So Grimshaw and Whalley produced a £106m design, which wrapped a glittering Waterloo-type glasshouse around the sides of the old pit. And the Millennium Commission rejected it, outright. Smit decided to pretend that this setback had not happened, Grimshaw and Whalley refined their designs, tried again, with the same result. Finally they produced a smaller scheme (originally they had planned a third, desert-climate “biome” as well) and resubmitted it. Crucially, they also adopted an entirely different, lightweight construction technique: the geodesic dome, as first popularised in the 1950s by a hero of Grimshaw, the American designer-inventor-ecologist Richard Buckminster Fuller. Instead of glass, Eden’s domes would be glazed with featherlight inflated pillows of a wonder-material known as ETFE foil. Translucent rather than transparent, ETFE lets through more light than glass does, insulates better, doesn’t shatter and - being so light - requires only a delicate structure to support it. Grimshaw had used it before, but never on such a scale.

All these changes brought the cost down to a theoretical £75m, later to rise a little again. At the same time, Smit decided to scale down his highly ambitious projected visitor numbers, forecasting a more reasonable 750,000 a year. The trimmed-down Eden Project passed the Millennium Commission’s somewhat arcane financial tests and made them feel good about having an all-new landmark project in economically-deprived Cornwall. They promised the scheme half its money - £37.5m.

It was just enough. With that as collateral, Smit could leverage money from the European Union, the English Partnerships regeneration agency, banks, builders, everyone. Fees could be paid, serious work could begin. But the finances were, as Smit happily admits, distinctly shaky right through to mid-2000, by which time construction was in full swing. It was still being run in a rock ‘n’ roll way. Eden’s domes could have imploded at any time. But Smit, like a surprising number of people from the music business, has a business brain lurking beneath the laid back exterior. He knew he needed sharp financial managers, and he brought them in. Possibly, just in time. Similarly, he brought in top botanical talent from Kew and elsewhere to provide scientific credibility. An amateur himself, he needed experts.

But by the time the Millennium Commission said yes, it was already 1997, and giant trucks were still extracting clay from the old Bodelva pit. Design work went into overdrive. The pit was 60 metres deep, with hardly any flat ground. Its sides were unstable. It had a tendency to spurt water spontaneously from fissures all over, and it had no usable soil, only clay waste. Even those who have worked on the project throughout, such as Smit’s media manager Paul Travers, a former habitue of the Abbey Road recording studios, admit wonder that the thing has arrived, as designed, in such a relatively short time, despite ghastly conditions in which, at one point during months of heavy rains and high winds, it seemed as if the whole site was going to slump into a morass. Grimshaw himself admits to wonder on visiting the place he designed, and finding it actually built. Because it has that Xanadu air of unreality hanging over it. Surely this can't exist? Not here? Not now?

But it does. They found a way to live with the elements. They sculpted and stabilised Bodelva Pit, emptying perimeter spoil tips back into the depths to create a flatter floor. They made their own soil, mixing china clay waste with organic material. They even made the back wall of Grimshaw's entrance building out of rammed earth from the pit, as a demonstration that high-tech does not have to mean high-cost or high-energy. And meantime, those hundreds of steel hexagons and thousands of connecting pieces and a multitude of ETFE pillows, each one like a huge air bed, were being made to precise, computer-calculated tolerances. When the pieces arrived on site, they fitted together like Meccano, supported on a dense forest of scaffolding. With the last piece in place, the scaffolding was knocked away and the bubbles finally floated free. It is estimated that they weigh no more than the air they enclose.