It turns out that he has not yet sat down with Livingstone to discuss the GLA building (his client is not Ken, but the Government Office for London), though they've met at a party. "That's just a matter of time. I think our agendas overlap very closely. I would have thought that the way we address the issues of public transport, the quality of urban life, green architecture, projects like Wembley - these are very, very close to his agenda."

The Zeppelin in the City is proving more problematic, and Foster gets quite heated about it. For him, it is a very refined building, a new type of tower. "It's not whimsy. It's rooted in an incredible intellectual rigour, planning rigour, structural rigour, environmental rigour, with a continuous spiral of a garden to act as a lung. It takes that quest for a better working environment one notch further." Moreover, his client doesn't want any car parking, has bought the public transport message. "These people should be given bribes to come to London, instead of having life made difficult for them."

A constant Foster refrain is how long it takes to get anything built in this country compared to anywhere else. He built the world's largest airport in Hong Kong at incredible speed, while his old chum Lord Rogers is still mired in the Jarndycean nightmare of the £100m public inquiry for Terminal Five at Heathrow. "You could have built the bloody airport for the cost of the public inquiry," he observes.

But he usually overcomes the hurdles in Britain. Even in the dark days of Prince Charles, his architecture was deemed acceptable. Foster defines his style as "A lightness of touch, the creation of more egalitarian spaces, of breaking down barriers. I think that quest still continues." So it does. When I ask him what project he would most like to tackle next, he goes into stream-of-consciousness mode. He wants to plan some type of community, where people would live and work and play, with noble public spaces, maybe one which he would instigate himself rather than merely respond to as an architect. "If you can get closer to the heart of the process, arguably one could be more effective," he says gnomically. Right then. Some kind of 21st century Utopian garden city? "It could be. It's not a desire to operate on a grander scale. It could be relatively small. It could be in a city or it could be, as you say, more removed. But those are the ingredients."

Stretching the boundaries, he observes, is an extraordinarily time-consuming and draining activity. Prophetic words. Soon after that conversation, his bridge began its famous wobble. And Foster turned out to be human after all.