Using guidance from a team of experts, a magical underground world was recreated in the West Country. It includes a vast cross-section of a rabbit warren; a water vole burrow with its own riverbank; and a full size badger sett. The film-makers then used the latest in filming technology to shed light on this previously secret dark world.

The unique project based at two locations in Devon and Somerset reveals new science and TV firsts. It explains how the animals create their burrows, how they organise themselves underground and how they find mates and give birth.

Beginning in winter, the cameras follow the dominant female rabbit Hazel who sets herself up in the best chamber in the warren. Thumper is the dominant male and never far from her side. Much to Chris and the experts’ delight, the other rabbits, who are from a local rescue centre, all soon settle into the replica warren.