The media are busy overloading when I arrive at Park Farm, Hugh Fearnley-Whittingstall's 66-acre slice of a stunning east Devon valley. Lots of people with walkie-talkies strapped to their waists are milling around looking tense and bored, and TV lights and cameras fill the interior of the collection of buildings at the foot of the valley, as the latest HFW Channel 4 food show is being filmed on an extremely tight schedule. The Observer photographer is also setting up in the ruins of the old barn that burnt down in February, and meanwhile there is a book signing that HFW is obliged to attend at one of the cooking courses run by his company.

A team of assistants tries to work out when best to fit me in, and I begin to suffer that sensation familiar from Hollywood movie junkets; the feeling of being one more dreaded appointment in a cram-full diary. I'm all ready for a prolonged wait when in walks HFW with a broad smile and a warm greeting.

The days of the wild-haired man of kitchen, with a reputation for cooking roadkill and a human placenta (although not in the same dish), seem to have been consigned to an earlier stage of his life and career. It's not that "Hugh Fearlessly Eats-it-all" has suddenly grown queasy about such delicacies; rather that perhaps he's reached a professional and personal maturity that's no longer best suited to headline-grabbing stunts.

The short-haired sleeker look that he's sported for the last year or so coincided with the celebrated carnivore's four-month experiment in vegetarianism a year or so back. That produced his bestselling River Cottage Veg Every Day! which OFM readers have voted their cookbook of the year.

"I'm thrilled about that, really thrilled," he says, looking convincingly thrilled. "I'm proud of the book because it's perceived as the blind spot of my cooking but it is actually the blind spot of British cooking: veg."

He continues on a long and engaging rant about how chefs have become lazily reliant on meat and fish, and how we owe it to ourselves, animals and the planet to eat more vegetables and less meat, and about the wonderful versatility of vegetables, and much else besides. A philosophy graduate, he has always maintained a metaphysical perspective on what we eat, seeing questions of food production and consumption as inescapably moral issues. As a consequence his books tend to be an enlivening cross between a menu and manifesto. It's never just a matter of getting the right recipe for mushroom ragout with soft polenta. He usually has an ethical case to make as well. "Call me power-crazed," he writes only half-jokingly in Veg Every Day! "but I'm trying to change your life here."

Some vegetarians may have blanched at the idea of a man with giant freezers full of his own slaughtered pigs waxing on about the importance of vegetables. But as someone who hasn't eaten meat for almost 30 years, I think a certain kind of vegetarian puritanism has led to a narrow-minded cuisine for decades. One of the joys of HFW's book, to me, is that he has rescued vegetables from vegetarianism.

But HFW has no wish to place himself in opposition to the bean curd brigade. "What I find tiresome is the vegetarian-baiting some of my well-known chef colleagues have gone in for," he says, not mentioning Gordon Ramsay. "I feel kinship with vegetarians. I think there's a greater affinity between conscientious carnivores and vegetarians than there is between conscientious carnivores and carnivores who frankly don't give a fuck where their meat comes from."

If nothing else, the book has changed the lives of his family. He says that they now have almost as many meat-free days as they do with meat. It was always his intention to eat less meat, and indeed he made the point explicit in the first sentence of his 2004 River Cottage Meat Book, in which he declared that we all eat too much of it.

Complete vegetarianism was never going to be a life-long option for a dedicated fisherman, hunter and pig-rearer. Instead he argues that what's important is to be "incredibly picky" about meat. He knows that people will claim this is an elitist stand. But he's not a man who is easily flustered by the facts of his privileged upbringing and considerable wealth.

"Of course it's easier to eat higher quality meat if you've got money," he says. "But there's no economic argument that makes it OK to be nasty to chickens and pigs, because we don't have to eat chickens and pigs at all."

That's true, but it's also true that not eating chickens and pigs presents several challenges. Eating out, for example, when so many cafes and restaurants offer dull vegetarian options. Another problem is eating in – specifically, what to do about protein when you can't face another lentil? Although HFW didn't set out to write a cookbook based on a carefully balanced diet, he does enough exciting things with beans and pulses to make you re-evaluate your feelings about chickpeas.

I ask him if he relishes the power to influence people's ideas about their food. He makes a bold attempt at a modest posture, suggesting that if there are "just a few people out there whose eating habits are changing, that's all the job satisfaction I need. If I'm not getting that, then maybe try something else".

Oh come on, I say, you know you're doing better than that. Look at the book sales, they can't all be bought as unread home decoration.

"No," he agrees, breaking into a great big schoolboyish grin, "but thank God that people do buy them for that reason. Let's not pretend that every one of them is dog-eared and covered in grease."

All I can say is that my own well-used copy of Veg Every Day! is well on the way to attaining exactly that look – except I'd prefer to say it's covered in extra virgin olive oil rather than grease.