The Soil Association says the big chains must import less

The Soil Association, which represents organic farmers, says the big chains are getting vegetables from abroad even when they were in season in the UK.

Supermarkets import between 70% and 80% of their onions, a survey for the association found.

And 23% of organic pork at Asda, and 50% at Tesco, was also imported.

The Soil Association was particularly concerned about organic pork being imported because it believes welfare standards in its production is worse in some other countries.

The association's marketing director, Martin Cottingham, said that, while the supermarkets must do better, there have been some recent improvements.

He told the BBC: "Just two years ago, only 30% of organic food was coming from the UK and now it's nearly 50%.

"That's partly a reflection of the government's organic action plan two years ago which has really nudged things in a positive direction."

'Customer demand'

The government has said by 2010 it would like to see 70% of organic food sold produced in the UK.

Mr Cottingham singled out Asda and Tesco as chains with improvements to make in certain categories of organic food.

A spokesman for Asda said 90% of the food sold at their stores "that can be sourced from Britain is sourced from Britain".

And a spokeswoman for Tesco said it worked hard to increase the amount of organic products sourced from the UK.