Turning ten centuries of history on its head, Dan Cruickshank brings Britain's defence heritage to life in the first of three programmes. Secret tunnels, watchtowers, castles, forts and gun emplacements are among his destinations, as he recreates some of the most explosive moments since the Norman Conquest.

A French invasion loomed in 1804. How did Britain respond to the threat of Napoleon's army? Dan Cruickshank continues his exploration into the heritage of Britain's defences in the second of the series.

An insight into how Britain, under the threat of German invasion in the Second World War, reinvented itself as a fortified encampment, and how with the Channel no longer a barrier affording any protection, the country turned its attention to the skies. Cruickshank visits Farnborough to see stages in the development of radar, and recalls how Dover witnessed the installation of two huge guns that came to symbolise the defence of Britain.