Over the past eight years, Phil Muil has built more than 50 tree houses, and no two have been the same. He has made simple platforms a few feet above the ground and luxurious summer houses high up in the branches with the squirrels and woodpeckers; kids' play areas with rope bridges, slides, and scramble nets and peaceful retreats for adults who need to get away from it all.

Some of his designs are geometric - hexagonal, or with crenellations. Others owe their inspiration to Middle Earth and Harry Potter, with gothic windows, hand-carved doors, and secret tunnels.

They are all designed on site, to complement the chosen tree and its surrounding environment. Sometimes new ideas emerge during construction.

Mr Muil explained: "It's the most amazing part of the project, building the platform, and then thinking: We could do a rope bridge to that other tree, or a zip wire', or you might see where there's a perfect place for another platform."

He works closely with the client to come up with a design that will suit them, before producing a detailed plan and fixed quote. For example, if they want a tree house for their children, it may be possible to fit it into a tucked away corner of the garden that would otherwise be dead space', ensuring some peace and quiet for the adults.

He added: "You can really enhance the environment, and make what's there much better."

Mr Muil believes that today many children spend too much time closeted indoors and would benefit greatly from more outdoor play.

"Kids learn through tactile contact, by interacting with the tree, different finishes of wood, the ropes and the poles. You can take them as close to nature as possible," he said.

But tree houses are certainly not just for children - they can be places for adults to work in or relax, too.

Mr Muil teaches T'ai Chi and practices meditation, and several projects he has built have been intended for use as meditation spaces.

All types of tree can inspire a tree house, from an old, gnarled apple tree to a magnificent oak in its prime, but he does have a favourite.

He said: "Beeches are beautiful. The bark is so velvety and gives such a good grip when you climb it."

His knowledge of the growth patterns of trees influences the design. For example, a mature oak will grow around one inch in radius every eight years, and a platform can be built in such a way that it can be gradually widened and not constrict the trunk.

Even apparently unsuitable trees may have potential, given an appropriate design.

Mr Muil has built a free-standing tree house around an elder tree which would not have taken its weight, and others where sturdy poles and strong ropes have actually helped to strengthen the tree.

Particular care has to be taken with horse-chestnuts, which have a tendency to shed branches, and with trees on water-logged soil. If the client has safety concerns, he can put them in touch with a tree surgeon.

About 90 per cent of the wood he uses is larch, from Eynsham Sawmills, which sources all its larch from the UK.

He said: "It's the most amazing wood - half way between pine and oak, and very long-lasting - it's what they used to build ships with. And I really like the idea of materials being local."

Despite the snakes Mr Muil's interest in encouraging adventurous and imaginative play stems partly from his own outdoor childhood in Natal, South Africa.

He explained: "Growing up there was much more like an old-fashioned childhood here. We nailed together go-karts out of old pram wheels, and built tree houses and a den under my mother's vegetable patch - despite the snakes!"

He came to the UK in 1980, when he was 14. His family had decided to leave South Africa because of the political situation.

Mr Muil studied mechanical and electrical engineering at technical college, but his skills are largely self-taught, developed from a natural talent for practical things like carpentry, welding, and plumbing.

His first commission for a tree house came in 1998, through a family connection, from Railway Children actress Jenny Agutter.

She asked him to build a shipwreck survivor's hut' up in her garden overlooking the Lizard in Cornwall, for herself, and another tree platform for her children to play on.

Since then, commissions have come by word-of-mouth, advertising in magazines and newsagents, and his website.

His work has also been featured in the book Ultimate Treehouses by David Clark (Salamander, 2003).

The price of a tree house ranges from £1,500 to £25,000, but he prefers doing smaller-scale projects, because they offer more flexibility. He only takes on one job at a time and loves visiting a new site for the first time.

He said: "It's such a special feeling. You're by a tree, on the ground - and you're about to create a whole new world."

n Contact: Phil Muil, 07711 573750, or see www.wildwoodtreehouses.co.uk