The GPO Film Unit - 50 years old this year - went where no Hollywood film studio would dare to go in 1933. Down the mines, across the Alps, through the storms of the North Sea... they really were a dedicated and intrepid group of filmmakers. Held together by a dour and dynamic Scot, John Gnerson - the man who first coined the word "documentary" - they made some of the greatest factual films of the 1930s, which still provide a fascinating insight into the everyday life of the time. Tonight, Arena tells the story of this remarkable period of British cinema.