Throughout our history on these islands, we have created places for our own use, without giving a second thought for wildlife. But the wildlife has not only found a way to survive, but has thrived in these unexpected places. In the last of the series, join Alan Titchmarsh on a journey around Secret Britain, to find the birds that moved in when the Iron Age settlers moved out, the plant that hitched a ride on the railways, and the oldest and toughest organism of the lot – lichens. At a time when we are rediscovering our relationship with nature, these secret places show us just how tough and resilient the natural world can be.