Nuclear fusion promises an unlimited supply of clean energy, but will it always be just that; a promise? 

Scientists at the Spherical Tokamak for Energy Production (STEP) project in the UK hope not. They're developing a prototype plant designed to be operating by 2040. But as Neil Cairns finds, there are still major engineering and physics challenges to overcome. 

He travels to the UK Atomic Energy Authority's Culham Campus near Oxford to see the latest fusion experiments being run on a smaller spherical Tokamak and visits the robotics lab to see how they are developing robots that will help operate the fusion power plant of the future.

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