The UK's newest fusion reactor, ST40, was switched on last week, and has already managed to achieve 'first plasma' - successfully generating a scorching blob of electrically-charged gas (or plasma) within its core.

The aim is for the tokamak reactor to heat plasma up to 100 million degrees Celsius (180 million degrees Fahrenheit) by 2018 - seven times hotter than the centre of the Sun. That's the 'fusion' threshold, at which hydrogen atoms can begin to fuse into helium, unleashing limitless, clean energy in the process.

"Today is an important day for fusion energy development in the UK, and the world," said David Kingham, CEO of Tokamak Energy, the company behind ST40.

"We are unveiling the first world-class controlled fusion device to have been designed, built and operated by a private venture. The ST40 is a machine that will show fusion temperatures - 100 million degrees - are possible in compact, cost-effective reactors. This will allow fusion power to be achieved in years, not decades."