It was a beautiful onion, anybody could see that – a good, healthy size and dried to a perfect even colour. Medwyn Williams, the village show’s judge, spotted its prize-winning potential at once – until he picked it up, that is. “There was a clunk as something dropped to the floor,” he says. “So I had a look at the onion and there was a great hole in the bottom. It had been filled with Polyfilla.”

This time of year is the height of the vegetable showing season. Across the country, in marquees, village halls and working men’s clubs, the nation’s garden produce is being set out for judging. Just occasionally, though, some of us can get a little carried away. Without putting too fine a point on it, we cheat.

“A lot of gamesmanship goes on,” admits Williams, chairman of the National Vegetable Society. “When a cucumber flower drops off, it’s not unknown for somebody to stick it back on with superglue. People stick florets onto cauliflowers, and I’ve seen an old chap trying to cover up a mark on a pea with a green felt-tip pen.” Judges are also on the lookout for marks on apples showing where the supermarket label has been peeled off.

You don’t find this sort of thing at a national level, but anything goes when it comes to the village show. Williams, who has won 10 gold medals at Chelsea, remembers judging a show near his home in Anglesey, north Wales. “When I came to the carrots, I could smell something,” he says. “I couldn’t work out what the hell it was, but when I handled one carrot, my hand went straight into a small crack. The crack had been filled with Mansion floor polish.”

Mine’s bigger than yours

It’s shovels at dawn at the village hall, as the vegetable showing season reaches its peak

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• Vegging Out: how to start a vegetable patch

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Background

• Salad days that last forever

• Grow your own meals

• Dolce vita on a plate

• Go ahead, pack it in

• Seeds of change

Nowhere is the competition hotter than in the dog-eat-dog world of leek shows. Just ask David Evans, 40, a groundsman from Leadgate, in Co Durham, and vice-chairman of a show at a local working men’s club. By rights, he should be in celebratory mood: his latest crop of leeks had pearly white roots the size of a man’s head, making them certain winners. Which meant they had to go.

An unknown saboteur crept onto Evans’s plot in the dead of night, armed with a kitchen knife, pulled the leeks from the ground and split them from the root to the tip. “They were the best ones I’d ever grown,” Evans says. “I think they’d have had a chance of breaking the show record.”

Sabotage is more common than you might think. In 2001, two growers had their leeks attacked at Haltwhistle, Northumberland, for the second time in two years. That same year, former local show champion Derek Fisher’s crop was doused with toilet cleaner in West Denton, Newcastle.

For the leek-growers of northeast England, in particular, the show season is not just about pride – it is about money. Most villages or small towns have pot-leek clubs, where first place can win up to £1,000. The prizes on offer make the competition so intense, some judges refuse even to travel north. “It was so bad when I was up there, they had Securicor patrolling the allotment sites a couple of weeks before the show,” says Rob Foster, gardening expert at Radio Mansfield. “Instead of staying after the show to give advice, the judges had to go before the competitors came back into the marquee, because sometimes fists started flying.”

The leek competitions date to the late 19th century, when miners began organising shows in clubs and pubs, paying a little each week to fund prizes. Things have now become so serious that some exhibitors spend the night out with their vegetables to guard against intruders. A former chairman of the National Pot Leek Society once remarked: “At the height of the showing season, some men really do sleep with their leeks more often than they do with their wives.”

All this makes Wallace & Gromit in the Curse of the Were-Rabbit – in which the Plasticine duo are hired to guard vegetables before a big show – look like a true-life documentary. The obsessive nature of leek-growing was the subject of King Leek, a television comedy shown in 1996. In it, Tim Healy played an ex-miner so confident of winning a show, he stakes the family home on it. “When I started looking into the passions growing pot leeks arouses in some men, I was surprised,” said William Ivory, who wrote the script. “Obsessive growers get so involved in the welfare of their leeks, it’s like a love affair.”

In the rest of the country, where you are more likely to win a modest cup than £1,000, the rivalry is friendlier. But there are still people who stretch the rules to the limit – if not beyond.

Simon Smith, 43, a sales manager from Loughborough, was a rookie exhibitor when he learnt the hard way. “An old boy in my area used to try the odd trick with newcomers,” he says. “I remember showing a pair of large cabbages next to his. He picked mine up and took off some of the outer leaves, under the pretence that it would make them look better. I stopped him before he went too far, and won the class. It wasn’t unknown for him to ‘accidentally’ knock the flowers off cucumbers. You soon learnt you had to watch him like a hawk.”

Cucumber-growers might be spared this worry before long. The Royal Horticultural Society is reviewing its rules on vegetable showing. In future, prize-winning cucumbers might well be shown naked – without their flowers.

Some people, though, will always find a way around the rules. “I know of two growers who, allegedly, buy all their produce at the after-show auction, then enter it into another show the next day as their own stuff,” says Smith, author of the Vegetable Grower weblog (smithyveg.blogspot.com). “Quite what satisfaction they can get from this is anyone’s guess.”

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