Britain was short of 5,130 migrant workers on farms in July, according to an NFU survey of labour providers - causing major problems at harvest time.

Farmers and growers needed 48% more workers from EU countries and 3% more through the Seasonal Agricultural Workers Scheme, the findings showed - 20% more overall.

The situation is set to worsen next year, the NFU has warned, as it becomes harder to recruit workers from increasingly affluent A8 Eastern European countries. And changes to SAWS will stop the flow of workers from outside the EU.

"This year we were allowed 16,250 students from Europe and farther afield under SAWS," said Philip Hudson, NFU horticulture adviser. "But the Home Office says 100% of that quota must come from Romania and Bulgaria in 2008 - something gangmasters will struggle with."

The NFU is calling on the Home Office to reverse its decision, and has promised further labour surveys.