Bono worries U2 will be remembered as a "very good" band rather than a "great" one.

The 'Even Better Than The Real Thing' rockers are unveiling a new documentary, 'From The Sky Down', which focuses on their struggles to cope after poor reviews for their sixth album 'Rattle and Hum', and while they have gone on to become one of the biggest bands in the world, frontman Bono worries about their legacy.

He told "I found it a little humiliating to realise that we were so inept and these days we're a better band.

"We've learned our craft - and therein lies the huge danger, which is there's a giant chasm between the very good and the great, and U2 right now has a danger of surrendering to the very good."

However, after criticism for 'Rattle and Hum' led to infighting between the group - which also includes guitarist The Edge, drummer Larry Mullen Jr. and bassist Adam Clayton - director Davis Guggenheim claims their single 'One' "saved" the band.

Bono said: "Making 'Achtung Baby' is the reason we're here now."

Davis explained: "The movie has this pretty long section where you hear them write 'One' - and it's goose bumps.

"The writing of that song really saved the band. They had come out of the height of 'Joshua Tree' as the biggest band in the world. 'Rattle and Hum' was a disaster from their point of view, a lot of bad reviews - they weren't happy with what they had become.

"They Take That bridge section out of 'Mysterious Ways' and they go back into the room at Hansa. They write a song on The Fly in a matter of minutes. 'One' is written and the band is saved and we have all that on tape."