Here’s a question: if you were wealthy enough to be able to buy a large plot of land in the country that came with planning permission to build a house, what would you do? You might hate the design of the house you were landed with.

To scrap it and design again from scratch, however, would take many months, and lots of money for everyone’s fees - £50,000-£75,000 for the architect alone on a large house that costs £1m or so to build, and more for a big name. So, would you grit your teeth and make yourself build something like this: Flow House, as it’s called, in deepest rural Kent?

Situated outside Bearsted - and near the village of Leeds, with its perfect moated castle - it is a rare example of a design that won planning permission on the basis of high architectural quality, which just goes to show that there’s no accounting for taste. Normally, you’re not allowed to build on agricultural land where no buildings already exist.

Planning law allows for excellence in a handful of cases, and that’s how this one happened.

What a strange beast the planning system is. I wouldn’t buy that if I had the cash - offers over £1.85m - in my back pocket. Especially given that you will probably have to shell out as much again tobuild the thing. On the other hand, it comes with 77 acres of woodland, fields and orchards: not quite an old-fashioned country estate, but for a single house, that’s a lot of land for your lolly. And it’s handy for London and Dover.

It’s unusual, for sure. MKA Architects, based in Tonbridge, have created a fantasia on oast houses and timber-boarded farmsteads in the form of an assemblage of three linked buildings. Unfortunately, it looks less like a modern interpretation of a farmyard than the lair of a lesser Bond villain. Bedrooms are in the form of individual pods, and there’s a separate office part that to my mind resembles an upturned boat rather than an oast house. There’s no great sophistication here (it’s a pale imitation of upscale American or Australian houses), but you do get lots of space: more than 12,000 sq ft, with five bedrooms, indoor and outdoor pools, stabling, a two-bedroom servants’ wing and so on.

The point is, this is a highly individual design, bespoke to the ultimate degree. Deborah and John Hebel, who own the land and commissioned the plans, want to be nearer their children’s schools in Canterbury. So, having obtained planning permission, the couple, who live in a temporary home on the site, described as “a grand shed”, have put their acres, and the design, up for sale. Who, I wonder, is going to buy into their vision?

Andrew Harwood, managing partner of the Tunbridge Wells office of Knight Frank, which is selling Flow House, says it takes time to match a buyer with such a piece of architecture - or, indeed, with a similarly dramatic project on nine acres in Grafty Green, a mere six miles away, that the agency is selling for £975,000. That scheme, designed by Future Systems, famous for the Selfridges store in Birmingham, has attracted plenty of interest, he says. “But you have to weed out the serial brochure collectors from those with a serious interest in that kind of house, and we have lots of both.” Again, it was the owners who commissioned the design, and got planning permission, before deciding not to proceed themselves. Whether the eventual buyer will build the house according to the same plans remains to be seen. Much of the attraction is the fact that it has planning permission at all. “It’s a truism, but they’re not building any more land,” Harwood says. “As the country becomes more overpopulated, plots of an acre or more become ever scarcer and more desirable.”

Some of these projects do sell, sometimes for huge prices. Take Orchid House, on the Lower Mill Estate, an enclave of affluent second homes in the Cotswolds. A curious organic design by the architect Sarah Featherstone, it was bought last month for £7.2m – avast amount for a property not much bigger than the average semi. The buyer, said to work in the entertainment industry, has not been named, but, having paid that much, will presumably go ahead with the design. Then again, he (or she) may want another architect to personalise it.

Houses, especially this kind, are very personal places. When they are built, it is often by the person who had the idea in the first place. One example is the ultra-futuristic home of Lady Helen Hamlyn: Holmewood, near Marlow, in the Chilterns. A crescent-shaped four-bedroom home, sunk into the landscape, it looks tremendous - far more stylish than the inevitable “Teletubbies” comparisons suggest. Planned with her late husband, the publisher and philanthropist Paul Hamlyn, it was completed after his death. Such a deeply personal project, you feel, would not transfer easily to anyone else.

When a house exists only on paper, however, big changes can be, and are, made. Two years ago, I went to see the site of an extraordinary house planned near Lustleigh, on the edge of Dartmoor. The architect Andrew Wright had come up with a highly ambitious curving-roofed house, stepping down the side of a valley, for his clients - who then decided their lives had changed and they didn’t want to build it. What happened to the design, which had been put up for sale, I wondered.

It seems the site finally sold just before last Christmas, after being on and off the market a few times. Julian Powell Tuck, the new owner, is himself a successful London-based architect. With a family of six, he needed a redesign, which has just been submitted for approval. “People used to think they needed these big-statement, landmark buildings,” sighs Powell Tuck, who has done up the old bungalow on the site in the meantime, and is in no hurry. “We’re just going to build a modest, nicely detailed stone box, tucked into the hillside.”

Sanity, perhaps, is returning to the market. A nice stone box on the Dartmoor fringes? I’d rather have that than Dr Evil’s overwrought Kentish lair, any day.

Flow House and Grafty Green are for sale through Knight Frank; 01732 744477, www.knightfrank.com

Breaking new ground

Obtaining planning permission to build a house on a site in the country where there hasn’t been one before is virtually impossible. Under Planning Policy Statement 7, which came into force in 2004, the go-ahead can be given for one-off country houses if they are “truly outstanding and ground-breaking”, and reflect “the highest standards in contemporary architecture”. Projects such as Flow House have been allowed under this rule.

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