Chris Lemons was fairly new to saturation diving when he descended into the North Sea, preparing to carry out routine maintenance on an oil well.

Flanked by experienced diver, Dave Yuasa with mentor Duncan Allcock acting as bellman, the pair descended into the depths, unaware of the drama that was to unfold on the seabed.

Tethered to the diving bell together with their umbilical cords, which deliver breathing gas, hot water to keep warm, light and electricity for their cameras, the pair set to work.

But unbeknownst to them, the positioning system had failed on their dive support vessel 100 metres above them and was now drifting out of control, away from the dive site.

Dive supervisor Craig Frederick immediately instructed his divers to return to the safety of the bell, as the ship drifted further away.

Yet Chris' umbilical cord was snagged on the structure the pair had been working on, and as the full weight of the 8,000 tonne ship strained against his lifeline, his umbilical started to stretch.

"Like a shotgun, it snapped and it disappeared into the darkness along with my fellow diver Dave who had been trying to get back to me and help me, but because he was being dragged away by the boat, was unable to," recalls Chris.

"Suddenly I was falling backwards onto the seabed, in complete darkness. I had a gauge which told me how much gas I had but it was that dark I couldn't even see it.

"It was probably a good thing in retrospect, it would have been panic-inducing seeing how much I had left."

As Dave climbed back to the safety of the bell, Duncan pulled on Chris' umbilical chord. As he pulled up the broken, tattered end of the gas hose, Duncan shouted: "I've lost my diver, I've lost my diver!"

With access to just five minutes of back-up gas, the crew knew Chris had little chance of survival.

As the crew and divers above the water began their frantic search to find Chris, he began to scramble around on the seabed in a desperate bid to survive.

"I fumbled around in the darkness and I was very lucky to bump into the structure," Chris recalls.

"I could have very easily turned around and walked into no mans land. That was one of many doses of good fortune."

It quickly transpired that the boat was some 200m away and Chris quickly became aware of his own mortality.

"I was in the strange position where it dawned on me quite quickly that there was no real hope of me getting out of the predicament," he says.

"I was in the unusual scenario of thinking about my impending death essentially.

"You feel desperately sad and a great deal of disbelief when you find yourself in that strange situation.

"Suddenly you're there about to die in the depth and the darkness of the North Sea."

Chris says he could "sense the end was coming" as it became harder to breathe, hoping that death wouldn't hurt. And then he says, he felt "nothingness".

What happened next is the subject of Last Breath, a film based on Chris' true story of being stranded in the North Sea.

Due to be release on April 5, the film has access to the archive of footage which was shot on Chris' own diving suit and on a remotely operated vehicle which was also in the war.

The film also tells the compelling story using reconstructions and interviews with Chris' colleagues.

Director Alex Parkinson said: ''What [Chris] went through is something everyone can relate to and it's this true horror of being in the dark and cold and pitch black and it's the story of the people around him trying to save him."

Chris says that the entire incident was perhaps much more traumatic for his colleagues than himself, as they watched his twitching body on the seabed via cameras as they raced to his rescue.

"When you watch the full footage, you realise 30 minutes is an extremely long time and they would have naturally assumed the worst," he says.

"Despite having fairly lucid memories of it all, it still seems strange to watch it."

The film, which will be shown across Scotland, recounts a remarkable tale of the human spirit in the face of enormous adversity.