Mr Cleaver was a Welsh nuclear adviser, charged by the British government with investigating the Blaidd Drwg Power Station Project. He realised that the power station was badly designed, fearing that the suppression pool would cause the hydrogen recombiners to fail. Thus the containment isolation system would collapse, resulting in a meltdown - a potential nuclear explosion which would take most of South Wales with it.
After posting some of his fears on the Internet, though not showing it to anyone directly, he reported his findings to the Mayor of Cardiff, former MI5 operative Margaret Blaine. She claimed she would stop the catastrophe. As Mr Cleaver turned around, feeling relieved, Margaret, who was actually Blon Fel-Fotch Passameer-Day Slitheen decapitated him. She covered up his death by saying that he slipped on a very icy patch. (TV: Boom Town)