The Eagles have landed in London

The Californian rockers are in London this week for the UK premiere of a new film that tells the extraordinary inside story of the supergroup. You couldn't make it up, says David Sinclair

The manager of the Eagles, Irving Azoff, has a small plaque on the wall of his office mounted next to a disc of Their Greatest Hits (1971-1975). The inscription says: presented to the Eagles to commemorate the best-selling album of the 20th Century [in America] with sales in excess of 26 million units. "That century's gone, so nobody's going to top that," Azoff proclaims with a satisfied air of finality towards the end of History of the Eagles, a new documentary telling the inside story of the group.

While plans are being finalised for an American tour beginning on 6 July, Glenn Frey, Don Henley, Timothy B Schmit and Joe Walsh will be in London to submit to a Q&A session on Thursday following the first British screening of History of the Eagles at the Sundance Film and Music Festival.

These four men are the remaining members of a band which has weathered many bruising internal conflicts and external changes to the musical landscape while somehow maintaining a level of mainstream popular appeal that has hardly dipped since their heyday in the 1970s. Even when they stopped working together for 14 years from 1980 to 1994, their music never dropped off playlists, particularly in America, where the group's temporary demise coincided with the arrival of classic-rock radio – a format more or less defined by the musical legacy of the Eagles.

How have they done it? Why are people, all over the world, still fascinated to know what went on 40 years ago among a group of musicians in southern California? "We set out to become a band of our time, but sometimes, if you do a good enough job, you become a band for all time," is how Henley explains it, somewhat immodestly. "Perfection was not an accident. Our goal was to be the best that we could be."

The Eagles emerged from Los Angeles at a time of incredible artistic creativity. A network of troubadours (Jackson Browne, Joni Mitchell, Gram Parsons) and harmony groups (the Byrds, Crosby Stills & Nash, the Mamas and Papas) were in the process of turning California into the centre of the pop world. Frey and Henley, together with the original bass player Randy Meisner and guitarist Bernie Leadon, began their professional association as members of Linda Ronstadt's backing band before the four of them broke away to form the Eagles in 1971. Signed immediately to David Geffen's label Asylum, they enjoyed success with their first two albums, Eagles (1972) and Desperado (1973), which painted an improbably glamorous picture of a laid-back lifestyle interwoven with a rock-star homage to the mythology of the old Wild West.

"Before cheap air travel and all that, the west coast of California was still some kind of Xanadu, only seen in cool movies such as Bullitt and The Long Goodbye," says Nick Stewart, a management consultant for the Eagles in London. "Original fans like me heard those records and fell in love with the whole cool American sound and image of the band."

New generations of fans may be surprised to discover that both those albums, with their iconic American sound and artwork, were recorded in London with the English producer Glyn Johns. When he first heard the group, Johns was not convinced. "I didn't see what all the fuss was about," he says. It was only when he heard them singing a cappella harmonies that the penny dropped. "An extraordinary blend of voices, a lovely harmony sound; that was it," he says.

Allied to this vocal talent was the instrumental brilliance of the group's several guitarists. Frey and Leadon were joined by Don Felder on the albums On the Border (1974) and One of These Nights (1975) and Leadon was then replaced by Joe Walsh, formerly of the James Gang and already a fully qualified guitar hero in his own right.

The final piece of the artistic jigsaw that made the Eagles such a massive global success was their borderline-obsessive attention to the craft of songwriting and recording. "They never made a poor album," Stewart says. "Like the Beatles, their standards were, and still are, unbelievably high." Nowadays, when the Eagles do a 31-song concert, the audience know the lyrics to every song. And most people can probably even hum the guitar solos note for note.

"People told me they didn't just listen to the Eagles," Frey says. "They did things to the Eagles. They went to a fandango and drove across the country with their high school buddies. People broke up with their girlfriends, quit their jobs or changed their lives; they did things to [the music of] the Eagles."

The scale of the group's success is staggering. People often overlook the fact that their biggest non-compilation album Hotel California was released after Their Greatest Hits. Some of the group's most successful songs – "Life in the Fast Lane", "New Kid in Town" and "Hotel California" itself – are thus not even included on the best-selling disc of the 20th century that proudly sits on Azoff's wall.

As the group became megastars, a familiar tale of lifestyle excesses ensued. Copious quantities of liquor and cocaine were consumed at their notorious "third encores" (after-show parties). Walsh, who became the self-appointed "master of room trash", ended up an alcoholic. But it was the constant struggle to maintain such high artistic standards which produced a succession of epic personality clashes between various members of the band over the years, usually involving Frey.

Leadon owns up to pouring a bottle of beer over Frey's head in one dressing room fracas. "I wasn't proud of myself," he says. And there is an extraordinary recording of an onstage bust-up at a gig in Long Island in 1980 during which Frey and Felder squared up to one another in a string of increasingly aggressive exchanges captured for posterity in a "Troggs Tapes" moment. "Three more songs, asshole, and then I'm gonna kill you," Frey says. "I can't wait," Felder replies.

"In my experience, all rock'n'roll bands are on the verge of splitting up at all times," says Schmit, who took over on bass from Meisner for the aptly-named album The Long Run (1978), soon after which the band stopped. Henley's often repeated assertion that they would get back together again "when hell freezes over" provided the title for the reunion tour of 1994 and an ensuing live album. Now, nearly 20 years into their second act, the Eagles show no signs of slowing up; quite the reverse. Unusually for supergroups of their vintage, all seven members, past and present, are still alive. And as their Californian contemporary Jackson Browne succinctly observes: "The songs last."

'History of The Eagles' premieres at the Sundance Festival, The O2, London, Thursday at 9pm, followed by Q&A session with the Eagles (www.sundance-london.com). The film is released on DVD and Blu-ray on 29 April

Hotel California: What is the Eagles' most famous song about?

"The song has taken on a mythology of its own, like the Paul is dead thing or who was the Walrus," says Don Henley, referring to myths that grew up around the Beatles. "It's been denounced by evangelists. We've been accused of being members of the Church of Satan. People see images on the album cover which aren't there. Just lunatic stuff. The hotel itself could be taken as a metaphor not only for the myth-making of southern California but also the myth-making that is the American dream; because it's a fine line between the American dream and the American nightmare. It's a song about a journey from innocence to experience. That's all."

Glenn Frey says: "'Hotel California' was our reaction to what was happening to us. It became a theme for the album. Don and I are fans of hidden, deeper meanings. Maybe somewhere in that song there's some stuff that is just yours; that no one else is ever going to figure out."