Five years ago, a caretaker-cum-handy man for Hampton Court, in Herefordshire, thought how marvellous it would be to create a dazzling garden in the estate's extensive grounds and then open it to the public. Next weekend, on midsummer day, the 20-acre park and gardens he envisaged will become a reality. Just now 18 craftsmen are putting the finishing touches to one of the most ambitious privately funded gardens to be built in this country in the past 30 years.

"I went to my boss with the idea and he came up with enough money to pay a designer for a scheme," says Ed Waghorn,. the 37-year-old former caretaker.

Within months of outlining his grand plan, he was elevated to estate manager and entrusted with the task of restoring the 15th-century castellated house as well as ensuring that the garden was completed on time.

His first job was to find a designer. Bryan's Ground, a nearby garden created by Simon Dorrell, the designer of the magazine Hortus, and his partner David Wheeler, caught Waghorn's eye.

Dorrell came up with a grand plan embracing canals, avenues, flying hedges, cascades, parterres, sunken garden and - reluctantly - a maze. The maze was Waghorn's idea and he presented the finished design to the Van Kampen family, the publicity shy American benefactors who own Hampton Court and hope it will become a Christian Centre.

They said "yes". No quibbles. Just "yes".

"Now I am carrying a dream forward," says Waghorn, whose scheme has diverted most of those working on the house to the garden for the past couple of years.

Unlike Jane Northumberland's extravagant scheme at Ainwick, where designers were brought in from Belgium and contractors from outside, Hampton's garden was to be made by craftsman already working on the restoration of the house.

Every stage of the project has been monitored by the Van Kampens but no overall budget was set. Each stage was assessed and agreed on its own merits.

"I do not know how much it has cost and I do not want to know. But we hope the garden will become self-supporting once it is open," says Waghorn. He lives on the estate with his wife Rowena. who is expecting their fourth child.

The low tunnel of grand old wisterias leads from the huge open apron of land around the house into two walled kitchen gardens. The first is now an ornamental garden. The further garden, now a haven for dandelions, is destined to be productive and fully organic by next year.

"That was the idea of Steve Coone, the head gardener. That is the thing about working here, the Van Kampens want peoples input and they want them to be involved," said Waghorn.

In the first one-acre walled garden two hardwood, stone and brick octagonal pavilions are being constructed at the centre of two stone-edged ponds filled by water from a stepped stone rill.

Outside the high mellow-brick walls is an ingenious, six-sided, stone-clad steel construction, invented by Waghorn, which distributes the water throughout the garden. This involves water power and a system designed by Hampton Court's l9th-century owners the Arkwrights, from a magnificent cascade just a few hundred metres from the new garden.

Water is an important theme in the garden, which sits in the apex of two rivers - the Lugg and the Humber. There is a long, formal canal between the walled garden and the house and an informal lake on one side of the drive.

A large cascade has been restored beside the path down into the Victorian sunken garden. This is hidden from the rest of the garden by a planting of Portuguese laurel, while a larger cascade falls six meters or more straight down a rock formation constructed by Waghorn and Colin Reynolds a digger driver.

"Bringing in water garden professionals would have cost hundreds of thousands of pounds so I have consulted the experts as we have gone along," says Waghorn, who admits that he was feeling extremely nervous when his water distributor was first turned on.

Beside this dramatic waterfall, a thatched rustic hermitage tucked into a cave disguises a curving tunnel leading from a tower at the centre of the maze.

The tunnel was another of Waghorn's brainwaves - not bad for a man whose previous experience consisted only of constructing a water feature for his family's own two-acre plot near Tring, in Hertfordshire.