It's worth remembering the other people involved in this. Peierls and Frisch worked under Oliphant at the University of Birmingham, and they wrote the memorandu

It's worth remembering the other people involved in this. Peierls and Frisch worked under Oliphant at the University of Birmingham, and they wrote the memorandum which formed a major part of the Tizard Mission to the US. This also included the much better design for the Cavity Magnetron, also developed in Birmingham by Randall and Boot, who also worked for Oliphant. In 1943 a British delegation led by James Chadwick (who discovered the neutron and won the 1935 Nobel Prize) went to work on the Manhattan Project, and included Oliphant, Peierls and Frisch, as well as Klaus Fuchs (who it turned out was a Soviet spy) and Tony Skyrme (more famous for his work on what later became known as 'skyrmions'), all from Birmingham, the Danish Physicist Neils Bohr (Nobel Prize winner in 1922) and Lord Cherwell who had invited Bohr to England and who was an advisor to Churchill and who advocated area bombings of Germany. The British techological 'Tube Alloys' programme was absorbed into the Manhattan project. Bohr advocated sharing the technological developments with the Russians, and met both Churchill and Roosevelt in attempts to try and convince them of this. The British mission basically left with the passing of the Atomic Energy Act 1946 which prohibited the sharing of nuclear secrets with allies by the US government. It wasn't until a few years after the British developed their own nuclear warheads (the first being the Blue Danube) that cooperation on nuclear warhead technology began again in 1958.