First Night: AbbaWorld, Earls Court, London

ABBAWorld opened last night in a flurry of spangled jumpsuits and cacophonous harmonies. The basement of Earls Court's cavernous exhibition centre was transformed into a 25-room shrine to everything that was bouncy, shiny and optimistic in the 1970s, when a Swedish quartet called Abba won the Eurovision Song Contest with a song about Waterloo and went on, Napoleonically, to conquer the world. The exhibition, curated by Touring Exhibitions, features interactive holograms, karaoke booths, gold discs and video installations. It's open to the public from today, and will go on to tour across Europe.

The evening kicked off with champagne in the Brompton Room, temporarily transformed by black drapes and twinkling lights into a kind of cosmic cocktail bar. Large shouty European entertainment moguls with shaven heads greeted each other with theatrical slaps. Boy George, in an outsize yellow hat, talked earnestly to a chap with his hair arrayed in Satanically crimson horns.

In the crowd, a long way from their native Brisbane, were Jacinta Wagner, a clinical psychologist (and a dead ringer for Agnetha Faltskog) and her husband Mike, a Qantas airline pilot, who had bid €1,200 in a charity auction to win a ticket to tonight's event. Jacinta has a huge fan for years. "There's no more outstanding musical compositions than Abba songs," she breathed. "They completely changed pop culture." Had she ever seen them live? "Her parents were too poor to take her to see them," said her husband, "so she's making up for it now."

After perhaps too many speeches of thanks, and affirmations that "Abba are literally responsible for the musical landscape in which we all live", two of the original line-up appeared on stage – Bjorn Ulvaeus and Anni-Frid Lyngstad. The crowd went wild. Anni-Frid is blonde these days but just as coolly distant as in her prime. "We hope you like the interactions," she said. "Me and Bjorn sang two of our songs downstairs. It wasn't quite like before, but it was okay." Bjorn, looking professorial and serious in spectacles and beard, reminded the crowd that the quartet had shifted some serious product in its time. "Can you imagine 375m CDs? I can't." Of the exhibition, he remarked: "We feel like pioneers again, like we did when we did 'Mamma Mia' [on stage]."

The crowd dispersed at impressive speed to try the machines in the basement. In a karaoke booths, two German business types in grey Baldassarini suits and artfully slicked long hair, sang "Fernando" with their arms round each other like survivors of a revolution. In the dancing area, where screens full of colour-coded arrows direct your steps as you try to master "Dancing Queen", the highest score went to a lissom, high-strutting young woman called Ruth Matthews who had come with her best friend, Heather Mills. The former Lady McCartney had a little strut herself, fresh from her triumph in Dancing On Ice.

The exhibition's astonishing centrepiece is a "high-definition holographic video system" which gives exhibitionists a chance to perform onstage beside four illusory Abba figures.

As we milled through rooms that offered footage of the Swedish quartet's pre-Abba days (when Bjorn was with the Hootenanny Singers and Benny with the Hep Cats,) unlikely Abba fans materialised. "We were guests on the Abba TV show once, and it was a big thrill for us," said Phil Manzanera, ex-guitarist with Roxy Music. "And of course I like the songs. A few of them contain some of the best riffs in the world. And all of them provide a lot of happiness for a lot of people."

Outside, I asked Boy George for his favourite bit of the show. "Definitely the costumes. I was a punk when they were around, so I hated them, but I love them now, especially the clothes. I wish the whole exhibition had been clothes."