Half of farmers questioned by Friends of the Earth feel trading conditions with supermarkets have worsened.

FoE sent questionnaires to 100 farmers in order to get evidence for the Competition Commission inquiry.

Just over a third responded to the survey, which asked such questions as whether farmers had ever been asked to meet the cost of a buyer's forecasting error or for a retrospective price reduction.

"When asked if things had changed over the past couple of years, around half feel things have got worse," a spokesman said.

"Around a third said they were receiving the same or less than the cost of the product."