A pair of highland ponies nibble grass as two kestrels swoop across the path. Up a rock face across this windswept valley deep in the Scottish highlands, a golden eagle is hunting for prey, its movements tracked by a GPS tag. Nearby are Scottish wildcats among the bracken – Europe’s rarest cat, with fewer than 400 left – plus red squirrels, black grouse, the occasional pine marten, shaggy highland cattle adapted to the harsh environment here, and, like much of the highlands, plenty of deer. Wild boar and moose roamed this corner of Sutherland until recently.

But if Paul Lister, the estate’s multimillionaire owner and the heir to the MFI fortune gets his way, two species not seen on this land for centuries could soon be added to the list: wolves and bears. Alladale estate, which Lister prefers to call a “wilderness reserve”, is one of the most ambitious examples of so-called “rewilding”, the banner under which a growing number of people are calling for the reintroduction of locally extinct species to landscapes. Bringing back species such as wolves, beavers and lynx, rewilding advocates say, can increase the diversity of other flora and fauna, enable woodlands to expand and help reconnect people with nature.

The unofficial figurehead for this movement, the outlines of which will become clearer with the formation of a new charity early next year called Rewilding Britain, is Guardian columnist and author George Monbiot. His book Feral, published in 2013, has been reprinted over 30 times in hardback and has led to a national debate over the merits of restoring the country to a wilder state.

“For me, it’s part of a wider effort to develop a positive environmentalism, which we desperately need,” says Monbiot. “[It’s about] creating a vision for a better world that is much more appealing than just laying out what is wrong with the current one, of having a rather more inspiring one than saying, ‘Do as we say and world will be a bit less crap than it could be’.”

Facebook Twitter Pinterest European bison ( Bison bonasus) at Armenis, Tarcu Mountains, southwestern Romania. They were brought to Armenis in May as part of a rewilding project. Photograph: Bogdan Cristel/Reuters

While rewilding efforts on continental Europe have seen substantial progress – Eurasian beavers are now found in 25 countries, European bison have returned across eastern Europe including one of the biggest reintroductions in Romania this May, and wolves have spread across much of Europe including Germany, France and last year one was even found in the Netherlands – in the UK there has been more talk than action. It is a charge that even Monbiot admits is not unfair, but he argues: “Talk precedes action.”

One area where rewilding efforts in Britain have made some modest progress, albeit at very local levels, is in native tree-planting. In a Cumbrian valley, the Wild Ennerdale project has seen conifers for forestry replaced with native broadleaf species whose populations have dwindled. Knepp Castle estate, in West Sussex, has been planting relatively rare native black poplars as part of its rewilding efforts. In just over two decades, Trees for Life in Scotland has planted 1.2 million trees, mostly Scots pine, and plans to reach its second million in the next five years while diversifying into other species including aspen.

Trees could be helped further by returning wolves and other top predators to Britain, Monbiot says, because of the knock-on effects of such “keystone” species. One of the most famous case studies is the return of wolves to Yellowstone national park in the 90s, which have been credited with moving deer around, meaning less damage to new trees, allowing them and other vegetation to grow, stabilising the soil along river banks.

In Scotland, deer still pose a serious threat to the 600,000-odd trees that Lister has planted in the glens at his estate and the hundreds of thousands more planned, even though the management has already culled deer numbers by 50% over a decade, to around 600. Wolves would not only reduce those numbers further – they specialise in killing deer – but would be a tourist attraction too. “We’ve managed to put a man on the moon, I don’t see why we can’t get wolves back in Scotland,” says Lister. Bears would also learn to specialise in killing deer, he believes, and would be an even more dramatic pull for visitors than wolves.

Paul Lister who has introduced wild boar and elk on his estate at Alladale, Sutherland, Scotland. Photograph: Alamy

But Lister’s plan does not extend to allowing these carnivores completely off the leash. “I’m not an advocate of reintroduction, I’m not a supporter of letting these big animals out in the freedom of the countryside, because we’ve sanitised our landscape so much I don’t think there’s enough tolerance of these animals for us to be coached through the whole process.” Instead, Lister wants to fence in land at Alladale and on neighbouring estates to release two packs of around five wolves each, plus bears, which he says would be a huge pull for day visitors to the estate, generating jobs for locals through increased demand for B&Bs, work on the fence and ecology roles.

But the idea of fencing-in such a large tract of land raises hackles with hikers, who have a legal right to roam across the estate. “Our view is that it’s not a reintroduction that he’s trying to do, he’s trying to create a giant zoo,” says Dave Morris, director of Ramblers Scotland. “We’ve always resisted this, saying it would be inappropriate to fence in such a huge area of land, and it would have big landscape impacts, as you’d have to have a road all around it.”

