At River Cottage HQ, just outside Axminster in Devon, on this freakily beautiful late September morning, there is not a breath of air in the whole valley to get the wind turbine moving, but the solar panels are already waking up to the early morning sun. Walking down the steep track to Park Farm, the 66 prime acres that Hugh Fearnley-Whittingstall bought five years ago to house his ever-growing brand, and put his philosophy of food into practice, you might find yourself humming harvest festival hymns or even Jerusalem. A dozen cattle are munching the green grass of home, fat sheep give every impression of life lived to the full. Chickens peck about under a thatched hen house and contemplate the prospects for the day. Smoke is rising from behind the two large-scale teepees in the farmyard where a new clay oven is being fired up, and a dozen fresh-faced employees at RCHQ are standing in a circle apparently hand-sifting its aromatic fuel, while talking about the weekend's parties. In the cottage garden a film crew from Channel 4 is moving among fabulous giant blown thistles and beans and curly kale and marvelling at the light. "What we want is a big bowl of that abundant stuff," a young cameraman is suggesting of a particular shot, and I can't help feeling he might be spoilt for choice.
In a flagstoned room of Farrow & Balled mismatched chairs around a long oak table, there are a number of crates full of empty champagne bottles. A tray of scones hot from the oven appears, and not far behind it the OFM readers' Food Personality of the Year himself, toting a bottle of just-pressed apple juice and a half-smile. Fearnley-Whittingstall has become a far sleeker figure than the familiar caricature of his early sweatier butcher's block and homemade jumper days. Most of the curls have gone, the specs look a touch more understated, and he is lean and long-striding and brimful of the morning. The new series of River Cottage is vegetarian and he has been meat and fish free for three months, so it is tempting to think his almost palpable healthy glow is down to the new diet. But he thinks it actually goes back a bit further than that.
"I'd love to be able to say that in three months I have lost a stone and have boundless energy and can now run the 100 metres in 11 seconds," he says, between mouthfuls of scone and sips of rooibos tea. "But it's not quite as simple as that. At the beginning of the year I had a cholesterol test and was concerned it was on the up. I'm someone who loves good cheese and who isn't shy of chewing the fatty bit off a decent chop, and I felt I had to rein it in a bit. And I also did something that I do once in a while which is to stop drinking. So I've had a bit of a cleansing year. And I lost some weight and then I went into the veg diet and continued to feel good."
Hasn't he been craving blood, or at least black pudding pilaff?
He says not, though his concession to his former lustily carnivorous self does allow him, when cooking fish or meat for his family that "if there is a nice bit of juice pooled up in the corner of a tray then I might dab a bit of bread in it". He cites the big fish heads he roasted for Sunday lunch from the Observer's photo shoot as his most recent temptation in this regard – "everyone was feasting on them with a bit of garlic and thyme and rosemary, the wonderful fish cheeks and the skin all crinkled up and crispy" – but generally he says he has found his abstention from flesh a bit of a liberation, even, at 46, a sort of coming of age. "I would have found it very hard to do 10 years ago," he suggests, "and not seen the point of it. But it makes sense for me right now. I'm not suggesting that everyone should give up meat and fish for three months but I am suggesting that everyone should certainly have days when they don't eat any. The fact is, if we are going to get in tune with what is good for our bodies and our planet then we must have days like that."
The book of the series – River Cottage Veg Everyday! – is already out and at the top of the bestseller lists but he has been amused by the "one or two letters in the Guardian that have sniped about how the great meat eater has suddenly turned vegetarian". To him, he suggests, there is nothing Damascene about it. "I mean the opening line of my 500-page book about meat was 'We all eat too much meat'. My point was always that we need to treat meat with far more respect and approach eating it in a holistic way. It is something we all know, I think, in our heart of hearts. We know that the scale on which we are killing animals and pushing them through factories and turning them into burgers is wrong on some basic level. And we probably feel it in terms of our health. It is odd that it is so easy to change that, but that we resist doing it. The change is a simple one: eat more veg."
