Frankly, I have been brought here under false pretences. I had been promised an interview with Ray Mears in Richmond Park. We would pitch a tent (no doubt illegally), make a fire, shoot a few deer and spend the afternoon eating venison and shouting abuse at posh passersby in green wellies. Somehow this has been transmuted into an hour with Mears at his publishers in central London, in an anonymous office on the 14th floor. I cheer up momentarily when I spot a labrador, but it belongs to his publicist. The only concession to his reputation as Britain's guide to the Great Outdoors is that he is wearing a pair of stout hiking boots. Ideal for the Euston Road.

The urban setting is not entirely inappropriate, because Mears is surprisingly urbane. It's hard to imagine him wrestling an alligator, or even a labrador. He is friendly, podgy, earnest. Fifty next year, he has decided to mark the occasion by writing his autobiography, which is not the expected tale of derring-do but the unlikely story of an only child born in suburban south London who became obsessed by wild places and devoted his life to them.

Fifty must be a watershed in the deer-skinning, alligator-wrestling business. Is he trying to tell us something with the memoir? "I've got a lot of miles on the clock," he admits. "The body doesn't do what it could do and it's probably time for an oil change, but hopefully you get wiser. You get to a point where you can look out and enjoy the view because you're not having to climb the ladder so hard."

The book is an unvarnished account of what he insists is an accidental career as a TV presenter. "I didn't seek out what I do. It found me. I was in the right place at the right time for certain doors to open. I didn't have to use a crowbar to force my way into the world of television." He was, though, a man on a mission with those early BBC series – Tracks and World of Survival. "I was trying to put right the damage done by Rambo. Everyone thought of this word 'survival' as aggressive, militaristic and rather stupid if you ask me. I wanted to show that this knowledge was healthy, and I think I've been able to achieve that."

Mears dislikes the term "survivalism" and balks at people calling him a "survival expert". "I can't understand people preparing for disaster," he says. "We should be preparing to enjoy life in the world. That's not to say there aren't survival skills in what I do, but that's the shorthand of a much bigger and more beautiful subject." The term he prefers is "bushcraft" – the art of understanding and being at one with the natural world. "You learn the value of the things around you, and that forever changes your perspective on nature. It makes you feel at home in places we are otherwise brought up to believe are threatening. That's one of the things I really object to in television – this constant rhetoric that wild places are inherently dangerous. They're not. They're fine. It's just whether you do the right thing or not."

The other thing that annoys Mears are telly stunts – the I'm A Celebrity …Get Me Out of Here approach to the natural world. "In recent years the lines between entertainment and documentary have been blurred," he says, "and that's a mistake. People now don't trust what they see on television." Mears, who generates most of his own ideas for TV series, also complains that budgets and shooting times have been reduced since he began in the early 1990s, and that you have to fight to be truthful. "I had a big argument recently with a producer who wanted me to walk across a sand dune to give it scale. But I said: 'You just don't do that. You don't go trekking through the desert like in Lawrence of Arabia. It's ridiculous.' I can't stand artifice and don't think it's necessary. That's poor film-making. It's better to tell the truth."

In 2009, after making programmes for the BBC for 15 years, Mears did a series for ITV, and has since made two more. Why the switch? "People think either that they weren't offering me enough money or that I'd had some sort of spat. But it was neither of those things. The BBC were slow to make decisions, and I was critical of some of the management there at the time, but none of these were the reasons I went to ITV. ITV simply asked me to make some wildlife programmes. I love wildlife, it was a natural thing for me to do, so I said yes, and I really enjoyed them." He will be back on BBC4 next year, though, with a series about the Wild West, and says ITV have no problem with that. "The management at ITV is very grown up," he says. "Having run a business for 30 years, I feel I can have a business conversation with people who really understand and that's been refreshing." BBC, take note.

Mears in his 2010 ITV series Wild Britain with Ray Mears. Photograph: ITV

He hopes his programmes have encouraged us to become more environmentally minded, but reckons we have to become more hard-headed in our approach to conservation. He warns against the danger of "loving something to death" – not being willing to cull individuals to save the species. "In Britain, with wildlife, we do need to maintain balance," he says. He mentions a magnificent beech tree in Ashdown forest, close to where he lives in Sussex, which needed pollarding. Local people loved it too much for its branches to be cut, and eventually the tree collapsed. "If it had been pollarded 20 years ago, it could have gone on for another 600 years." Given current rates of population growth, he says, we have to get a lot smarter about conservation, or we will be responsible for "one of the largest extinction episodes in history".

Mears's career is usually seen as a counterpoint to that of Bear Grylls, ex-soldier, action man, out-and-out survivalist, the sort of Rambo figure Mears has set himself against. "We come from different genres and got played off against each other," says Mears, "but I don't have any problem with him or what he does, and since I've stopped playing ball with the press others have been paired off against him. That's just the way the press works. The only objection I have to what I've seen him do is that some of the things are crazy – leaping off cliffs into water when you don't know what's in it. If a 15-year-old was to copy him and impale himself on a pram leaping into a canal somewhere in Britain because they were inspired by it, I would think that was his fault. It goes back to my feeling about the social responsibility of film-making."

