The level of craftsmanship, compared to British construction sites, is high. Just as well, says Martin Wood. "It's the sort of design that needs to be well built. The spine had to be a very well-made item. We're pleased with it." Indeed, this is the kind of ambitious scheme which you can just imagine British workmen bodging up horribly, particularly at key points, such as where glass panels are carefully laid in around the double-curved form of the spine. Not that everyone appreciated it. The Spine marches down the house on red-painted angled steel legs, straddling a hallway-cum-art gallery below. Some visitors ask what the final colour is going to be. Others ask when the props are going to be removed. The house has taken so long, it's obviously hard for some of them to believe it's finished.

A clear hierarchy of spaces moves you from the entrance (which is really at the back) through to the big events of the garden façade. The rear of the house contains garages, utility rooms and, slightly startlingly, a large internal squash court on one side, and swimming pool on the other. The living areas are in the front half looking out over the landscape - bedrooms, studies for both Blases, the sitting-around bit, the kitchen and dining zones. In the summer, this is where they live. In the winter, says Frank, they retreat up into the warm interior of the Spine which he describes (yet another organic metaphor) as a womb. After all, you can read that oval rocket-nozzle front door as a different kind of orifice. The ambiguity is part of the game. What's male, what's female, in this house for a married couple?

Where do you place the Spine House in the modern house tradition? Functionally, it works just as it was intended to. The Blases now come home, they say, in a way they just didn't used to. They get fit, they relax, they entertain. It also suits the progressive image of their company. In architectural history terms, it has a further significance. Take an iconic post-war modern house plan, slice it open, shuffle it around, introduce an alien element. Set the right angle against the curve, the mechanical against the organic, the hard against the soft. After all this time waiting to do a one-off house, Grimshaw, the arch-modernist and technophile, has composed a powerful critique both of orthodox modernism and the technological obsession. He has rethought the house from scratch, and made it a richly symbolic, almost pagan, object. It has its awkward moments. But it is a strange and rather wonderful place to be.