Despite the weather, a garden-fete atmosphere reigned inside the fenced compounds rigged up at both ends of the bridge. There were even raffle prizes on offer. Architects and engineers’ offices all over London had been emptied to make up the numbers. There were 130 from Foster’s office alone, including a clutch of his senior partners. There were hundreds more from Arup, an international engineering consultancy, including its chairman, Bob Emerson. The bridge’s original engineer, Tony Fitzpatrick, had flown over from the States wearing a rakish beret and was happily taking photos. There were thesps from the nearby Globe Theatre, culture vultures from Tate Modern, teachers from the City of London Boys’ school on the North bank, even a few okay-yah types from City dealing offices. Sculptor Sir Anthony Caro, who had worked with Foster on the initial bridge design, was there. And me, wishing I’d worn a thicker coat. But no Lord Foster. Perhaps he couldn’t bear the suspense - or the ignominy, if it all went pear-shaped again.

Tannoy announcements barked. “You’re here to enjoy yourselves,” crackled a voice, urging us to feast our eyes upon the eternal beauty of floodlit dome of St. Paul’s cathedral. Then the voice warned us to step aside if we felt ill on the bridge. The implication was that if we didn’t we’d be trampled. Just slightly nervous now, we all lined up. Marshalls with flags got ready. A small orange lifeboat moved into position beneath the bridge. St. John’s ambulances were standing by. This was an exercise arranged with extreme caution and military precision. And then the marching began. Up the ramps we went. We walked briskly across one way. We turned around, and walked briskly back the other way. Then we undertook a slow shuffle. Which was interesting, because when walking very slowly in a crowd, people showed signs of starting to sway from side to side in unison, which was what got the bridge swinging wildly in the first place.

But this time, the bridge scarcely moved. Apart from a slight springiness on the southern ramps next to Tate Modern, which are now stabilized by pairs of giant tubular shock-absorbers, it seemed as steady as a rock. Electronic sensors placed along the bridge were ready to record any untoward motion. Wind speed - there was quite a breeze - was being measured. Video cameras were trained on us as we walked. And some old-fashioned methods were used. A chap with a Stanley tape-measure checked the up-and-down movement at the southern end.

And that was that. The Tannoy voices declared themselves satisfied. Having spent the evening patiently queuing and shuffling, we were all promised a nice cup of tea inside Tate Modern. Everybody started patiently queuing and shuffling all over again, as industrial quantities of tea were dispensed inside the cathedral of modern art. The engineers were smiling. “Uneventful,” said one. “that’s the way I like it.”