rural landscape, the hedgerow.
Forty per cent of our hedgerows have vanished in the past half-century, enough, it has been calculated, to stretch four times round the world. They are still disappearing at the rate of 10,000 miles a year, and with them birds and insects that were characteristic of traditional farmland - the corncrake, for example - have dwindled near, and sometimes beyond, the point of extinction.
You can't, of course, put a value on the corncrake, or on the (now extinct) short-haired bumble bee. But there are other back-of-envelope calculations that you can make. Over the past 10 years, for example, the water industry has invested an extra pounds 31bn on cleaning our water supplies. It is a cost which customers have paid through increased bills but for which conventional farming, as one of the main sources of water pollution, particularly pesticides, is partly responsible.
There's also the steady rise in food poisoning, blamed by many on intensive food production and thought to cost between pounds 1bn and pounds 3bn each year. There's the pounds 4bn bill for the BSE crisis, picked up directly by the taxpayer. According to Dr Carlo Leifert, of Aberdeen University's Centre for Organic Research, if that pounds 4bn had been spent subsidising organic meat sales over the past decade, it would have been cheaper than factory-farmed meat.
There's no doubt that conventional farming carries an often invisible price tag and that organic farming is far kinder to the environment. But will it be able to cope with supplying much more - possibly most - of our food without a lasting increase in prices?
The best answer is that we don't know yet. In fact, we can't know, because there has never been a fair comparison between the two types of farming - but there seems no overwhelming reason why it should not.
The equations are complex, however. Most studies which have tried to compare the two systems as they operate in Western Europe suggest that crop yields are between 20 and 40 per cent less in organic farming; equally many of the overheads - notably chemicals and fertilisers - are lower. Labour costs are higher - up to 30 per cent more people are needed to work organic farms - but this may count as a social benefit: one could equally say that organic farming creates jobs.
A recent 10-year study in the US showed only one per cent difference in maize yields between organic and conventional farming, although there were major differences in environmental impact. Soil fertility increased dramatically under organic management but declined in the industrial trial.
According to a recent study by Greenpeace and the Soil Association, comparisons are impossible because of the small sums spent on organic research. Even now, despite the organic renaissance, the Ministry of Agriculture, Fisheries and Food (MAFF) still spends 60 times more on research into conventional farming. The potential of modern organic farming is thus "largely unrealised", the study argues.
Dr Nic Lampkin, an organic agriculture specialist at the Welsh Institute of Rural Studies, also points out that Western European comparisons may not apply elsewhere. In other parts of the world organic yields are as high or higher than conventional systems. Dr Lampkin argues that poor farmers in developing countries cannot afford expensive feedstocks and chemicals, and that the damage caused by industrial farming means that simply transferring it from the developed to the developing world - what one authority has called "saving the planet with pesticides and plastic" - is "not a sustainable option".
The effect on prices and food security are difficult to assess, however. The world, overall, isn't short of food - malnutrition in developing countries is the result of a complex mix of economic and social factors. In Europe, indeed, we are over-producing: governments are trying to get 10 per cent of arable land taken out of production.
Last year pounds 76m was paid to farmers in England and Wales to "set aside" their land - a form of indirect subsidy to environmental protection which many argue would be better spent on support for organic farming. Some experts also believe that widespread adoption of organic farming might generate more home-grown food in Europe. Land in developing countries now used to grow cash crops for export to the West would then be freed for production for local people.
Given the premium prices now being paid for organic produce, according to MAFF, most types of farm would benefit if they switch from conventional to organic. As organic production expands, this premium may disappear - and prices should fall. But if they don't, and the era of cheap food recedes into the past, is this necessarily a bad thing? We may end up paying more for our food, but less to repair the damage to our health and environment.
Dr Lampkin believes that a large-scale switch to organic could produce better incomes for all farmers and that this can be achieved without compromising international food security. Conventional producers, "far from being threatened by organic farming, should welcome its widespread adoption with open arms".