In the period covered by the survey, less than a quarter of the organic pork on sale in Asda was from UK farms; in Tesco only half the pork and under half the organic beef was from the UK. Only 13% of Safeway’s cauliflowers were homegrown, and in Asda only 19% of onions were homegrown.

In the UK, farmers producing organic pork must meet high animal welfare standards, which is not always the case in other countries, the Soil Association warned. 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.

However, the Soil Association’s survey found that UK sourcing is possible: 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% of beef and pork from UK farmers, and Marks & Spencer achieved 95% with beef. Waitrose achieved 99% UK-sourced potatoes.

Peter Melchett, the Soil Association’s policy director singled out Waitrose, Sainsbury’s and Marks & Spencer for praise but said that some supermarkets were letting down 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,” Melchett said.