The Association, which promotes the UK organic food industry, claims that Tesco, Asda and Safeway are all importing substantial amounts of organic food rather than buying from UK farmers, even when UK supplies are available - a far cry from the high level of support for British farmers claimed by most of the leading supermarket groups.
According to a survey carried out by the Soil Association, less than a quarter of the organic pork on sale in Asda was from UK farms, while in Tesco only half the pork and under half the organic beef was British. Only 13 per cent of Safeway's cauliflowers were home-grown, and in Asda only 19 per cent of onions.
But there is more than a simple desire to promote British farmers behind the Association's claims. "In the UK, farmers producing organic pork must meet high animal welfare standards, which is not always the case in other countries," the Association said in a statement.
"All imported organic food must meet European organic legal requirements, but for some products such as pork, these may be lower than the standards required of organic pork reared in the UK. Some EU countries allow pigs that have lived nearly half their lives indoors, and have been bred from non-organic parents, to be sold as organic."
The Soil Association said it had written to both Tesco and Asda asking whether they can assure their customers that their imported organic beef and pork is produced to the same high animal welfare and environmental standards as beef and pork from animals reared in the UK.
The survey not only raises questions over the harmonisation of European organic rules - why are some countries' rules more stringent than others, for example, and should this be made clearer on food labels? - but also over the sourcing policies of Britain's leading supermarket chains, most of which go to great length to stress their credentials as supporters of UK farmers.
Sourcing from other European markets would be more acceptable if there was a clear gap in the UK supply market for these products, but the Soil Associaiton suggests that 100 per cent of supermarkets' organic food requirements could be met by UK producers.
"In Waitrose, all organic carrots, chicken, beef and pork were home produced, as was all the organic beef and pork in Safeway. In Marks & Spencer all organic carrots were from the UK. Sainsbury's managed to source 96 per cent of beef and pork from UK farmers, and Marks & Spencer achieved 95 per cent with beef. Waitrose achieved 99 per cent UK-sourced potatoes," the Association said.
Nearly 1,000 shoppers around the country visited their local supermarkets to find out what percentage of staple organic vegetables and meat on sale were produced in the UK. All these products were in season at the time (mid-November to mid-December 2003) and readily available from UK organic farmers. Peter Melchett, the Soil Association's policy director, praised those retailers with a strong British organic food offering. "We congratulate Waitrose, Sainsbury's and Marks & Spencer on their achievements, but some supermarkets are letting down their customers and UK organic farmers.
"It is unacceptable for staple foods like cauliflowers and carrots to be imported when they are in season in the UK, and in plentiful supply. Buying British organic food supports British farmers, guarantees the highest standards of animal welfare and helps British wildlife thrive. It also cuts down unnecessary food miles, reducing pollution and climate gas emissions."
He also highlighted the importance to the burgeoning organic food sector of maintaining its quality image - one of the key drivers of the market and one of the main justifications for the premium price charged for organic food - and the threat to this image from increasing imports from the Continent.
"All organic consumers value the high standards of animal welfare and environmental stewardship inherent in fully organic systems, and we believe Tesco and Asda customers have a right to know if these standards are not being met when they buy imported organic meat," said Melchett.
The British government has thrown its weight behind the sector, setting a target of 70 per cent UK-sourced organic food by 2010, and the Soil Association has called on Ben Bradshaw, the minister responsible for organic food and farming, to raise these results with Tesco, Asda and Safeway.
In fact, the survey's results showed that none of the supermarkets were consistently good or bad when it came to sourcing their organic foods. For example, Waitrose only managed to source 41 per cent of its organic onions from the UK (the third best performance), while Sainsbury's achieved 23 per cent.
Marks & Spencer did worse than any other supermarket in the survey with potatoes (58 per cent, while Tesco was the second best on chicken (96 per cent). As well as sourcing 100 per cent UK pork and beef, Safeway was third best on potatoes, and Asda sourced 96 per cent of its carrots from the UK.
The importance of sourcing food from British farmers is underlined by a recent survey from grocery sector think tank IGD, which showed that 56 per cent of consumers in the UK would buy British food (organic or otherwise) if it were available. But the survey also showed that 30 per cent said that they would do so only if the food were cheaper or better quality than equivalent items sourced elsewhere - underlining the need to maintain the highest quality standards for organic produce.