Slough sewage works
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Phosphorus: Flushing away our future?

Justin Rowlatt 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 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.