"It's a glass box, really," says Adam, who is probably trying to wind me up - come on, Bob, there's still a lot of stone in there. "This is recognising that the classical tradition has to progress, so it takes up where Thomson or Richardson left off."

In a more 18th century tradition, this is not just a house but a house in a landscape, complete with lawns, formal gardens close to the house, a long vista across arable meadows to lakes in the distance, and the odd pavilion dotted about. But the landscape, by Barton Willmore Environmental, is not made in the way it would have been in planner-free Georgian times. "What has changed is that whereas in those days landowners would shift the land around, make hills, move woods and so on, today you not even allowed to uproot a hedgerow there. So you have to find the geometry within the land itself," says Adam. Consequently the house is made to fit the landscape, rather than vice-versa. This means it faces north-west, so the main lawn and formal gardens are placed behind it to catch the southern sun.

Now in his early fifties, Adam has a shock of unruly hair of the kind that, unattended, tends to stick up vertically. He can get noisy, even belligerent, when he senses he is being patronised by the modernists or misunderstood by planners. He does not toady to royalty. He is good company. And - this is where he becomes more difficult for the modernist establishment to pigeonhole - he is not a classical fundamentalist. He is light on his feet, sees innovation as the way forward for the style, prefers not to live in a supposed golden age of 18th century English Palladianism.

I have seen a house of his which has slender steel columns, abstract, stainless-steel quasi-Corinthian capitals, and glass balustrades. His Sackler Library next to the Ashmolean Museum in Oxford, opening later this year, is an exercise in circular geometry reminiscent of the Swedish early-modern master, Erik Gunnar Asplund. In scholarly fashion, Adam gives the library a cylindrical gatehouse based on the Temple of Apollo at Bassae - a building originally excavated by C.R. Cockerell, architect of the Ashmolean. But in the past he has also designed - just for the fun of it, with no hope of ever seeing them built - classical high-rise housing blocks, linked by high-level bridges, to be dropped into the urban wasteland of Spaghetti Junction in Birmingham. As he points out, classicism readily adapted itself to the dawn of the skyscraper age in America, so why not here? The influences are plain to see, and Adam is as prepared to borrow from modernism as he is from the ancients.

He is very self-aware, and knows that the modernist establishment likes and tolerates him, but does not subscribe to or even understand his views. Classicism is still a fringe movement, building mostly - as in Hampshire - for the moneyed country set. In a lecture he is due to give in America next week, Adam argues that classical architecture is at present defined and therefore shackled by the modernists, and that it needs to break free of this yoke.

With so many classicists content to live in the past - in other words, on a reservation pegged out for them by the modernists - this is a brave stance to adopt. But Adam knows what will happen if innovation is stifled in his chosen style. "New classicists have painted themselves into a corner, and classicism now carries with it the seeds of its own destruction. There seems only the option of doing the same thing, without progress, a way forward and a future." But in the past, he points out, classicism went through many phases of being new and shocking, and always embraced new technology as it did so.

Adam wants to revive that progressive, radical attitude. So it is paradoxical that he is growing wealthy principally on commissions from conservative clients who are only too happy to live in the past. He needs a new kind of client to achieve his 21st century vision. He needs to build commercial office blocks, shopping centres, airports. It sounds highly unlikely, but you never know: if anyone can make it happen, Adam will. And if he does, chances are he does it in America.

Link to Robert Adam website: www.robertadamarchitects.com