Growers are being hit by rules that can, for example, require potatoes to pass a skin-brightness test, apples to undergo a crispness examination and carrots to be straight and clean-shaven of all root hairs.

These are just some of the hundreds of regulations drawn up by supermarkets as they compete to offer customers the glossiest, best-shaped and most luscious-looking fruit and vegetables.

The result, according to research by the Soil Association, is that between 25% and 40% of most British-grown fruit and vegetable crops are being rejected by the supermarkets. Although some is resold to the catering trade, food processors or as animal feed, much of it is thrown away.

Patrick Holden, director of the Soil Association, said: “The supermarkets want food that looks like it never came out of the ground. Much of it is purely cosmetic — farmers are being driven out of business simply because of natural skin blemishes or slightly odd shapes.”

Supermarkets say they have little control because they have to follow consumer trends.

Each year, however, they issue farmers and food packers with lengthy specifications for each of the fresh fruit and vegetables they want supplied. One such document, issued by Somerfield, sets out its criteria for cauliflowers over three pages, including a demand that all should be 12cm-16cm and uniform in colour with no more than two spots per leaf.

It also lists a host of other demands, including one that all cauliflowers must be at exactly 6C when they are delivered to the store’s depot.

One farmer, who requested anonymity, reported how Tesco had tested his potatoes with a “brightness meter”, to see if their skin was shiny enough.

“Potatoes come out of the ground and a little dirt preserves the flavour and stops them drying out,” he said. “They want vegetables that look man-made.”

A Kent apple grower described how his products had been examined by a supermarket with a “crispmeter” to see if their flesh was firm enough. “Apples should be crisp but flavour is important too,” he said. “The result of all these demands is that supermarkets are making our fruit and vegetables all look exactly the same, all year round and all over the country.”

Geoffrey Philpott, who grows cauliflowers, in Kent, said: “The supermarkets make slight changes in the specifications all the time. The rules are now so tight that we don’t even bother harvesting about 20% of our crop. Then we lose at least another 10% during processing, plus some more gets sent back from the packers for being substandard.”

William Chase, a potato grower from Herefordshire, believes the obsession with vegetables of attractive appearance means consumers are offered good-looking but tasteless varieties. “I stopped supplying supermarkets and founded a crisp factory,” he said. His Tyrrells brand sells across the country.

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