Tom Heap looks at whether we're running out of phosphorus. It's an essential element in fertiliser and all life on earth depends on it. Nowadays we get it from mining phosphate rock, which is a finite resource. Some scientists have predicted that we could run out within decades.

Britain has no phosphate rock reserves of its own, and with 80 per cent of known rock under the control of one country, Morocco, should we be taking future supplies more seriously, as a matter of national security?

Tom investigates whether there are alternatives to phosphate rock, such as extracting phosphorus from sewage. He learns about a nineteenth century gold rush in East Anglia, where fortunes were made from extracting phosphate from fossilised dinosaur bones and droppings. In an emergency, could we go back to this old method?

Producer: Jolyon Jenkins.