It said the very hot weather was creating a short picking season that might deplete frozen vegetable supplies.

Continental crisis

The heatwave has also raised the spectre of forest fires in Central Europe, adding to farmers' concerns.

In the UK the Processed Vegetable Growers' Association (PVGA) forecasts price rises and shortages as the extreme weather bites into harvests.

The PVGA predicted that yields of peas, broad beans, cauliflower and spinach could drop by 20%.

But the fears were contradicted by Sainsbury's, which remains confident that it can keep its stores full of fresh produce.

Don't panic

"This is a bit of a storm in a vegetable basket and we do not envisage any shortage," a Sainsbury's spokeswoman said.

She pointed out that the season for some greens was coming to an end in the UK, and other vegetables - such as carrots or potatoes - were in plentiful supply.

While Sainsbury's has a policy of sourcing food from the UK whenever possible, it does import vegetables from overseas, meaning that supermarket shelves are less vulnerable to local factors.

Fears that the very hot weather will disrupt vegetable supplies stems from the way each line of produce is managed on the farm.

Crops are planted so that each field is ready to be harvested at different times, allowing vegetable pickers to keep up a steady supply throughout the season.

Very hot weather has wrecked this schedule and left farmers scrambling to bring in crops before they spoil, according to the PVGA.