'Everyone should have the opportunity to be 12 again,' chuckles the air- traffic controller, slithering through stinking mud in the slipstream of his tiny wife, her large, floppy brown ears denoting her status as the human 'hare'. The couple are engaged in 'hashing', a British colonial invention that has captured the imagination of the world.

More than 50 years after hashing was invented, young children, the elderly, serious runners and even the positively unfit are galloping their way through deepest Wiltshire woodland to the sound of a hunting horn and delighted shouts of 'On] On]'

The sighting of another blob of blue, speckled sawdust signals to the pack of 80 Wessex Hash House Harriers that they are hot on the trail of the three 'hares'. When they approach the edge of a village, three elderly locals are standing on the other side of a hedge, like a serried rank of runner beans, looking askance at this trickle of noisy, mud-spattered folk, passing by in all manner of dress.

A piece of blue tape strung from a gatepost has one rookie asking if this is a misleading clue for a false trail. 'More likely last night's knicker elastic,' grins Gordon Raggett, a second-hand car dealer who holds the title of Grand Master of the Wessex Harriers, one of the largest family hashes among the 93 registered clubs in the UK.

A retired banker leaps over a fresh cowpat (this is 'high grade shiggy' to hashers), and an estate agent and his family wade knee-deep through a smelly stream. This 'classless gathering of equals enjoying a mind-rinse', in the words of their Grand Master, probably bears little resemblance to the rather more dignified, gentlemanly concept of the original running club established by expatriates in Kuala Lumpur in the late Thirties.

The idea of 'hares' laying a trail through the back of beyond for a pack of human 'hounds' was a way of relieving the boredom of colonial life in Malaya for a handful of men who would meet at the Selangor Club. Nicknamed the Hash House, because of its institutionalised food, the club formed the base for a pastime involving running, a few cold beers during the recovery period, as well as an addictive jollity.

There are now more than a thousand registered clubs of Hash House Harriers, with Malaysia and America leading the field, from jungly undergrowth, to sun-bleached mountain tracks beyond the Costa del Sol, to Moscow's Gorky Park, where embassy staff were once arrested by mystified Russians.

In deepest Wessex, however, this madcap joviality is a family affair, although with no less fun as a result. Guy Reynolds, 12, from Dorset, has been charging across buttercup fields and bounding over fallen tree trunks with his parents since he was two weeks old. 'It's a lot of laughs and it keeps you fit. You also get to talk about things,' he explains, briefly disappearing among the towering rhododendron bushes. 'There are a few soldiers in this Hash and I like listening to their stories.'

Alan Reynolds, a property man, recalls how, a few years ago, his son's quick thinking calmed an irate colonel who had emerged from a block of retirement flats as the Wessex Hash shattered the Sunday morning peace of suburban Bournemouth. Noisy laughter and enthusiastic shouts of 'On] On]' had him bristling with rage. 'What the hell is going on?' he bellowed. The child explained that he had a dog called On-On which had run off. 'At which point,' says Alan, 'the colonel seemed genuinely upset and briefly joined the so- called search party.'

But enough of the anecdotes. The serious runners are ahead now, on a six-mile trail that took three weeks to plan, and includes a mini-version of four miles for the less dedicated and those like myself who are normally left puffed and gasping after a trip to the local post office.

Hilary Gallop, her floppy brown ears now drooping to her shoulders, waves us towards a white iron kissing gate on the edge of a private wood that required written permission from the owner to enter. The sawdust trail remains carefully marked out from the day before. The route is planned and walked by the 'hares' in advance, and today includes stagnant water and thick mud, as well as dips and gulleys guaranteed to put every unsuspecting muscle to the test.

The minute blue bits of paper that make the sawdust clues more visible are the only element of hashing which appears to have caused environmental angst. 'People have come out and scraped it away thinking it was rat poison,' says Phil Davies, at 82 the oldest member of the Wessex Hash.

After newspaper headlines splashed 'Dog killers on the loose', one Dorset council spent pounds 65 on having the sawdust analysed. 'They're just bits of blue parking tickets from Poole,' laughs Cindy Wedlake.

They are biodegradable, of course, part of the responsible attitude that hashing takes to the country code.

'We always walk round the edge of fields containing crops,' says Mr Raggett. 'Gates are closed behind us, and in 99 per cent of cases we let the farmers know we're coming, or ask permission if appropriate.'

Keith Hawkins, a Hampshire lawyer, delights in the opportunity to explore pockets of English countryside that he would never otherwise have bothered to visit. 'You also get right away from the stresses and strains of everyday life, wear what you like, behave as childishly as you like and it simply doesn't matter.'

As he breaks into a trot to cross a track into a nearby wood, Lucy, the Yorkshire terrier, overtakes on the offside. Along with the other assortment of large and small dogs, struggling with their owners on the ends of leads, Lucy's wagging tail indicates that she, too, revels in the camaraderie that hashing engenders.

Somewhere in the distance, the ubiquitous cries of 'On] On]' can still be heard. Yet as rapidly as these people and their dogs emerge out of the sunlight flickering through from the trees above, all but one is just as quickly gone again.

'It's one of the mysteries of hashing,' explains Mr Reynolds as we squelch past wild orchids and wooden deer lookouts. 'You can be running along with a whole lot of others and suddenly find you're in a wood completely on your own and you can't understand how it's happened.' As we pause, the stillness of the day is punctuated only by the throaty sound of a wood pigeon.

Occasionally couples enjoying some peace in the middle of their chosen sanctuary can find themselves exposed to advancing bands of cavorting hashers, running towards them from all directions through the trees with those gleeful shouts of 'On] On' as they go.

While many are attracted by the high spirits and camaraderie, others find hashing a therapeutic exercise. 'By the time you get to 40, most people have had something bad happen in their lives,' says a chartered engineer, negotiating another stile on the final stretch back to the pub. 'This is a way of getting rid of the rubbish.'

Phil Davies, a retired telephone engineer who didn't start running until he was 75 and has two London marathons to his credit, says that hashing changed his life. 'It's a great leveller. We've got all sorts in the Wessex Hash, from taxi drivers to barristers, out-of-work labourers to ambassadors. But we're all one. It's totally classless and I've made friends with people I would never normally meet.'

One wife confided in Phil how delighted she was that her businessman husband could enjoy such a relaxing activity. 'When he came home from work, his level of tension made the whole house uptight. After hashing, she said, the release for him meant that they were all relaxed.'

There is certainly no pressure to perform or compete, which many find appealing. The trails are so arranged that the serious, fit runners can go as fast as they like, while people who are absolute amateurs can walk or run at their own pace and still finish at the same time.

'For many blokes, other sports - like golf, for example - are simply an extension of the work ethic. They're still out to prove that they're the best man,' Mike Lynch observes, emerging soaked to the skin from a hedgerow into the road leading to the village and the scent of real ale. 'This is full of fun and totally relaxing. No one feels they have to prove anything at all.'

The Wessex Hash House Harriers describe themselves as 'an extended family' in which anyone can find 'a sense of belonging'. Looking perky after his four-mile round trip, young Jonathan Skinner puts it in perspective as he scampers up behind us holding his mum's hand: 'I like all the mud]' So do the adults.

'As I said,' murmurs Mr Raggett, the Grand Master, reaching for a well-deserved pint of best bitter, 'hashing is a total mind-rinse.'

(Photographs omitted)