This is not remotely a book about food; we'd better make that clear at the outset. The vegetable freaks whose biographies Leapman meticulously compiles are variously described as “monstrous”, “grotesque”, “misshapen” and “tasteless”.

The biggest beetroot in the world, it seems, is so tough and fibrous that it is fit only for chopping up and feeding to cattle. Yet growing it - along with jumbo versions of pretty well every other vegetable in the seed catalogue - is the obsession of a growing number of gardeners across Britain.

Each year they turn up at the autumn shows struggling under the weight of outsized marrows, or desperately trying to avoid injury to the stretched-out carrot that's three times the length of Alan Titchmarsh. They'll have spent the best part of a year cosseting these overindulged horrors. And even if they pick up a string of first prizes, they will still walk away with only a few pounds in their pockets.

But this isn't about money. These men - and unsurprisingly they are mostly men - are sportsmen. They are competitors in what they like to think of as the extreme sport of giant vegetable growing. It's enough to see their charges up there on the winner's rostrum as the biggest, the longest, the heaviest or whatever. And there's always the chance they will pick up the greatest of all prizes - the equivalent of Olympic gold in the giant vegetable world - an entry in The Guiness Book of Records.

At one level the whole thing's so ludicrous it's easy to see these characters as no more than harmless British eccentrics. But I have to admit that by the time I'd finished this fascinating book I had a real respect for them. There's something heroic in this single-minded pursuit of the superlative.

All right, so it's not the 110m hurdles or the cycling pursuits. But growing Britain's heaviest pumpkin takes the same kind of dedication, believe me. What's more, it's a competition that could be said to be truly democratic. This is a sport for the average working guy, not some coddled elite.

Leapman guides us through this strange world by shadowing a group of its key players through a season as they prepare for the 2007 shows. While displaying the total commitment of all top athletes, the stars of the Big Veg league each have their own individual techniques.

Gerald Treweek, a retired coal miner, raises his world-beating onions by hydroponics - nutrient solution. They don't grow in soil but on an artificial medium in tanks. Every so often they're flooded with nutrient-enriched water, then allowed to dry out before the next dousing.

Peter Glazebrook, a former buildings surveyor, grows his onions perched on top of compost-filled barrels, their stems supported by a home-made structure built from bamboo and rubber rings. Joe Atherton, who works in a plant nursery, grows elongated carrots in lengths of guttering fixed at an angle of 45 degrees.

Clive Bevan raises his long cucumbers inside women's tights. Apparently this allows them to expand in all directions. When raised in the more traditional sock they're liable to touch the end, lose heart and stop growing.

Ian Neale - a nursery owner who once grew the world's biggest beetroot at 51lb 9oz (there is no metric system in the world of giant veg) - gets his monsters off to a good start by feeding them rock dust, essence of pig slurry and a material called “dinosaur fertiliser”, from a “big pile on the top of a moor in Yorkshire”.

Whether any of this stuff works is beyond me. It seems to be as much a matter of luck and the season. Thanks to heavy rains, many giant veg growers considered 2007 to be one of the most difficult seasons ever.

But at Shepton Mallet - venue of the National Amateur Gardening Show - Joe Atherton beat the world records for longest carrot and heaviest parsnip. That's showbusiness for you.

The Biggest Beetroot in the World: Giant Vegetables and the People Who Grow Them by Michael Leapman
Aurum, £14.99; 267pp Buy the book here

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