Helen Mark visits 50 square miles that were neither England nor Scotland. The Debatable Lands, between Carlisle and Gretna, were home to untameable crime families that petrified the most powerful of Lords and Kings. For hundreds of years governments in London and Edinburgh left the region to its own laws and moral codes. When they did intervene, the result was an explosion of violence that's still visible in the landscape of derelict towers and still audible in the Border Ballads collected by Walter Scott.

Author, Graham Robb guides Helen through the region's complex history and Ian Scott Martin takes her to the ramparts of Gilnockie Tower- the fearsome stronghold of the Armstrong family, one of the most notorious clans of Border Reivers.

The Union of the Crowns in the early 17th century brought the age of the Debatable Land to an end, ushering in a long period of peace broken abruptly in 1915. On the Western Front the British Army was running out of shells. In Westminster the government fell and the decision was made to build an enormous 9 mile long munitions factory, stretching across the region. Rebecca Short of the Devil's Porridge Museum guides Helen around the remains of the industrial landscape in which 30,000 people- 16,000 of them women- worked in the production of the cordite that propelled shells across the battlefields of Belgium and France.

The western tip of the Debatable Land reaches out to the saltmarshes of the Solway Firth. This apparently peaceful landscape soon yields its secrets. The land is constantly battered and transformed by the tides while animals and plants have to adapt to survive the harsh and dynamic conditions. Helen explores the creeks, bogs and rivers with David Pickett of the Wildfowl and Wetlands Trust and Chris Miles of the Botanical Society of Britain and Ireland.

Producer: Alasdair Cross