Privately, some rewilding advocates express concern that Lister’s uncompromising style could set back support for rewilding. Some people living near Alladale are not convinced yet either. One householder, who did not wish to be named, told the Observer: “Is he still on about that nonsense? What if the wolves break out? We worry for our son [who has sheep]. We had a meeting about it. It was pointed out to him [Lister] that if it was covered by the snow, the wolves would get over the fence. We might get a wolf on our doorstep.”

Finlay Collouch, a neighbour who said he supported the estate’s tree-planting and outreach education with local children, said of the wolves plan: “It doesn’t put me up nor down if they do it, as long as they keep them there. But I don’t see how they’re going to keep them there [because of the snow drifts going over fences].”

Alladale’s man on the ground, Innes MacNeill, the reserve manager, says he cannot see how it could happen without a fence, because farmers would shoot wolves if they were reintroduced straight into the wild. “The fence is probably one of the things we need to overcome. Ultimately the general public have to want this, they have to want something different, something that would hopefully be really special.”

The return of the wolf, however, could be eased by the reintroduction of a far less controversial species. Jamie Wyver is a masters student at Imperial College London looking at public attitudes towards the reintroduction of the lynx in the Scottish highlands and Forest of Dean. “The interesting thing about the lynx is it’s almost like we’ve forgotten about it. It doesn’t feature in nursery tales. It just gets missed off. It might be because they’ve been gone for a longer time [than wolves and bears] but it’s probably because they’re not a threat to humans. There are no records anywhere in Europe of anyone ever being attacked by a lynx,” he says.

Facebook Twitter Pinterest A Eurasian lynx in Bavarian forest, Germany. Photograph: Christoph Bosch/Alamy

Wyver says most people he has spoken to know so little about the Eurasian lynx (Lynx lynx), which is still present in much of northern and eastern Europe and some southern European countries, that they often first think he is enquiring about the deodorant rather than the carnivore. Lynx could be back in the UK as soon as 2025, thinks Alan Watson Featherstone, the founder of Trees for Life. “The big picture is there are far too many deer in Scotland for the habitat. The next crucial step is to get a predator back, because that ecological level of top predators is missing. The wolf is not the one to begin with, because it comes with tremendous prejudice: the Three Little Pigs, Red Riding Hood; it gets the works thrown at it.

“We’re promoting the lynx as a more feasible candidate for reintroduction, it’s a solitary animal, an ambush hunter, it’s quite secretive,” says Featherstone, who believes that restoring enough habitat – in the shape of native woodland – is crucial to help such species come back. The lynx, he argues, would give people the experience of living again with a carnivore, and make a wolf reintroduction many years later more realistic.

Hundreds of miles south, in a forest on the west coast of Scotland, one species is already getting its teeth back into the UK landscape four centuries after being hunted to extinction for its fur. Four families of European beavers (Castor fiber) have spent the last five years in an official captive trial where they have successfully produced young (known as kits), built lodges and dams, in one case causing a freshwater loch to grow up to five times in size as a result.

“In some respects, it’s no great surprise – beavers do what we expected beavers to do,” said Simon Jones, head of major projects for Scottish Wildlife Trust, who oversaw the Scottish beaver trial at Knapdale, in Argyll and Bute. “But the whole point is that it’s not just about species reintroduction, it’s about what beavers do. Beavers create good habitat for other species – where you get beavers, you get good biodiversity. That’s not necessarily what our trial was about, but the wider drive in the wild for considering them is that the science shows amphibians, otters, waterfowl do well [as a result], because beavers are this keystone species that creates habitat that other species can use.”

Facebook Twitter Pinterest European beavers were reintroduced at Ham Fen nature reserve in Kent, UK. Photograph: Terry Whittaker/Alamy

An unlicensed population of around 150 beavers has also established itself on the river Tay, near Dundee. The Scottish government initially planned to trap them, but later decided against it. Next year, Holyrood is expected to make a decision on what to do about both sets of beavers. Knapdale also serves as an example that reintroductions rarely happen overnight. It took 11 years to become reality, after the trial was first floated in 1998. Campaigners have been lobbying for a similar amount of time to return the herbivores to England and Wales, but plans to bring them back in the wild in Ceredigion in Wales this year have not yet come to fruition. In England, slow progress appears to have prompted individuals to take matters into their own hands.

This February, Tom Buckley, a retired environmental scientist, photographed beavers on the river Otter in Devon, the first in the wild in England for centuries. Local people attending a public meeting this August at Ottery St Mary, a village along the river, say that the beavers have been out in the area for several years longer, a secret known to some but until recently not broadcast more widely, though it remains a mystery where they came from.

