The Soil Association (SA) has called on processors and retailers to source more UK organic ingredients and products, especially fruit, vegetables, meat and fish.
Its latest Organic Food & Farming Report said that while sales of organic food have increased by 10% over the past year to £1.12bn, 56% of products are still imported.
One fifth of organic meat sold in the UK is from overseas, while organic potatoes, carrots, onions, apples and pears come from abroad even when in season here.
Michael Green, the report's author, said manufacturers and retailers had to change their buying policy to ensure sustainability of the organic market.
"Sustainability cannot be achieved by changing farming alone, we must change market structures, too," he said. "A healthy organic future cannot be sustained by high levels of imports of in-season fruit and vegetables and meat."
Meanwhile, the amount of UK land used for organic production fell by 5% from 726,400 hectares in 2003 to 688,373 hectares as farmers left the sector. This year also saw a 70% fall in land being converted to organic status. The proportion of organic food sold through supermarkets also fell by 1% for the second year running.
Helen Browning, the SA's food and farming director, called on producers to create more branded organic products.