ALOFT IN NATURE'S SKYSCRAPERS

TOM EAGLEHART's airy bedroom sits on a nest of timber slung between the branches of seven tall spruce trees. Roughly 30 feet above his parents' Dumfries farmland, he can hide from the world behind a curtain of whispering foliage; feel the trees bend and sway in the wind; enjoy a bird's-eye view of the Scottish countryside rolling away from his woodland eyrie down to the Solway Firth.

Tom's tree house is arranged as a stack of cantilevered platforms, connected to the ground by a ladder made from two long spruce poles. It is furnished with hammocks, a 15 tog duvet, television, video, a faded Persian rug, floor cushions and potted plants. An original Eaglehart chandelier (Tom and his father, Ed, make them from cones of fiery copperwork, hand-blown glass and beach stones) swings from his leafy ceiling. Half the living space is roofed with canvas, so he can choose between sleeping alfresco or indoors.

Friends pop up. They have parties and barbecues. On cold nights (this is is not just a summer house) Tom lights a fire in a bowl-shaped copper hearth made from the base of a defunct immersion heater. "Next, I'm planning to install a Turkish bath," he says. "Tree houses are very versatile. Anything is possible."

Twenty-three-year-old Tom says he's hooked on tree-top life. The first time he stayed the night in his "sky temple" was more than two years ago, and he hasn't come down to earth since. "Being in an ordinary house is like going back to a twilight zone - it feels so enclosed and unnatural." His parents (who live in the nearby twilight zone that connects the tree house to an electricity supply) say that it's just a phase he's going through.

Tom's "phase" might be symptomatic of late development. Perhaps he's living out a shipwreck fantasy in which the tree house is a refuge from imaginary monsters and wild beasties?

An element of escapism prevails, agrees Tom. "There is a desert-island quality about living in the tree tops." But he claims his unusual domestic arrangement is a way of "maximising the ability to be out-of-doors. I'm trying to push a concept to the limit of its possibilities."

At Selar Farm, in the Neath Valley, South Wales, a group of tree-loving environmentalists has another reason for building houses among branches. Living in a forest of ancient oaks, they are fighting to save more than 800 acres of eco-sensitive water meadow that are threatened with destruction by Celtic Energy's vast open-cast mining project. Their tree houses are fortresses, and in this adventure story the beasts below - bureaucrats, mining contractors and Department of Transport meanies in bulldozers - are all too real.

The tree house as green campaigners' weapon first emerged in 1993, when protestors against the M11 extension in east London battled to save a 250-year-old sweet chestnut tree from destruction. In the weeks before the final showdown, a well-wisher's letter was sent to the anti-road campaigners, addressed to: "The Chestnut Tree, George Green, Wanstead". The postman delivered it. And a High Court judge decreed soon after that this established the tree house as a bona fide dwelling. Eviction could not be carried out without court orders and appropriate papers. Time, therefore, was on the side of the protestors.

The move did not save the tree, but it set an important precedent, engendering the publicity which helped fire public indignation. Before its final demise, a flood of supportive mail descended on Wanstead's doomed sweet chestnut. M11 protestors later bound them into a book entitled "Dear Tree... "

Since then, whole villages of tree houses have sprung up on the frontline of Britain's anti-road war zones. In the well-documented battle to save Solsbury Hill from the advancing Bath-easton bypass, near Bath, protestors built a whole village of tree-top houses. Another grew up in the path of the M65 near Preston. Both groups slung shaky rope walkways between makeshift houses with rudimentary doors and windows. Ground-linked supply lines made the tree-dwellers self-sufficient. And when their hosts were felled, the warriors moved on to join other campaigning woodland tribes.

"The tree house thing started out as a necessity," said a spokesman for Glasgow's Pollok Freestate campaign against the M77. "Living in the trees was the only way we could defend them. But a lot of campaigners found they really enjoyed it. For some, it's become a permanent lifestyle." They all talk with enthusiasm about communing with birds and sharing mealtimes with squirrels. And their tree-house architecture has gradually become more inventive. Indeed, the tree village at Selar Farm features "family- size" tree houses that sleep 10. Wind-generated power is being installed.

In a wooded corner of the former Escot Estate, at Fairmile, near Exeter - now Department of Transport land and soon to be swallowed by a leg of the A30 improvement scheme - a veteran anti-roads campaigner called Scarlet has just put the finishing touches to her "twigloo". Basically a bent- wood dome covered in canvas and plastic to make it waterproof, the twigloo was built on the ground, pulleyed into the branches and suspended between a group of trees with rope stablisers. "It can keep five people warm and dry in the worst of weathers," says Scarlet. "But the purpose of the design is to allow one person to defend several trees at once."

Scarlet and her fellow campaigners have been camping on the anti-A30 site since October and have developed a dozen linked tree houses in copse of beech, oak, larch and sweet chestnut trees. Confrontation - followed by eviction - is inevitable and the Fairmile tribe dreams of moving to a permanent tree base.

"Living in trees changes people," says Scarlet. "When you spend a lot of time in the branches, you realise your tree is always moving - it's never still even when there's barely any wind. They are living, breathing things and each has its own personality. The trees are family to us and chopping them down is murder."

An invitation to Scarlet's twigloo meant donning ropes and harnesses and "prusiking" (a climbing term) up the straight trunk of a larch to a height of 60 foot. The return journey entailed abseiling. "It's really comfortable inside," she urged. "I've got bedding, and shelving, pictures on the walls, my collection of feathers, some red velvet covers... and my piss bottle." I could see her en suite facilities dangling from a lofty branch, but I had to take her word for the rest. I have no head for heights.

I even had my doubts about climbing the rickety log ladder up to Mark Wilkinson's magnificent tree house in rural Wiltshire, but that was a doddle compared to prusiking up a larch. And Mark's construction is purely recreational: a five-star tree house with no hint of purpose other than to entertain.

It was reading Swiss Family Robinson to his seven-year-old son, Gregory, that inspired the project. "It was wildly good fun to build," says Mark, a cabinet-maker (founder of Smallbone kitchens; now at the helm of his own bespoke furniture company). "I roped in a friend to help, and we got busy with loads of old reject planks, wheels and pulleys - the whole thing was done with hammers, nails and a chainsaw and it just evolved as we worked.

"All we had was an idea that it should look like a Tudor galleon sailing majestically through the wind - and that it should not harm the tree."

The 80-year-old ash that hosts the Wilkinson tree house had a streak of rot running through the trunk. Mark reinforced the timber with three steel props on a concrete foundation. "Without that added strength, I think, the winter gales would have felled it by now."

Inside, the timber house is lined with shiny gold cardboard ("very warm and medieval"); there are table and chairs and a stained glass panel in one of the windows; a branch of the tree grows up through the floor and out of the roof. And there's a strange feeling of distorted perspective, as though the whole thing is built at a variety of tipsy angles. It feels oddly unreal.

"The ash is traditionally the tree of healing," says Mark. "And this place does seem to have an energising effect on people." We sat for while on the galleon's poop deck - me, slightly giddy with vertigo - beneath a canopy of rustling leaves, looking out over the gentle Wiltshire fields. "It a very, very peaceful place," he added.

Young Gregory, now 13, rarely climbs the log ladder. Wilkinson Senior has colonised the nest. But surely, a tree house with microwave, refrigerator and beautifully polished Arts and Crafts-style fitted kitchen units was always intended as an adult plaything. The Swiss Family Robinson story was just an excuse. !