More than a third of farmed fruit and vegetables never makes it on to shop shelves because it is misshapen or the wrong size, according to research.

A university study estimated that over 50 million tonnes of fresh produce grown across Europe is discarded annually, mainly because it does not meet supermarkets' and consumers' standards of how it ought to look.

In the UK, the figure stands at up to 4.5 million tonnes, the team suggests.

The research paper described food loss and waste (FLW) as "one of the great scourges of our time", when 10% of the world's population is chronically hungry.

The study was conducted by researchers at the University of Edinburgh, who examined how much food is discarded within the European Economic Area (EEA) each year before it reaches the point of sale.

Their findings stated: "The use of aesthetics for classifying and accepting fresh food for sale and consumption is built into food quality standards and regulations of the European Union.

"The food distribution sector in Europe and the UK is oligopolistic in nature; a small number of supermarket chains control a large market share. The influence of these 'multiples' enables them to impose additional proprietary 'quality' criteria.

"Produce that doesn't meet these standards may be lost from the food supply chain, never seeing a supermarket shelf - it may not get past the supplier, or even leave the farm."

The team said they found few direct measurements of such losses, but continued: "We estimate avoidable FLW from on-farm cosmetic grade-outs of up to 4,500 kt yr (4.5 million tonnes per year) in the UK and 51,500 kt yr (51.5 million tonnes per year) in the European Economic Area (EEA).

"Our estimates suggest over a third of total farm production is lost for aesthetic reasons."

The university said 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 scientists 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, perhaps in chopped or processed goods, or for sale at a discount to charities.

Professor David Reay, of the university's school of geosciences, said: "The scale of food that is wasted when it is perfectly safe to eat is shocking at a time when one tenth of the world's population is perpetually underfed."

Stephen Porter, also from the school, added: "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."

The study has been published in the Journal of Cleaner Production.