While doctors feared he may never even walk again, the former SAS soldier focused on a photograph of the peak his father had given him as a child and became determined not to allow the bleak prognosis get in the way of his recovery.

"I had been parachuting in Kenya and the canopy split at 17,000ft. I literally fell out of the sky, " says the 32-year-old, who was christened Edward, but has been known as Bear for as long as he can remember.

"In the SAS I had lived through several life-threatening situations, but this was the first time I had been confronted with a real test of my will to survive. I felt powerless and vulnerable, but I realised the only way out was to have something to strive for and it had to be something pretty spectacular.

"When I was eight years old, my father had given me a picture of Mount Everest and as I lay in my hospital bed, virtually paralysed, I put it on the wall and vowed that one day I would climb to the summit."

Eighteen months later, he walked out of rehabilitation and, while his family may have wanted to wrap him in cotton wool, Bear remained true to his word and headed for the Himalayas.

He almost didn't return. During his first reconnaissance climb, an ice crevasse gave way. Falling 200ft, he was knocked unconscious and saved only by his team mate who managed to winch him to safety. For most, two near death experiences would have been a signal to lead a quiet life, but for Bear, who later this month will be speaking at an event in aid of the Yorkshire Air Ambulance, it was the start of a full-time career as an adventurer.

"When I came to, I was swinging like a pendulum on the end of the rope with hundreds of feet of sheer black ice walls on both sides, " he says. "It was terrifying, but made me all the more determined to push on. Ever since I have made survival my career."

Lying in a hospital bed, Bear Grylls, who had broken his back in three places following a parachuting accident, made a decision ; he was going to climb Everest.

Since entering the Guinness Book of Records in May 1999 as the youngest Briton to climb Everest, Bear has led a team across the North Atlantic Arctic Ocean in a inflatable boat, trained for the Foreign Legion, eaten dinner at a table suspended from a hot air balloon and become the face of Channel 4's Born Survivor series, which has so far seen him eating snakes and making natural mosquito repellent from a termite mound.

"What I've discovered is that things always don't go to plan, " he says.

"Sometimes things work out, sometimes I fall flat on my face. The key is to keep your sense of humour and always remain optimistic. Often the difference between death and survival is a little knowledge combined with a steely determination to survive.

"Last year when I was in Kenya it was an incredibly hot day. I was getting low on water when I spotted a herd of elephants. During my time in the Army I helped with anti-poaching operations and I remembered a ranger telling me that because elephants have such fast digestion, the water which comes out in their dung is practically sterile.

"After they had passed I picked up some dung, squeezed it in to my mouth and drank the juice from it. It was pretty disgusting, but it gave me more water than I had for the rest of the day

"I think the worst moment came in Australia's Outback. I was really hungry and found this fairly big python which I thought would make a great meal. But I knew as soon as I killed it, it would start to go off and I wanted to eat it in the evening. The place I wanted to set up camp was the other side of this big river so I held my tent in my hand and dived in.

"When I got in the water the python went mad and wrapped itself around my body. Thankfully I managed to fight it off and ended up killing it and eating it, so it was fine. People may say everything tastes like chicken. That's nonsense. A lot of wild food tastes bloody awful. There have been many times on my adventures when I yearned for a pile of salt and pepper."

While Bear's adventures have earned him a reputation as a risk taker, and he's been compared to Ray Mears and even the Milk Tray man on more than one occasion, he insists that behind the images of him biting the flesh off raw fish and skiing down impossible slopes, he admits that he is not completely immune to fear.

"This is what I was brought up to do, but of course there have been times when I have been absolutely bloody terrified, " he says. "Just a few weeks ago I was in the middle of the Amazon, lost, with no food and no shelter.

"It was torrential rain and I was sat there with my pants and trousers stuck to me. And I thought, 'Bear, what the hell are you doing?'.

"But the next day the sun came out, I made a bow and arrow and shot a load of piranhas in the river and had a great barbecue.

"That is all part of survival, it is about keeping your spirits up and using your imagination. It is like life in a nutshell, you have your ups and downs. Plus, I really thrive on it. The highlight of the series was when I came across a zebra that had been brought down by lions.

"I sliced raw flesh off the neck, it was still warm. The meat was so strong it was disgusting, like steak covered in mosquito repellent. But how many men get the chance to do something like that?"

When not pitting his wits against nature in some far-flung country, Bear, his wife, Shara, and their two young sons Jesse, 3, and 11-month-old Marmaduke, split their time between a house boat in London and a home on a Welsh island, and he admits fatherhood has tempered his adventurous spirit.

"I don't really like to do the big expeditions any more, I know there is always a good chance you won't come back, " he says.

"Shara always asks if I can do an episode in the local park or something. And now he is older, Jesse always cries when I leave. Walking away when he is in tears is without doubt a thousand times harder than anything else.

"By the same token, coming back is always the highlight of a trip. When Shara puts me in a bubble bath with the boys, she says, 'I wish people could see you now, they wouldn't think you were so tough'.

"I have seen so many friends who I thought were invincible die in climbing accidents or get taken by avalanches.

"If I have learned anything from this experience it would be that nature is the big boy and all we are doing is trying to live alongside it."

Bear Grylls will be speaking at Queen Margaret's School in York on April 21 at 6.30pm. All proceeds will go to the Yorkshire Air Ambulance and tickets, which cost £25, are available by calling 01347 888200.