This volatile, heart-on-sleeve Uruguayan-born architect has uncharacteristically quietly been running this low-key London office for a few years now but he's in town to press the flesh, give a lecture, and catch up with his two UK projects. To whit, the new Leicester Haymarket Theatre, which starts building next year, and the equally all-new First Site contemporary art gallery in Colchester, for which the design (a remarkable crescent-shaped building, designed to float, boat-like, on a key archaeological site) is now being finalized. He will present it to the planners in the New Year. Both are projects he won in international competition but by his standards they are tiny. £35m and £16m respectively, and an awful lot of faffing around to get to this point? It's not the American way.

Viñoly is the man for the big, often unexpected architectural gesture. Such as at his new $128m base for New York's "Jazz at Lincoln Center". This is no longer at Lincoln Center, but in the gargantuan new Time Warner complex at the south-western corner of Central Park, a sterile attempt at a Rockefeller Center of the 21st century. Typically, he fought for and got one big idea through the system. Jazz is associated with dark, smoky basements. But its new home is six floors up in a vast building, coincidentally designed by Libeskind's nemesis at Ground Zero, David Childs of S.O.M - the corporate architect preferred by the site's owner, Larry Silverstein, and who took over the design of Libeskind's "Freedom Tower". Jazz at Lincoln Center has several auditoria, recording studios, the works. It could all have been invisible. But Viñoly decided to open it up to the world.

A huge glass wall - 50 feet by 90 feet - behind the performers in the Allen Room auditorium opens up to Central Park and the lights of Manhattan. The audience gets the view out, while if you're outside, you can see what's happening within, rehearsals and all. Needless to say he had to fight like a wildcat to achieve this goal - and to get the necessary transparency - but there it is: Jazz at Lincoln Center has become a very public institution, and by general agreement is the only good part of this deeply banal set of commercial buildings.

Viñoly is undoubtedly now part of America's architectural establishment. He refuses to bad-mouth David Childs, wisely enough in view of Libeskind's losing battle with him ("We didn't have the same experience as Daniel at all."). But simultaneously he is himself an outsider. He is the little silver-haired, multi-lingual South American with the heavy accent, head festooned with an assortment of spectacles on strings, who had a successful firm in Argentina before the political situation got too heavy and he upped sticks and started afresh in the States. He made his name the second time with the ingenious mid-1990s Tokyo International Forum - a high-concept arrangement of concert and convention hall with covered public space. So when I ask him why he now bothers with Britain, he replies that, in a way, it's a repeat prescription.

"It's the same type of situation - but actually far more promising - as when I started in New York. You have to go through the motions of demonstrating that you have something to offer. That's why these two projects - Colchester and the Leicester Haymarket - are so important for us. They are projects that can be done with a much more specific attention to the way buildings work."

By which he means? "Well, there's the sympathy we have for the way British architecture interprets structure - the logic, the thinking. We're not corporate, more artistic. So to do this kind of work in Britain is sort of the ideal condition for us. But we also come with what we've learned from years of practice in New York - efficiency, programme-making, dealing with all the constraints."

So Viñoly is impatient to get going in Britain, feeding his London office with projects elsewhere in Europe. Meanwhile, he's enjoying the English shires - Essex and Leicester. "The great thing is that, unlike America, provincialism doesn't equate to lack of culture here. These people are extraordinarily cultured," he enthuses. "The Leicester Haymarket, for instance, is far ahead of any other theatre company I know, with their understanding of theatre in the community as an economic force." As with Jazz at Lincoln Center, he is opening up the theatre to the street, bringing transparency to a traditionally hermetic activity.

So here's the pitch: Viñoly, regarded as a touch radical in the States, reckons he can fit in nicely over here and do things faster than we're used to. However, he's come up against one particular British disease - talking rather than doing. He is indulgent about this, but plainly slightly baffled.

"I'm totally amazed by the amount of talking," he says. "There must be some very important enabling mechanism for people to be so discursive about things. As for me, I wonder how you afford so much talking." He pauses. "Obviously you can afford it. Because people talk. The process becomes endless. You need an enormous amount of political support but the only person that can lead this kind of process is" - and he drops his voice for dramatic effect - "an architect."

And I think we know which architect he has in mind. He's right, though: in the world of British cultural buildings, too often we'd rather talk a project to a standstill than see it happen. As we witter on, costs inexorably rise and enthusiasm steadily wanes. Why do we do this to ourselves? I hope Viñoly finds out. He could do us all a service. Or he might just get fed up and go home.

www.rvapc.com - website of Rafael Viñoly architects.