The medicinal leech is one of nature’s least loved hunters. Armed with three strong interlocking jaws and with a taste for blood, they will swim hungrily towards humans, deer or cattle that wander into their ponds to bathe, fish or drink.

Yet this small predator is the focus of an unlikely reintroduction programme by conservationists working in a small laboratory deep in the Scottish Highlands, at a wildlife park best known for its polar bears, wildcats and wolves.

They want to see hundreds released into Scottish lochs and streams, in the first project to repopulate the countryside with leeches after hundreds of years of habitat loss and exploitation.