There are beasts out there, lurking in the countryside.
Wild boars are now well-established in the woods of southern England, having escaped from farms. Big cats like lynx and puma, after appearing from who-knows-where, seem to melt into the landscape; seldom seen, apart from the odd footprint or a sudden blare of eyes in the headlights. There are also beavers. They are seldom reported – and not often seen – but they are there.
The toothy creatures have been living quietly along the river Tay in central Scotland for at least 10 years. They are thought to be the progeny of a pair that escaped from a wildlife park.
Officially there are between seven and 20, but there may be as many as 50. They have certainly bred in the wild. But they tend to keep out of sight, even though signs of beaver activity have been spotted along the catchment of the river all the way from Loch Tummel in the Highlands to Tentsmuir on the coast: proof that Scotland in general and Tayside in particular offers some "optimal beaver habitat".
You might think naturalists would be jumping for joy. But they are not, or at least not at Scottish Natural Heritage (SNH), the body that looks after all things natural north of the border.
The trouble is that these beavers are not part of an official reintroduction project. Under the rules, says SNH, the only acceptable introduction is one sanctioned by Government.
Leaving these animals in the wild, it says, "would mean choosing to ignore well-established wildlife legislation... not something SNH, or any other Government organisation, can do".
Although there is no record of them causing significant damage, SNH has decided to stop what it sees as a potential problem in its tracks: the errant beavers must go and are being tracked, trapped and sent to the zoo.
"There are strict international guidelines covering the reintroduction of species," points out an SNH spokesman. "They have not been applied in the release of these beavers." The blame, it insists, lies with those who allowed the animals to escape in the first place: "Had the keepers of these animals fulfilled their responsibility and prevented their escape, we would not be in this position."
Rounding them up has now become "a matter of urgency".
SNH comes close to asserting that its plan is in the animals' best interests. Since they are not within the scope of protective legislation, the Tayside beavers could be shot by any landowner with a grievance (although no one seems to have done so). It is better for them that they should be cared for by professionally-qualified keepers.
SNH and its partners have invested much time and effort into the official campaign to re-establish European Beavers in Scotland. But since the release of the beaver is a controversial issue, they are proceeding with due caution.
The trial site is Knapdale in the western Highlands: a wooded area owned by the Forestry Commission and chosen for its remoteness from farmland.
Even so, the initial application was turned down and it took years of delay before the Scottish Executive granted the licence to release three families of beavers there in 2009.
SNH's determination to round up the Tayside "interlopers" has alarmed and puzzled the wild beaver lobby both in Scotland and Europe. Campaigners have even set up a Facebook page "to save the wild beavers of the Tay".
The matter has been reported widely in the Scottish media, but hardly at all in England. Yet the introduction of beavers and other once-native wild animals concerns us all. One day the beaver will almost certainly be returned to the wild in England, too.
Derek Gow, who looked after the Knapdale beavers while they were in quarantine, considers the SNH's plan "ill-considered and profoundly wrong".
You can forget about animal welfare for a start, he says: "The random removal of adult beavers by trapping in winter could result in the death of one-year-olds from starvation or hypothermia." SNH insists it has taken the best advice and any youngsters are now old enough to survive without their mother.
However, the fate of the trapped beavers is in doubt. There are no zoological facilities in Britain or Europe with the capacity to keep them all, says Mr Gow, and suitable habitat is already effectively full-up: "If there is no space in captivity and no prospect of their release elsewhere, then they will have to be killed by rifle shots or lethal injections. It is inconceivable that SNH, the Scottish Executive and their partners are not perfectly aware of this."
Mr Gow also questions whether SNH, for all its assertions about strict legality, is in fact acting within the letter of the law. An official study undertaken by Natural England indicates that, once they are established in the wild and within part of their former natural range, the beavers are within the protection of EU law. The legal argument revolves around whether the beaver could be said to be "resident" in the UK, even though "resident" has never been defined legally.
The Scottish Rural Property and Business Association (SRPBA, formerly the Scottish Landowners Association) is adamant that the beaver is in no sense a Scottish resident, since the landscape has, it contends, changed out of recognition since the animal died out 400 years ago.
Paul Ramsay, who maintains a captive beaver colony in the Scottish lowlands, believes that SNH has acted under pressure. The SRPBA's newsletter congratulates itself that the body had heeded their advice, which it characterises as "a victory".
Many Scottish landowners are not at all keen on the idea of wild beavers roaming the landscape.
The Tweed Foundation, for example, has spoken darkly about the animals interfering with the course of migrating salmon although, says Ramsay, there is not a shred of evidence for this.
The beaver lobby has another argument for sparing the Tayside residents. The Tay, says Sir John Lister-Kaye – who keeps a small colony at his field study centre near Inverness – offers possibly the best beaver habitat in Scotland, if not in the UK. The irony, he says, is that "if the Knapdale trial is a success, the most likely place for a reintroduction will be the Tay system". Knapdale, by its very isolation, is of limited value as a testing ground. It will not be able to answer the critics' contentions about damage to game fisheries or farm crops. In Tayside, says Sir John, "the banks are farmed to the edge, while the Tay is one of Scotland's premier salmon rivers".
It would afford much better opportunities for study and potential harmonisation with landowners. How will it look if the SNH removes the beavers – at public expense – only to reintroduce them again (also at public expense) in a few years' time?
"We are not in outright opposition to SNH," insists Sir John Lister-Kaye. "We simply want them to reconsider their decision. We want the Tayside beavers to be treated as a monitoring project rather than as a removal." He adds he would have no objection to trapping and removing any animals that had become a problem. This is standard practice in Europe and it seems to work.
The SNH may be on a sticky wicket. There was majority support from the Scots public for the reintroduction of beavers. They are animals of unusual appeal; proverbially busy beasts; always eagerly at work, chewing trees and building dams. They improve their habitat by digging and constructing twiggy dams and lodges and, in the process, create better habitat for many other species of wildlife. They could also become a significant tourist attraction.
The beaver lobby is not going to let this go without a fight. So far the debate has been fairly restrained, but it has the makings of a first-class row.
To the Scottish establishment it might make sense to pour money and resources into one set of beavers, while wiping out the other. To others it could look more like a particularly surreal episode of Yes Minister.
Tails of the river bank: Beaver facts and figures
*Beavers are the world's second-largest rodent, measuring about a metre from nose to tail and weighing up to 30 kilograms.
*There are two species, the European Beaver, Castor fiber, and the closely related Canadian Beaver, Castor canadensis.
*The beaver was once widespread in Britain but died out by the 17th century, probably from over-zealous hunting. Once listed as endangered and reduced to only 400 individuals, it has recently been reintroduced across its former range.
*Beavers mate for life and live in family groups. Young beavers, born in May and June, are called kits.
*Wild beavers usually live for eight to 10 years, though captive animals have lived up to 25 years.
*Beavers eat only plants, including grasses, twigs and bark. Favourite trees are willow, aspen and poplar. They do not eat fish.
*Beavers were hunted almost to extinction for castoreum, an aspirin-like substance found in special glands and the male beaver's testicles. Their fur was also in demand for hats.
*Beavers have been reintroduced in 24 European countries, including France and Bosnia
*Beaver reintroduction in Sweden began with 80 animals between 1922 and 1939
*In 1997 beavers were released in Romania after they had been extinct there for 200 yearsReuse content