It's a crisp January afternoon, and Fergus Drennan is picking mushrooms in a field near the Kentish seaside town of Whitstable. Out of the corner of his eye, he spots some black and white feathers poking up from a tuft of grass.

"A bird!" he shouts. "It's not even been dead that long; you can tell from the rigor mortis. It's so cute, isn't it? Come on... come back to life... No. It's definitely dead. The only question is... why?"

Fergus looks up. Above him run several power cables. The bird must have been electrocuted. This is excellent news: since our feathered friend didn't have a nasty disease, Fergus says it's safe to eat.

Welcome to the eccentric world of a culinary pioneer. Drennan, 35, is a full-time forager, environmentalist and star of the recent BBC programme The Roadkill Chef. In a world of food miles and factory farming, he's like a breath of the fresh air rolling in off the sea.

Everything Fergus eats is sourced directly from the British countryside. If you can pick it, gather it, or peel it from a patch of Tarmac, Drennan will tuck in. Kent, the garden of England, is also his supermarket.

Later that day, he rustles up dinner. The bird, a common wader called a lapwing, is served with chopped mushrooms in a home-made ravioli. On top, we have tomato sauce and wild spinach from a local layby. For pudding? Sorbet made from seasonal berries.

It's all quite delicious. And, more importantly for Fergus, the meal was provided at a negligible cost to the environment. Foraging isn't just fun, he says, it's green as well. No food miles, no pesticides, no pointless plastic packaging.

Eating roadkill is also an ethical exercise. Drennan describes himself as a vegetarian, saying he's got "issues" with animal husbandry, and won't eat creatures that are raised for slaughter. Ones killed by accident on our roads, though, are "just another resource".

Foxes, he says, are best pot-roasted in red wine, with wild mushrooms. Badger, a more intense flavour, goes well in burgers. Pheasant and rabbit can be done any way you like. Together, mangled mammals and birds make up five per cent of his diet.

"One of the few things that I tend to avoid are cats and dogs," he explains. "In theory, I'd have no problem with eating them. But they've always got name tags on their collars, and since I have two cats, it's a step too far.

"The only other thing I haven't enjoyed was an owl. Once I found a dead little owl and a dead barn owl. One was nice, but the other was vile. It tasted of urine. I was very surprised: until then I'd always been able to eat anything. I don't know, maybe it was diseased."

Drennan is on a mission to convert Britons to his way of thinking. In The Roadkill Chef, he attempted to change the people of Sandwich's junk-food diet by serving foraged food and roadkills to customers of a local pub (it met with mixed success). More regularly, he runs foraging courses.

"I love foraging," he says. "It's so peaceful and it's so sociable, and I love to be able to give people another dimension to the way they live. After I've taught them, they can go out in the fresh air, and it's not just about walking the dog."

Across Britain, foraging is booming, as consumers grow savvy about the sourcing of their food and the benefits of a seasonal diet. The TV survival expert Ray Mears' latest series, Wild Food, in which the rotund forager attempts to eat like a prehistoric Englishman, has been a ratings hit.

Professional foraging is also catching on. Drennan estimates that around 50 pros make a living supplying the restaurant trade. And if you count the people working for them, he says, it's "in the hundreds".

Until 18 months ago, Fergus was one of them, running a business supplying top-end London restaurants including The Ivy, J Sheekey, Moro and St John. But he quit, and now claims to have "a big problem" with the sustainability of the trade.

"I was making �250 profit a week, which was pretty good," he says. "But the reason I love foraging is this slowness - when I was picking to order it became just another job. It was labour-intensive, and I think that threatens some species, particularly fungi. Also, I worried about how eco-friendly it was driving up to London each week."

Drennan isn't the only one to have problems with professionals. In November, Hampshire Police prosecuted Brigitte Tee-Hillman, 64, after the Forestry Commission complained about her picking mushrooms in the New Forest and selling them on to restaurants.

After 32 court appearances, one charge of theft, and another case involving the right to pick on public land were thrown out (a judge attacked the waste of public money) and Ms Tee-Hillman was granted the right to continue collecting fungi for the rest of her natural life. "At least it means the Forestry Commission won't always be watching me when I have a pee in the forest," she said.

Back on the Isle of Thanet, Drennan runs an advisory service on his internet site wildmanwildfood.co.uk. It helps identify species of plants, particularly potentially dangerous mushrooms, and also advises on "foraging and the law", which mostly revolves around rules concerning trespass.

The area close to his home town of Herne Bay is ideal foraging country thanks to the variety of habitats. There are beaches and cliffs, salt meadows and ancient woodlands.

"It's the best place I've lived since being at university in Lampeter," he reckons. Down at a local seaside spot he calls Botany Bay, beneath white chalk cliffs, we pick a basket of seaweed to make soup, his staple diet during winter. Fergus hops exuberantly over rocks, occasionally losing a trainer in a rock pool, or splashing salt water on his anorak.

"I'm a big t'ai chi enthusiast, and it's amazing how often I use those moves when I need to duck under a tree trunk or something."

We pick sea lettuce, kelp, dulse, and laver. "Not all seaweed's edible," he explains. "Some produce sulphides and bromides, or soak up radiation. But this lot is great for eating. I'll make a massive pot of soup, which I'll keep in the freezer. It's incredibly healthy, and gives you a real glow."

Fergus is passionate about plants, and has an extraordinary eye for edible titbits. "Stop the car!" he screams, as we motor down a secluded lane.

What is it? A dead badger? "No, I've just spotted a load of charlock, a leaf from the cabbage family, in the verge. Oh, and look: a load of wild carrots."

Nothing, it seems, is off the menu. Not even slugs.

"When I was at university I got so many slugs. Fried them, blended them and stored them to rehydrate. It was like mince."

Later, we find several kilos of field blewit mushrooms that would fetch a fortune in your average deli. And of course, there is the recently-deceased lapwing, which Fergus pops into his pocket before skinning and disembowling it in the sink at his parents' home in Herne Bay.

"I never leave a thing," says Fergus. "I'm even experimenting with fox skin for making drums.

"I was inspired by Kalahari bushmen , who use the bladder of some kind of antelope for a pouch to carry water water. How far removed is that from your horrible supermarkets?"

How far indeed. And as we say our goodbyes, Fergus quotes a Lakota Sioux proverb: "You search until you find the plant you want, but you do not pick it. You must continue until you find the next cluster of the same plant. Only now can you pick, so ensuring that no plant will become extinct through over-harvest."

Or, as the Brits might say: "happy foraging!"

Pan-boiled fox

Serves 6 to 8

INGREDIENTS

2 large onions, roughly chopped
boned or on-the-bone legs of one medium-sized to large fox
6 medium-sized carrots
6 medium-sized courgettes
1 cup olive oil
2 bay leaves
4 to 6 whole peppercorns
2 to 3 pieces of allspice
2 to 3 lemons
2 large eggs, beaten
sea salt and ground black pepper

TO COOK

In a large saucepan gently brown onions in olive oil. Add meat. Add bay leaves, allspice, peppercorns, salt, ground pepper, juice of one lemon, carrots and a few cups of water. Cover and simmer for 30 minutes. Add courgettes. Cook for another 30 minutes at a slow boil. Mix eggs with remaining lemon juice. Ladle offliquor from the pan and beat in with the eggs. Return to pan. Serve with hunks of rustic bread.