You can criticise some aspects of the Gherkin's architecture - for me it is a bit clumsy round the base, where the entrance has been carved rather crudely out of the beefy steel latticework structure. Inside, its spiralling atriums - arranged in stacks of six or two, depending on the office configuration - are smaller than originally planned and not as dramatic as you'd hope, though they do bring light and fresh air right into the interior and open up more views out. But these are quibbles. As a London landmark it is simply very good. Placed close to the historic centre of the City, essentially on a medieval crossroads, it acts as a lynchpin to the skyline. You can see it from every direction and, being circular, it has no bad side. It cannot turn its back on anyone. It looks as if it has naturally grown there. Its jazzy, almost Deco, two-tone external patterning with its subtly shifting geometries is confidently handled.

In short, this has restored the blue-chip Foster reputation: a reputation that had suffered around the time of his famous wobbly (now firmly fixed) pedestrian "Millennium Bridge" linking St. Paul's Cathedral and Tate Modern. Foster's busy office has also suffered recently from the defection of his high-profile right-hand man, Ken Shuttleworth (instrumental in designing the Gherkin) and several other staff. But Foster somehow always emerges stronger from such events. He is involved in everything from the new Wembley Stadium in London to Beijing's mighty new airport. At 68, lean and fit, with his young Spanish wife Elena and several children, perched in their eighth-floor Foster-designed penthouse in Battersea, his interests now are as much environmental as architectural. For instance: how do you build all those new homes without destroying the countryside?

"If you expand London out into precious green space, there has to be a very strong emphasis on transport infrastructure, on how people move. That has to be in early, not following along afterwards like the Docklands Light Railway." he says. "And whether you build low, medium or high - or a mixture of those things - it has to recognize the importance of density and a balance of green space."