SWAYING dizzily across a rope suspension bridge, floating above the forest floor far beneath our feet, the Duchess of Northumberland and I battle on in what feels like the teeth of a gale.
It's actually a stiff breeze on a gloriously sunny afternoon, but neither of us has a head for heights. Jane Northumberland confesses that she's feeling rather sick by the time we make it to the scary glass pavement outside the turreted treehouse in the great contemporary garden she has created at Alnwick Castle.
Set amid rolling landscaped parklands, this vast and venerable ancestral pile is perhaps best known as Hogwarts in the Harry Potter films, but it is the home she shares with her husband, the 12th Duke of Northumberland, and their four children.
Alnwick's magical gardens are also the setting for The Poison Diaries, the dark and enchanting children's book she wrote recently, which has just been optioned by Hollywood - any profits will be ploughed straight back into the splendid gardens, with their state-of-the-art pavilion and visitor centre, rose garden, woodland walk, serpent garden, bamboo labyrinth, poison garden and treehouse.
She is taking me across these wild walkways, slung between a row of mature lime trees, because she wants to prove that "there's more to me than the Imelda Marcos of shrubs, which is how some people still think of me". She tells me about her plans to create a children's adventure playground underneath the treehouse - one of the largest of its kind - which will be big enough for 1,000 disabled and able-bodied children to play together. "Imagine how wonderful it is for people in wheelchairs to use this bridge - it has been designed to be safe for them. So many tell me how thrilled they are with it, since it's the only opportunity in the world for a wheelchair-user to go up through a tree canopy on suspended walkways. It's very exciting - a real paradise," she exclaims.
This ambitious playground will cost around 5 million. It is money that the charitable trust which now runs the gardens has yet to raise. Nonetheless, the lively 47-year-old is confident that they will do so. And she should know. In the past 11 years, she has created a 35 million pleasure garden that has become the biggest tourist attraction in the Borders, massively boosting the area's economy by bringing in more than half a million visitors a year. Around 100 farmers in the area have applied to create or extend bed-and-breakfast facilities, while many of the shops in Alnwick, recently voted the best place in Britain to live, have increased their takings by half.
But the duchess is not content with all that. After losing out on a Lottery grant last summer, she is about to embark on a vigorous worldwide fundraising mission to complete the project, which will cost 60 million by the time it's finished in 2008. "We'll find the money. I'm very optimistic; I have to be," she insists. The trust needs the funds, she continues, because she wants to create five more themed gardens, plant the biggest white cherry orchard in Europe and open the largest round, Christmas-tree-fringed ice-skating rink in Britain.
Up to the age of 13, the duchess was a dedicated skater, and spent most of her childhood practising at Edinburgh's Murrayfield ice rink. "I wanted to be a champion figure skater, so I would skate from 5.30am to 8am, go home to breakfast, then back to the rink at lunchtime for an hour and then another two hours after school. My parents were always busy - they had a hectic social life - so I threw myself into it," she says.
"I was given the chance of doing it professionally and going off to train in Canada, but I knew I was never going to make it. Technically, I was fine, but I was very shy. I didn't think I could conquer those fears and go out there on my own with the spotlight on me and really sell myself to the judges - you have to be very confident to do that. I am a much more confident person nowadays, though. I've had to overcome my shyness to achieve all my plans for the garden."
This may all sound like pie in the sky, but it's not where this "good Scots lass", as she describes herself - the first commoner to become Duchess of Northumberland - is concerned. There have been times, though, when her faith in the project has been shaken. "When the 2001 foot-and-mouth crisis devastated so many livelihoods in the countryside, I remember wondering if what I was doing was right," she says. "There I was, spending 5 million on a water feature, and there were farmers next door who did not know where their next meal was coming from. But it was too late. The money was spent."
Then, in 2002, the Getty Museum offered her husband 32 million for a little Raphael painting, Madonna of the Pinks. The news provoked outrage about the masterpiece leaving the country, and so the National Gallery launched a campaign to save it for the nation - although the figure couldn't be matched without Lottery money.
The Heritage Lottery Fund administrators reportedly balked "at the thought of handing over 20 million to one of Britain's richest landowners", since the Duchy of Northumberland is one of the oldest and wealthiest in the country. Its impressive art collection includes Canalettos and Titians.
In addition to the treasure-stuffed castle, the duke - Britain's 108th richest man, according to newspaper rich lists - owns the spectacular Elizabethan Syon House, on the banks of the Thames, and Burncastle Lodge, near Duns, where the family lives during the summer - when Alnwick Castle is open to visitors. The duchess, though, insists that everything she and her husband own is only "held in trust".
A noisy public debate ensued. Ironically, the Getty's "silly offer" bid of 32 million was exactly the sum Jane Northumberland had just announced was needed to finish the gardens, on which she had already spent almost 10 million. Ian August, the garden liaison officer and author of a beautifully illustrated weeds-and-all account of the construction of Alnwick's garden, remembers her saying to him, "This is horrendous. I'm going to be crucified." Indeed, she was. It made her look, said one newspaper, like "the Imelda Marcos of gardening".
The story rumbled on until 2004, when the Madonna of the Pinks was finally bought by the National Gallery for 22 million, after tax. The duke used the funds to regenerate the estates in the wake of the foot-and-mouth epidemic, and to effect vital repairs on the fabric of the castle. "The garden received not a penny," his wife asserts.
IT WAS in 1995, when her husband unexpectedly became the 12th Duke of Northumberland, that the vibrant Lady Jane Percy embarked on her grand plan to "create the mother of all attractions" at Alnwick Castle, stronghold of the Percy family since the Middle Ages. August says that she "didn't so much bring a fresh breeze as a raging gale".