One chapter in his book deals with the role he played in tracking gunman Raoul Moat in woodland close to the village of Rothbury in Northumbria in July 2010. His involvement was revealed at the time, but Mears says he wanted to have his say because he felt he had been accused of muscling in on the police operation for publicity purposes. He says the police had requested his help in tracking Moat, and that he did everything possible to keep his involvement secret. At one point during the search, he reckons he got within 20 feet of Moat, who eventually shot himself after being cornered by police.

"It was important to me that the truth was told," he says. "I'm a tracker and if you have that skill, you are duty bound to make it available. I'm very glad to have been able to help. The whole event was a tragedy, and there was no glory-seeking. It was a very difficult thing to do, but, being in television, people don't trust you. The media criticised the police for having involved me." He is wary of the press, and highly critical of the way it covered the Moat saga. "What I saw of the press during that episode was a disgrace," he says. "The net result is I would never trust 24-hour news coverage again."

In some ways, Mears the earnest, private man is not far removed from the small, self-contained boy who spent much of his childhood camping out on the North Downs. "My parents moved to Kenley, which was a very green place," he recalls. "There was a local common and, because it was chalk downland, there were wonderful plants, wonderful wildlife, woodland I could get lost in and explore, and that's when the bug really caught me. If you want to go off and explore wild parts of the world, the best way is always to do it progressively. Big journeys start with little journeys in the parks and common land, your confidence grows, and as your confidence grows the trails grow longer."

Mears helped police track fugitive killer Raoul Moat in 2010. Here a sniper scans the Northumbrian countryside. Photograph: Owen Humphreys/AP

The fact that he was an only child was significant. "I'm very happy in my own company, and I like being alone in the wild. Being alone means there are fewer disturbances, so you see more. Not everybody is suited to travelling on their own, but I'm happy to listen to my internal voice. If there are lots of you, there are lots of rocks going into the pond, and lots of ripples going out, but I like to just be the rock that's quiet in the pond and see what comes to me."

I'm not sure this metaphor quite works, but it's a useful indication of Mears's view of the world. He did a lot of judo as a teenager under the tutelage of a gnarled, stoical second world war veteran, and imbibed its philosophy. "It's a very profound thing. The first thing you learn is that it means 'the gentle way'. People always say there's nothing very gentle about judo, but there is. It's the concept of taking somebody else's strength and turning it against them using your skill and your intellect. It teaches you spirit and determination. You learn there's always somebody bigger than you who can beat you, so there's a degree of humility. It's a very grounding experience. Every day it helps me in some way."

Mears loves silence and says we are losing our ability to connect with it. "I'm lucky to have been able to spend a lot of my life in places where there is virtually no noise pollution, and when you come home it's staggering how much noise there is. The sound of nature is important. I'll sometimes sit in the woods and listen to the wind in the trees. I can identify the different species of trees by the sound their leaves make, and they can foretell weather changes."

Mears didn't go to university and the career he aspired to in the Royal Marines was thwarted by poor eyesight. Instead, he read voraciously and taught himself about bushcraft, seeking out experts and badgering them to pass their skills on to him. He worked in the City briefly, but chafed at the constraints and started running bushcraft courses and developing a career as a photographer of the natural world instead. That led on to books and, from the early 1990s, television. He abandoned his career as a professional photographer, but it remains a passion and he is clutching a portfolio of recent pictures when we meet.

The most affecting part of the book is the section dealing with the death from breast cancer in 2006 of his first wife, Rachel, which left him angry, bitter and confused. "My stock-in-trade is fixing problems, but I couldn't fix this one," he says, "and that challenges your personal philosophy." It caused a huge personal upheaval and fallings out with others close to him. "You're coping with the most poisonous cocktail of emotions," he says. "That's one of the sad realities of the experience."

He remarried in 2009, has a teenage stepson, and continues to combine TV work with books and, his original pursuit, teaching bushcraft. His company Woodlore has been going for more than 30 years, and he is as much entrepreneur as environmentalist – he a sideline selling outdoor clothes and equipment online. He stresses that when he is running courses, including an annual expedition to the Arctic, he is the antithesis of the celebrity. "I'm a different person on the courses, and sometimes that's a shock for people. I teach properly, and what I don't like is people who come on a course just because they want to meet me or take my picture."

When Mears is through with me, he has to go to Broadcasting House to record Desert Island Discs. I think it's fair to assume he will be able to cope with life on the desert island, and will quickly turn it into a smooth-running commercial operation. Just don't try to rescue him. He will be in paradise, listening to the wind in the trees and communing with the ghosts of the hunter-gatherers he admires so much.

My Outdoor Life: An Autobiography is published by Hodder & Stoughton (£20).