In the first of Elementary Business - a new series of programmes about the chemical elements - Justin Rowlatt asks whether phosphorus poses the biggest looming crisis that you have never heard of. Since 1945, the world's population has tripled. Yet the fact that we've still managed to feed all those mouths is in no small part thanks to phosphates. We mine them, turn them into fertiliser, and then spread them onto our fields, whence they are ultimately washed away into the ocean. Justin speaks to chemist Andrea Sella to find out just why phosphorus is so vital to sustaining life, and modern agriculture. He also hears from Jeremy Grantham, a voice from the world of high finance, who warns that pretty soon Morocco may find itself with the dubious honour of a near-monopoly of the world's remaining phosphate supplies. And Justin travels to the lowly town of Slough, near London, to take a look at one new way of staving off the dreaded day when the world eventually runs out of the stuff.

(Photo: The Thames Valley sewage treatment facility at Slough, which can extract phosphorus)