In a month of continuing controversy about the aims and methods of the ' documentary', Arena presents a classic film by one of the pioneers of the movement-Humphrey Jennings 's Listen to Britain. Made in 1941, it will be seen here, complete, for the first time on British television. Also Gavin Millar looks at the craft of recent documentary makers, focusing on the techniques of the BBC's current Police series. With Roger Graef , Charles Stewart and the team who made it.