Leon graduated from London in 1940 and began work on an M.Sc. However the war meant that students from King's College were sent to Bristol University and it was there that he completed his Master's degree.
Leon nagtapos mula sa London sa 1940 at nagsimulang magtrabaho sa isang M.Sc. Subalit ang digmaan sinadya na mag-aaral mula sa King's College ay ipinadala sa Bristol University at ito ay doon na niya natapos ang kanyang Master's degree.