Incidentally, the UK law (of 1946) defines atomic energy as;
“atomic energy” means the energy released from atomic nuclei as the result of any process, including the fission process, but does not include energy released in any process of natural transmutation or radioactive decay which is not accelerated or influenced by external means”
whereas in the US it is
The term "atomic energy" means all forms of energy released in the course of nuclear fissionor nuclear transformation.
The thing with the UK definition is that in fusion you make an unstable nucleus that then decays by a natural process. The act of fusing nucleii cannot accelarate the fused nucleus, because it did not exist prior to the act of the fusion. So the UK law doesn't appear to include fusion within its definition, whereas the US law does so a little more convincingly.