Part of Fearnley-Whittingstall's ever greater aura of evangelism no doubt derives from the success of his current campaign over European fishing policy. He is a devotee of the idea of stark life-changing moments, and his own, in this respect, came almost exactly a year ago on a trawler in the North Sea while researching his polemical Hugh's Fish Fight series. "I knew in theory quite a lot about the world of industrial fishing," he says. "But actually going out there changed everything. We had quite a wide agenda for the series to start with. But within 24 hours of getting on this Scottish trawler we watched them discarding all these amazing fish because of quotas and it really hit home."
He'd imagined that the complexity of fisheries legislation might make a campaigning programme about fish quite difficult compared, say, to his battery chicken protest, but talking to the trawlermen and realising that although they were legally obliged to throw fish away they knew every day it was "very, very wrong" he saw immediately the battle cry. His producer Will Anderson suggested that instead of just filming the conveyor belt of fish going over the side they actually collected all the fish that were discarded in a single haul. In the end there were 22 baskets of prime fish on deck. The parable was almost biblical. "I had already agreed that I would cook for the crew that night," Fearnley-Whittingstall recalls. "So we saved a couple of beautiful fish out of those discards and cooked them up. The fishermen ate a lot of fish. But even so we calculated if I cooked that dish with all the fish we had thrown away I could have fed 2,000 people. From one haul. Then you have to multiply that by all the boats that go out. And suddenly you get the sense that the estimate of half a million tonnes of wasted fish, or of as much fish being discarded as being used, starts to ring true. We went to bed knowing if you showed that to people at home they would immediately see the madness of it."
And so it proved: 750,000 people have signed up to the campaign to end discards and it has, after fierce lobbying, been adopted in the draft of the new European fisheries policy which is expected to come into force in 2013. Fearnley-Whittingstall is keen to stress that it is not the end of the road – "that will only come when we are eating fewer fish and the numbers in the sea are growing" – but it should prove a significant step forward.
For all the literal cottage industry of much of his work, this type of large-scale environmentalism has always been an ambition of Fearnley-Whittingstall's. You could certainly trace a dotted biographical line, he says, from this campaign back to the year he left Oxford when he set off for Africa with a friend and an aim to write a book about the efforts to save wildlife in the sub-Saharan continent (as well as about the "messiah complex" of certain conservationists who believed they had all the answers).
He traces some of that ambition back to university and the philosophy part of his PPE course. "I really liked doing moral philosophy at Oxford. I continued to read a lot of that afterwards. I always think my final thesis from my philosophy studies was the introduction to my meat book."
The son of a mother interested in ecology and local politics and a left-leaning advertising creative father, he had always been a man in search of a cause. "Back in the 80s we were quite a moralistic bunch of students," he says. "There was the anti-Thatcher thing and lots of my friends were handing out the Socialist Worker." Fearnley-Whittingstall felt common cause with striking miners might be a stretch for him. "I really thought, look you went to Eton and you have a double-barrelled name. If I was going to be involved in that sort of activism it would have had to be quite extreme to get over that – throwing rocks at the police or whatever. I had a credibility gap."
Having gone to Africa in search of ways of closing that gap, he suggests, he found a way to do it when faced with the politics of food provenance. While working at the River Cafe he was struck by the passion of some of the farmers who supplied meat, and quickly he saw that their arguments to do with welfare and sustainability were a continuation of those he had encountered in Africa, on a more local scale.
Given his current campaigning success – and the career trajectory of certain Etonian contemporaries, the prime minister and the mayor of London among them – I wonder if a move into conventional politics is a possibility. He thinks not, and suggests he is not in contact with any of his politico peers, except Boris "through Rosie Boycott", though he would know "how to get in touch" if he wanted to lobby on a certain issue.
His own lifestyle is still the most powerful political statement he can offer, he believes. "The fish campaign has a harder edge focus than a lot of what we have been doing. But I also feel that in 15 years of the River Cottage we have managed to chip, chip away at certain issues – farmers' markets and provenance and even growing your own stuff. And I'd like to think a percentage of our audience behaves a little differently toward food than they would otherwise have done."
And how I wonder, with the sun streaming in illuminating his face, and him getting a bit fidgety to get on with his day's filming in the elysian valley outside, does he guard against messiah complex himself?
"I guess you need to keep a sense of perspective and be prepared to accept limitations," he says, with a grin. "But you also have to remember that you have a small window to get these issues across in, and sometimes you have to shout as loud as possible ... "
The award for best food personality is sponsored by Weber.