Estate of play: The controversial gardens at Alnwick Castle have become something of a life's work for the Duchess of Northumberland, as has the quest to fund them

The criticism I've had is just mas-sive," says the Duchess of Northumberland, as she leads a visitor through the Bamboo Labyrinth of Alnwick Garden. "It's really staggering the way that Britain views this project. They said I am to gardens what Imelda Marcos is to shoes."

Given that the project in question is, so far, a garden of 14 acres – large, but not enormous by the standards of English country estates – the duchess, 49, might seem to be laying it on a bit thick. But what she has done with these 14 acres at Alnwick Castle, her husband's ancestral home – and what she hopes to do with them in the future – has indeed stirred controversy, in worlds as diverse as the gardening establishment, parliament and the press. What started as a whim of the new duchess, who saw a chance to create a modern counterpoint to the adjacent 18th-century landscape designed by Lancelot (Capability) Brown, has become one of the most ambitious public gardens created in Europe since the Second World War, a rollicking tourist attraction widely known as the Versailles of the North. And the duchess, in her single-minded drive to make that happen, has amassed plenty of admirers, but more than a few critics as well.

The saga began in 1995, when the duchess, then 36 and known as Jane Percy, was living with her husband, Ralph, a 38-year-old property surveyor, and their four children in a farmhouse half an hour north of Alnwick. That October Ralph Percy's brother Harry, the 11th Duke of Northumberland, died. Ralph Percy was suddenly the 12th duke, with holdings that included 120,000 acres, 171 tenant farms and 700 houses and cottages, along with Alnwick Castle, with its collections of Meissen ceramics, Louis XIV furniture and paintings by Titian, Canaletto and Van Dyck. According to the Sunday Times, the duke is the 270th richest person in Britain, with a fortune estimated at 300 million.

Her husband, she says, warned her that there would be challenges. "He said, 'Don't expect to win, you've just got to do your best.' I thought, What's he talking about? He's being such a drama queen." Now, though, she sees the troubles she had with the garden as evidence he was right. "In England, if you're married to a duke and do something on this scale, it's considered to be overly ambitious," she says. "The attitude is that you should stay in your castle."

At first, she was just looking for something to do in her new role. On a walk near the castle in late 1995, she wandered through the site of the former gardens, a walled enclosure that had been planted for 40 years with spruce trees, part of a lumber business that helped support the estate. She had grown up around greenery in Scotland and had occasionally helped friends design gardens; now she began talking with her husband about reviving the gardens at Alnwick.

Even at this early stage, she wasn't thinking small: "To do anything," she told the duke, "I'm going to need a million pounds." But over the next year, her vision became grander, expanding to encompass a public garden that would draw visitors from all over the country. The duke eventually put in 8 million through his charitable trust, half in the form of a loan, and the duchess embarked on a fundraising campaign that is still ongoing.

She also became increasingly determined that the garden should be modern, not a recreation of Alnwick's long-derelict 18th and 19th-century gardens – a decision that would lead to the first of her troubles.

In 1996 she hired Jacques Wirtz, a Belgian landscape architect. Wirtz is known for a critically acclaimed redesign of the Carrousel Garden in the Tuileries in Paris, and for redoing the gardens of Elyse Palace.

He delivered a formal plan for the garden in 1997 that has been little altered since. It included prominent features of the present garden such as the Grand Cascade, a multi-tiered hillside waterfall and fountain that is the visual centrepiece of the site; a formal ornamental garden with water rills that contains one of the largest collections of European plants in Britain; a Rose Garden with 3,000 roses in 180 varieties; a Serpent Garden with swirling yew hedges and eight stainless steel water sculptures by William Pye; the Bamboo Labyrinth, with 500 bamboo plants; a 3.5 million treehouse built amid 17 lime trees, with an education centre, a restaurant which seats 80 people and thousands of square feet of suspended walkways; and the Poison Garden, a spooky fenced-off area with about 100 varieties of toxic plants, as well as cannabis and opium poppies.

Before any of this could be built, the duchess faced a challenge from English Heritage, the government agency charged with protecting England's architectural patrimony, which wanted a garden in the style of a 19th-century redesign of the original. She spent much of 1998 and 1999 and some 500,000 on research and legal fees in making her case, she says.

Other challenges came in the form of criticism of the design, particularly its populist bent. In 2003, after the first of the three phases was complete (the second was finished last year), Mary Keen, a garden designer and critic, described the place in the Daily Telegraph as "popular entertainment, the dream of a girl who looks like Posh and lives at Hogwarts".

The duchess does not take particular issue with this line of attack – "I never wanted to make a beautiful garden for elite gardeners," she says. "A lot of my ideas come from Las Vegas and Euro Disney," she says.

But the main controversy surrounding the garden has had to do with the money required to build it – its overall budget now stands at 70 million. Only two-thirds of the project, for which ground was broken in 2000, has been built so far, at a cost of 43 million, which, aside from the duke's 8 million, came from a mix of public financing and private donations.

Keen, in an article for the Spectator magazine, suggested that run-down city parks were more deserving of government help, but that the grants they get average 1.4 million, as opposed to the 3.45 million the Alnwick project had already received. "Should those who are savvier and nobler than thou," she asked, "attract so much more money than those who are apparently more deserving?".

The duchess has argued that the garden, which became a charity separate from the duke's estate in 2003, is well worth its cost to the public, as a boon to a financially troubled region with one of the highest unemployment rates in Britain. She points out that Northumberland's economic prospects were particularly bleak in 2000, the year work started on the garden.

"When I began, farmers all around here were losing their livelihoods," the duchess says, referring to that year's epidemic of foot-and-mouth disease. "And here was I at that stage, spending 5 million to build a cascade. I remember thinking, how can I be doing this? I felt like Marie Antoinette."

"What I didn't realise," she continues, "was that the garden would become a focus for regeneration. Those farmers' wives were baking for the tearoom here." In one year alone, she says, 100 farmers and other locals applied for planning permission to turn their houses and outbuildings into B&Bs.

According to Ian August, her longtime aide, of 100 local businesses to which a questionnaire was sent, 59 responded, saying they had developed and expanded as a result of the garden.

The garden has certainly outperformed the expectations of a feasibility study conducted by KPMG, the accounting firm, in 1997, which estimated it would attract 67,000 visitors a year – only slightly more than the number of ticket buyers who toured the castle at the time. During its first full year of operation, the garden had 330,000 visitors, and by last year the number had jumped to 625,000.

The garden generates up to 53 million in extra spending for her district, the duchess says. (The increase in visitors may also have something to do with Alnwick Castle being used as a location for Hogwarts in two of the Harry Potter movies. And there is general acknowledgment that Alnwick's economy was boosted by Country Life magazine's 2002 selection of the town as the best place to live in Britain.)

August says that when the third phase is complete the garden is expected to create as many as 445 jobs. That final phase includes five new gardens; a huge lighting programme; an ice rink that would become a pond during summer months; and a 4.5 million playground with an obstacle course designed to be used by both children and disabled adults. The only hitch is that the duchess still has to raise 30 million.

Speaking of this endless quest, the duchess says: "My husband said, 'Can you do this? At what price? Will it kill you?' I said I have to."

"I never for a second think I won't finish the garden," she added. "But I just don't quite know how." sm

n The Alnwick Garden is open daily, except Christmas Day. Adults 10/7.50; children under 16, 0.01. Visit www.alnwickgarden.com for more information.