France's experimental fusion reactor would work like the sun

The world's most ambitious attempt to harness fusion as a source of power is taking shape in the south of France.

Fusion is the process that drives the sun - atoms are forced together to release energy - and repeating it here on Earth could in theory offer an almost endless supply of electricity.

The construction of a vast experimental reactor has now entered a key phase.

Science editor David Shukman was given special access to explain how the reactor would work.