My god, the BFI are fantastic. This interactive presentation, starring the excellent Derek Jacobi, explains the development of the GPO Film Unit. The GPO (General Post Office) regulated the early development of the communications industry in Britain, with BT (British Telecommunications), and the Royal Mail being the direct descendants. The most famous example of the GPO Film Unit’s work is Night Mail (1936), which presents the complex distribution of mail by train, and features a poem by WH Auden, the opening lines of which (“This is the Night Mail crossing the border / Bringing the cheque and the postal order”) was used in a 1980’s British Rail advert.