Is the dream of nuclear fusion dead? Why the international experimental reactor is in ‘big trouble’

The 35-nation Iter project has a groundbreaking aim to create clean and limitless energy but it is turning into the most delayed and cost-inflated science project in history'

It was a project that promised the sun. Researchers would use the world's most advanced technology to design a machine that could generate atomic fusion, the process that drives the stars - and so create a source of cheap, non-polluting power.

That was initially the aim of the International Thermonuclear Experimental Reactor (Iter) which 35 countries - including European states, China, Russia and the US - agreed to build at Saint-Paul-lez-Durance in southern France at a starting cost of $6bn. Work began in 2010, with a commitment that there would be energy-producing reactions by 2020.