Winston Churchill, wartime Prime Minister of Great Britain and its empire during the Second World War, is one of the most recognisable figures of world history. The man dominated Whitehall and Westminster, but many of his most vital decisions during the war years were taken away from the public eye. Not in Parliament, nor in Downing Street. But underground - in the Cabinet War Rooms. To this day, they are beautifully preserved, famously portrayed in the recent award winning film 'Darkest Hour.' Dan Snow pays a visit to the Churchill War Rooms, walking in the footsteps of the great man and his many associates during the Second World War.