Did you know that we have rainforest, lush, green rainforest, right here in the UK? Many don't, yet it's once of our most ancient - and threatened - habitats. Gnarled trees, twisted with age, covered from root to tip in mosses and lichens, epiphytic ferns dripping from every branch.

Once existing in a vast swathe right down the west coast of Britain, "temperate rainforest" is one of the world's rarest habitats. There are species living here that can live nowhere else, but it's been gradually encroached on by humans for centuries. Now clinging on in small pockets, you can find patches of rainforest if you know where to look: in places like Dartmoor, West Wales and the west coast of Scotland. But there may be other patches out there - quietly enduring the passing centuries.

Helen Mark takes a walk into the secret forests of Britain to find out how we can save them. In Wales, projects are underway to save and expand the Celtic Rainforests, rescuing them from invading rhododendrons, and employing some hardy (but elusive) Highland Cattle to help keep the weeds in check. And a new project is launched this year, aiming to find and map the full extend of the British rainforest for the first time. They need your help to track down every last bit of it.

Presented by Helen Mark