The Department for the Environment, Food and Rural Affairs said this summer that it would trap the beavers, in part to test for a disease not currently in the UK (alveolar echinococcosis), but officials will not say whether the family, which expanded with the addition of three kits in July, will be allowed to return or will be rehoused elsewhere at a zoo or other site, even if they test all-clear for the disease. People living near the river Otter are certainly largely in favour of the beavers being returned, a straw poll by the Observer suggests. Adrian Forster, who lives a few hundred yards from the river and wrote a song about the beavers, said: “I do feel really passionately that we have removed them by killing them centuries ago, and just as a matter of fairness and justice, if we can do anything to return them to their native habitat we ought to do that. They were a native species, and unless we have very good reasons, however they’ve managed to get there, they ought to be left alone.”

Local resident Pam Baker-Clare said: “Everyone seemed very proud of the beavers. But if the government gets mixed up in this, they will disappear.”

Some visitors to the meeting, organised by the Devon Wildlife Trust, which is looking to submit a bid for a licence for the beavers to return, sounded more wary.

“I’m a bit cautious about the future. I appreciate that reintroducing beavers means we don’t have any predators other than man, because the wolf has disappeared so obviously the population increase [of beavers] and what happens in a 100 years’ time has to be answered,” said John Killingbeck, who lives nearby. “Our landscape has changed since we had beavers. We are much more densely populated, we are trying to farm, there are effects on rivers, on catchment zones, on fisheries.”

About an hour away near Okehampton in north Devon, a three-hectare fenced enclosure demonstrates dramatically why beavers are referred to as a keystone species.

Hundreds of fallen willow and birch trunks criss-cross the captive trial site, with distinctive pencil-shaped stubs remaining amid a network of canals, paths, small dams and 10 ponds that a pair of beavers introduced in 2011 have built, along with an increasingly elaborate lodge where they sleep during the day before emerging at night to work.

“The impact they’ve had has been phenomenal, they’ve blown us away, they’ve done what we hoped for and more. We’ve been surprised at how effective they’ve been,” says Mark Elliott of the Devon Wildlife Trust, which runs the project.

There was no static water here before, and just 10 clumps of frogspawn were counted in 2010. This year, 370 clumps were spotted. Around the ponds, butterflies dance and dragonflies hover.

Drawn by the invertebrates that have appeared as the forest cover has thinned out, birds have arrived, including herons feasting on the frogs, spotted flycatchers, snipe and woodcock. Vegetation has sprouted up in the gaps created by the felled trees, including orchids, pond weeds and purple moor grass, a “really good sign” of the habitat’s health, Elliott says.

The University of Exeter is now measuring the height of water levels and collecting water samples to see whether, as expected, the habitat the beavers create filters and cleans the water, removing phosphates and other pollutants. The project could also generate data that proves beavers can reduce flood risk – during this winter’s floods there were calls by the Mammal Society to reintroduce them for just that purpose.

“If we can provide evidence that beavers in the top of the catchments reduce floods downstream, that’s gold dust really,” Elliott said. “If you can reduce the flood risk downstream by 10%, that could in many cases be the difference between flooding and not flooding. It can mean the size of your flood defences can be lower. It means the cost of that sort of work can be reduced. Potentially it’s of huge financial benefit to society.”

Yet both the farming and angling lobbies in the UK are opposed to beavers returning to the wild. The National Farmers’ Union’s countryside adviser, Claire Robinson, said: “We believe efforts, and finances, would be better focused on retaining current biodiversity.” If beavers were allowed out in the wild, there would “rightly be concerns about them causing damage to the environment, including farmland”, she said.

Mark Owen, head of freshwater at the Angling Trust, said the landscape had changed so much since beavers were last in Britain that it would be inappropriate to bring them back. “In the last 500 years-odd, we’ve heavily straightened our rivers, we’ve caused pollution, so when beavers were in this country, the river system would’ve looked completely different. Rather than a top-down approach of introducing a water engineer like a beaver, we’d rather rivers were improved to a point where we could look at reintroducing beavers.” Owen cited a list of concerns, including half-gnawed trees posing a threat to fishermen and the potential dangers posed when beaver dams break.

Even among the most enthusiastic rewilding supporters, however, few believe that reintroduced species should be allowed to run truly wild. None, even Monbiot, are arguing for a blanket, mass return of farmland to nature. But advocates hope that even on this crowded island, there is still room for more wildlife, and that people could learn to live alongside it.

Elliot, walking alongside a beaver canal, says: “If we do get beavers back [in the wild], we have to accept we will have to manage conflicts, like they do in Europe. There’s no point in reintroducing an animal and not managing conflict.”