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Will the winners take it all one more time?

A reunion? Don't talk to Abba about a reunion. Except, of course, that it's hard not to. Benny Andersson and Bjorn Ulvaeus are aware of the protocol.

"Don't worry, I know you have to ask," says Andersson, a baby-faced 64, when he sees me edging towards the question. The last time I edged uneasily towards the question, in May 2002, Ulvaeus said flatly: "There's no amount of money in the world that could persuade me to do that."

Since then they've regularly been politely rebutting requests to re-form , not only from fans who weren't born when Abba imploded, but from promoters who, according to Ulvaeus, offered "crazy" sums for a farewell tour -- in one case $1bn (f700m). Every time the thought of "the looks on the faces in the audience as they realised we had grown old" meant that Abba had long faced their Waterloo.

Eight years later, there's no reason to believe that Ulvaeus and his songwriting foil of four decades might react any differently. And yet, for one extraordinary moment at the end of our encounter, a realisation stirs into life that there may be a way to turn the longed-for reunion into a reality.

Andersson and Ulvaeus are in London overseeing rehearsals for the UK premiere of their most ambitious project. Abba fans might want to take a raincheck on Kristina when it comes to the Albert Hall next month.

On the face of it, Vilhelm Moberg's 2,000-page epic about Swedish emigrants in the 19th century isn't the most obvious of contenders for musical theatre treatment. Nevertheless, in 1995, when Kristina opened in Malmo, Swedish reviewers greeted it with a fervour that eclipsed anything that Andersson and Ulvaeus had achieved with Abba. Quite what audiences will make of it is another matter. "We've cut the play down from three hours to two," Ulvaeus says. "And I approached Herbert Kretzmer, who did Les Miserables, to translate the lyrics into English."

Be that as it may, newly retitled highlights such as Burial At Sea, I Am Reconciled to My Fate and Miscarriage confirm that Mamma Mia 2 is very much not on the cards. To Andersson it's a chance to show a British audience what he and Ulvaeus have been up to. "One reason we never cared about breaking America," he says, "is that the English people treated us like their own." Ulvaeus adds, though, that "it did make us spoilt. With Top of the Pops you could reach all of Britain. But in America you reached a tiny audience doing silly TV shows we didn't want to do anyway."

I suggest that some members of the group showed their reluctance a little more readily than others. Anyone who persists in believing that blondes have more fun might care to read Agnetha Faltskog's 1997 autobiography As I Am. "No one who has experienced facing a screaming, boiling, hysterical crowd," she wrote, "could avoid feeling shivers up and down their spine. It's a thin line between ecstatic celebration and menace."

Was it really that bad? As her ex-husband and father to her two children, you'd think Ulvaeus would know, but he sounds unsure. "She didn't seem unhappy at the time. It's strange the way that history sometimes becomes rewritten and it becomes the truth."

He's not just talking about Faltskog here. Such revisionism, he feels, also extends to the place Abba hold in the collective memory. "It's not just people wanting to hear the songs. It has more to do with people wanting to be in some kind of mood that is fictitious. A mood of 'the Seventies' that Abba represents but is not rooted in reality. For instance, we never thought in our wildest dreams that we would be gay icons."

At times, Ulvaeus's perspective on Abba's legacy is so unknowing that it's a struggle not to leap across the coffee table and hug him. How could he and Andersson have written Hi-NRG hymns to physical desire such as Gimme Gimme Gimme (A Man After Midnight) and Lay All Your Love on Me and not think it might play out well with their gay fanbase? "We didn't realise it. We were just releasing another song, that's all."

Play Abba's albums in chronological order and the effect is something akin to having your emotional dimmer switch turned slowly down. With the bulk of 1980's Super Trouper album written after Ulvaeus and Faltskog's divorce, the group's music changed to mirror their personal situations. The Winner Takes it All was written in a red wine-abetted stupor of self-pity. "Usually it's not a good idea to write when you're drunk," Ulvaeus says, "but it all came out on that one."

By the time they recorded their last song together, The Day Before You Came, "we were really in the dark", Andersson says.

For the remainder of the 1980s, Ulvaeus felt that "our music had fallen so out [of fashion] that people looked down on it". In the early 1990s, when tribute bands such as Bjorn Again popped up, they merely compounded the uneasy feeling in Ulvaeus's mind that people were laughing at Abba. "But then I spoke to people who went to the shows. They said that it's a happy feeling and that people are enjoying themselves immensely."

Years later, of course, we know that irony is merely the first step on the way to critical and commercial rehabilitation. It isn't irony that has sold 28 million copies of Abba Gold.

In London, such is the love for Abba that thousands of fans a week are paying £21 each to see the Abba World exhibition that includes karaoke opportunities and replica Arrival helicopter "It was a chance to clear out some stuff from the attic," Andersson says. "Have I been to see it? No. I lived it the first time."

No point then in asking if he would want to live it again. Probably not. But footage of Faltskog at Abba World, talking with surprising affection about her contribution to the group's biggest hits, is fresh in my mind.

Reunions can take all sorts of different forms. A lucrative world tour might be out of the question, but what about something more low-key? I float the idea of an intimate, one-off performance for invited guests and families, perhaps with a small orchestra. The whole thing could be filmed and the rights licensed out to TV stations around the world.

Alluding to Super Trouper's final song The Way Old Friends Do, Ulvaeus's first response is seemingly in jest: "We could sing The Way Old Folks Do!" Andersson, by contrast, seems deeper in thought. "Yeah, why not?" he nods. As if working through the logistics, he adds: "I don't know if the girls sing anything any more. I know Frida [Anni-Frid Lyngstad] was [recently] in the studio."

And on her most recent solo album, five years ago, Faltskog was in fine voice. "If you can sing, you can sing," he concurs. Then, a little later, "It's not a bad idea, actually."

Alas, though, as the door to a reunion appears to open ever so slightly, so does another one. Andersson and Ulvaeus have to rush back to the Albert Hall, where rehearsals are under way. In two weeks, Kristina has its premiere. And then what? Like the song goes: "If you change your mind . . ."