Oh dear, here we go again. The escape of beavers from a colony in Devon mirrors past experiences with animals introduced to this country from abroad, then allowed to spread, often with dire consequences.

The coypu, a beaver-like creature brought from South America for fur farming in the 1920s, became such a menace in East Anglia that it took a ten-year campaign to get rid of it.

Mink, one of nature’s most efficient killers, which escaped from captivity in 1929, are now endemic in the British mainland, a threat to poultry and small animals. The grey squirrel, which was imported from the US, is having to be culled in the Highlands to prevent it from eliminating the native red squirrel.

Despite this history, the beaver is now part of an official programme to reintroduce them to Britain after an absence of 500 years. A batch of 17 has been imported from Norway and is being held in quarantine in Devon before being released into the wild in Knapdale, Argyll, on the West Coast of Scotland. Scottish Natural Heritage hopes that, if the scheme proves successful, these animals will again be a common sight in the countryside.

Not everyone is happy. Indeed, no one involved in nurturing salmon or sea trout rivers – a staple industry in the West of Scotland - is happy. They point out that what beavers do is build dams; that dams block rivers; and that a blocked river prevents salmon from breeding. Why, they ask, would you introduce a species whose spread would threaten a basic natural resource?

The experience in other countries is not promising. In Latvia, Lithuania and Estonia, they are having to cull the beaver, because the population has grown to more than 200,000 – which just happens to be point at which the coypu ceased being lovable furry creatures and were designated a menace.

Conservationists respond that the latest trial will be carefully controlled, and that no beaver will be allowed to escape from Knapdale until the outcome is properly assessed. To which the answer is: pull the other one.

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