This is Ant and Dec's first starring movie role

The pair, who together host Saturday Night Takeaway and I'm a Celebrity... Get Me Out Of Here!, star as best friends who fake a film about an alien.

They spent one and a half hours signing autographs and greeting fans outside the Odeon Leicester Square ahead of the gala screening.

"We've seen Tom Cruise do it so thought we should too," said Declan Donnelly.

They both said they believed in extra-terrestrial life.

Roswell hoax

Ant McPartlin said: "Obviously there's some kind of life elsewhere. I don't know whether it would look like anything we recognise but I do believe in aliens."

Among the guests at the premiere were Girls Aloud singers Cheryl Tweedy and Kimberley Walsh, TV presenter Denise Van Outen and actress Minnie Driver.

The two men the film was based on, Gary Shoefield and Ray Santilli, were also there to see how their story had been portrayed on screen. They produced a hoax film of the Roswell alien autopsy to fool UFO enthusiasts.

This was Ant and Dec's first starring movie roles, having had cameos in Love Actually.

"Obviously we were really nervous about doing it but thought that if we're going to take risks and challenge ourselves, then this is the film to do it because we really believe in it," said McPartlin.