An unreleased song composed by U2 around 30 years ago is to be revealed in the new film Killing Bono.

The song, Secret Mission, was recorded by the band shortly after they formed but it has never been heard by the public before.

Despite being three decades old, the song is only coming to light now because of the film's music producer, Ciaran Gribbin, who was given the thumbs- up by the band to rework some of their earliest material for the actors to perform.

The Derry singer said he was brought in as a music supervisor and producer for the highly anticipated film and found it a "dream come true" to work with the raw song.

"Hopefully everyone will be really happy with it," he said.

"It's an absolute dream come true. I've been writing music for a long, long time - I did eight songs for the movie - but it remains to be seen how it came out in the end. I hope the public will get it. I'm confident with what I've got though.

"It was written before U2 ever existed. They never officially released it, they recorded it when they were teenagers and called themselves The Hype.

"They were probably 16 or 17, it's one of their first ever songs. You can hear where they were going with it though. It has that early punk angst that you would find in a teen band - but there are hints of where they were going with October in there also.

Gribbin said the majority of people involved in the film have close ties to the legendary band.

"There's a strong U2 connection with the team actually making the film. One of the producers was U2's agent when they first got signed, so they obviously know and trust him," he added.

He approached them saying they needed an early song for that first school gig scene, and they were happy to oblige.

The singer, who performs under the stage name Joe Echo, said that he hopes his version does U2 justice.

Killing Bono just been picked up by Paramount Pictures and is set for release in the UK by the end of the year.