More than a third of farmed fruit and vegetables never reaches supermarket shelves because it is misshapen or the wrong size, research suggests.

A University of Edinburgh study found more than 50 million tonnes of fruit and vegetables grown across Europe were discarded each year.

This was in part because they did not meet supermarkets and consumers' standards of how they should look.

The climate change impact of growing the wasted food – some of which may be ploughed back into fields, used in animal feed or otherwise reused – is equivalent to the carbon emissions of almost 400,000 cars.

The study was published in the Journal of Cleaner Production.

The researchers examined details of food loss and waste within the European Economic Area and studied how much food was discarded each year before it reached the point of being sold.

The researchers attributed losses to strict government regulations, supermarkets' high standards as well as customer expectations of how produce should look.

They also found that farmers contracted to supermarkets typically grew more food than they were obliged to supply, to allow for a proportion that would not be deemed fit to sell.

Researchers suggest that greater awareness among consumers, and a movement towards shopping sustainably, could encourage the sale of more ugly vegetables. 

They also suggest a greater use of misshapen produce, for example in chopped, processed or picked goods, or for sale at a discount to charities.

Stephen Porter, of the University of Edinburgh's School of GeoSciences, said: "Encouraging people to be less picky about how their fruit and vegetables look could go a long way to cutting waste, reducing the impact of food production on the climate, and easing the food supply chain."

In recent times, UK supermarkets have been making more space for increasing amounts of less-than-perfect produce.

Last year, Sainsbury started a campaign to encourage use of blemished bananas, while Morrisons introduced a new "wonky" range that included avocados.

Others, including Waitrose, Tesco and Asda, also branched out into selling misshapen fresh items.