Educated at Cobham Hall boarding school, in Kent, she had never expected to become a duchess. Her Old Etonian husband, Ralph George Algernon Percy, is a younger son of the Percy family. He inherited the title and lands on the death of his playboy older brother, Harry, the 11th Duke, in 1995. Harry was a keen partygoer with a passion for Hollywood. He lived at Syon House and never married, though his companions included Valerie Campbell, mother of the supermodel Naomi, and the former Bond girl Barbara Carrera. He died from an accidental overdose of amphetamines after suffering from depression.
Ralph Percy met Jane Richard at a party when she was 16 and he a year older. It was love at first sight. They married when she was 21 and have been together for 27 years. Prior to his inheritance, they were living with their four children in a Georgian farmhouse just north of Alnwick, from where Ralph managed the castle estate. When they moved into the castle, it was "a cross between a hospital and a museum, pretty sad", says the duchess, but she soon turned it into a home. Every day she would walk the dogs through the dilapidated old walled garden, which even in such a sorry state was, she says, "magical". Her husband gave her 1 million to revive the derelict 12-acre site, which has burgeoned to the point that the garden now covers more than 40 acres.
It didn't happen without criticism, though: the gardening establishment emerged from their herbaceous borders, stabbing her in the back with their venomous pruning shears. "Who knew that they could be so snobbish and so bitchy?" The grande dame of gardening writers and designers, Lady Mary Keen, accused her, in a 2003 Daily Telegraph article, of "vanity gardening". She said the duchess, who is the antithesis of the tweeds-and-pearls aristo image, "looks like Posh [Spice] in her fashionista combat cords", and that the project was full of "showbiz and razzmatazz".
But this criticism didn't dent the duchess's determination. "I dug in my heels and believed that one day people would understand what I was trying to achieve," she says. The big bonus was that the so-called 'scandal' generated an unprecedented amount of interest in the gardens. "It swelled visitor numbers enormously," she says. Despite the fact that it was still largely a building site, it became the third-most-visited garden attraction in Britain.
But all these various trials and worries led to the duchess collapsing under the mounting pressure, and being rushed to hospital. She's fine now, she says, her skin glowing, her brown eyes bright. But there were dark days, when she almost gave up. In 2004, she was on the verge of resigning from the trusteeship and giving up the garden altogether.
Her hard-living, cigar-smoking, Ferrari-driving stockbroker father, John Richard, died suddenly, and she remembers having to give a lecture about the garden a day later, to estate workers and heads of departments, as the second phase of the project was nearing completion. Not one person expressed sympathy for her loss. She felt drained and exhausted. She had faced year upon year of planning problems, money crises, vitriolic personal criticism and endless building difficulties.
She felt completely isolated. Then she was told by a member of staff, "We've got a bit of difficulty in that we never know how to refer to you and explain what you do in the garden." The duchess replied as kindly as she could, saying, "Everything you see in this garden, down to the last teaspoon in the treehouse, the candles, the lights, is a design I've chosen and worked on for the last nine years. I don't know what you call that and how you give it a job title, but that's for you to think about."
When word got round that she was close to breaking point, the castle was in an uproar. A meeting was called with the team, many of whom were in tears, after which the duchess was promised she would be widely consulted on every issue. "I just have to be plugged in at every level," she says. "The most difficult bit for me has been handing the garden over to other people to run it. I just want everything to be done properly; it's not about ownership."
Fizzing with ideas for the future of the garden, such as tea dances and speed-dating for the over-60s, she also cares passionately about Northumberland. "Most of all, though, I just can't wait for the garden to be finished next year. I can't wait."
The daughter of an enthusiastic gardener - her mother owns the famous Kailzie garden in the Borders, which are also open to the public - the duchess recalls enjoying helping out in that garden as a child. The duke, however, is no gardener. "He is not remotely interested," she says. "He can't understand how anybody could spend a whole day looking around a tamed garden landscape, especially since everywhere we go the topic of 'the garden' inevitably dominates. It drove him to distraction at one stage," she says, with a grin, adding that he has always given her immense faith and support. Theirs is a strong marriage, she says.
She's had a sweater knitted for him, with the words 'Please don't ask me about the bloody garden' emblazoned on the back. He has been known to wear it at dinner parties. "I can't tell you how many gatherings we've been to where upper-class people - dreadful expression, I hate all that class thing! - come up to my husband, raise their eyebrows and say pointedly, in front of me, 'Poor you, Ralph. I can see you've got your hands full.' Sometimes I think if I hear the words, 'Poor you, Ralph...' one more time!
"But guess what? I don't give a damn. This garden is not about me - it's about building something mind-blowingly beautiful that's going to be here in another 100 years. So who cares what they say about me!"
The Making of the Alnwick Garden, by Ian August (Pavilion, 25). The Poison Diaries, by the Duchess of Northumberland (Pavilion, 14.99). Entrance to Alnwick Garden (www.alnwickgarden.com), which is open every day except Christmas Day, costs 8 per adult, with up to four accompanying children free of charge
Life and times
Born Isobel Jane Richard in Edinburgh in 1958
Grew up in Magdala Crescent, Edinburgh
Educated at Cobham Hall boarding school, in Kent
Met her husband, Ralph Percy, when she was 16; they married in 1979
Had four children, born between 1982 and 1990
Became the Duchess of Northumberland in 1995, after the death of her brother-in-law
Began the garden project at Alnwick in 1995