Sir Peter Jackson's WWI documentary They Shall Not Grow Old premieres in London

Sir Peter Jackson's latest creation, They Shall Not Grow Old, has premiered at a red carpet event at the London International Film Festival.

The premiere was attended by dozens of VIPs, including Prince William, Duke of Cambridge, Shaun of the Dead filmmaker Edgar Wright and Lord of The Rings star Dominic Monaghan.

The premiere marks the end of a four year journey for Sir Peter, which saw him and his team painstakingly transform 600 hours of never-before-seen black and white World War I footage into sharp, detailed, colour video.

They Shall Not Grow Old is part of the centenary commemorations of the war, and was initiated by the Imperial War Museum in London, which head-hunted Sir Peter.

"They came to me four years ago and they asked if I'd be interested in doing a documentary on the World War I using their archive footage in a unique and original way. There was no other brief - it could be anything I wanted it to be really," Sir Peter told Newshub.  

"We did some experiments with how it can be restored and I had a vague imagination of what might be, but then we got it and it so surpassed anything we thought it might be."

Much of the work was done at Sir Peter's studios in Wellington, in collaboration with Stereo D, a Burbank and Toronto-based video conversion studio.

Stereo D's Head of Post Production Milton Adamou summed up the difficulty of the project: "It's bloody hard".

"All of the processes had challenges, particularly the restoration and colourisation because we hadn't done it before, certainly not on this scale," he said.

Much of the footage is confronting, with dead bodies, blood and horrific injuries featured.

"War is gruesome. People get killed in wars, unfortunately, and it’s important not to sanitise it," said Sir Peter.

"Sanitising war sends the wrong message to younger people, especially the video game generation who need to know the consequences are awful and when people bleed, they bleed a lot".

Monaghan, who played Merry Brandybuck in the Lord of The Rings trilogy, attended the premiere as a friend of Sir Peter.

"I'm here to support Pete. I love Pete and I was in London," Monaghan said.

"He's an extraordinary filmmaker and he's always had an interest in World War footage. He's very sensitive, so it's a great marriage for this subject."

It's a marriage Sir Peter is hoping ensures the sacrifices of the Great War are never forgotten.