When electricity from nuclear fusion arrives (not to be confused with fission) it will change the world out of all recognition. At present the civilised world runs mainly on oil – and the handful of biggest oil producers has a disproportionate say in world affairs. Besides which, the burning of oil is wrecking the climate.

Working fusion reactors actually exist – and the biggest one (of the tokamak type): the JT-60SA in Japan, has just become operational. Another tokamak under construction: the EU’s International Thermonuclear Experimental Reactor (ITER) will dwarf the JT-60SA. But ITER is seriously overdue and over-budget, and won’t be powering our homes and industry anytime soon.

The snag with all present-day tokamaks is that the amount of energy they yield is scarcely more than the amount they need to start the reaction and sustain it. Clearly none of them are a going concern until this problem is addressed. The present generation of experimental tokamaks are being built precisely to overcome it.

Let’s not forget that the Earth already gets most of its energy from a vast natural fusion reactor in the sky. It’s called the Sun.