After the acrimonious break-up of The Eagles in 1980, Don Henley, co-founder of the rock band, famously quipped that they would play together again “when hell freezes over”.

All was harmony, though, at the Connaught Hotel in London on Thursday morning when Henley and fellow band members Glenn Frey, Joe Walsh and Timothy B Schmit met journalists. They were in town for the Sundance London screening of new Alex Gibney produced feature doc, History Of The Eagles Part One.

“We wanted somebody that was going to make a truly great film for us,” Frey explained why the band recruited the Oscar-winning documentary maker Gibney to tell their chequered story on screen. Gibney in turn brought in Alison Ellwood to direct the film.

“We wanted someone who had not done a lot of band documentaries,” Henley said of the choice of Gibney and Ellwood rather than filmmakers more closely linked with the music world.

The Eagles may have initiated the film but it offers an unvarnished, warts and all view of the Los Angeles band in its turbulent, feuding, drug-taking prime. Band members insisted they gave the doc makers a free hand to tell their story.

“We didn’t do a lot of ‘oh, you’ve got to take that out’ or ‘you need to re-do this, I have to say that,’” Frey said of the film which carries footage of himself and former band member Don Felder trading insults on stage at a benefit gig. (“Three more songs, asshole, and I’m gonna kill you.”)

In their heyday, from 1971 to 1980, the Eagles changed producers, band members, managers, agents and record companies. “There was always something standing in our way, challenging us to overcome and get beyond (it),” Frey said of the multiple challenges the band faced.

“I was surprised we had any time to write any songs at all,” Henley agreed of the period in which they recorded such songs as Desperado and Hotel California.

The doc includes some pointed criticisms of David Geffen who championed the band early on and signed them to his Asylum Records label but later became embroiled in contract disputes with the band.

“We started out knowing very little about the music business and we learned some lessons the hard way,” Henley acknowledged.

The Eagles are shortly to begin rehearsing for what may be their final world tour. This will start in the summer in the US and Canada and is expected to continue to Europe in 2014.

When they originally reformed in 1994 for their “Hell Freezes Over” Tour, guitarist Joe Walsh   recalled that he finally managed to overcome his alcoholism and drug addiction. “We can’t do it unless you’re sober,” Henley and Frey told him.

Henley, though, defended the band’s hedonism during the 70s. “At that time in history, everybody was behaving (that way) - doctors, lawyers, Wall St types, they were all doing it. It was that kind of time. The lesson to take away from this is that we all survived. We are all alive and well. We’ve been through the fire. A great many people didn’t make it both in the States and here in Britain…” Besides, as Frey put it in the doc, “90% of the time, being in the Eagles was a fucking blast.”

Following its international premiere at Sundance London, The History Of The Eagles is being released on DVD in the UK at the end of the month. Showtime bought the doc in Sundance in January and aired it in the US in February.