Egon Bretscher was a Swiss-born British chemist and nuclear physicist and Head of the Nuclear Physics Division from 1948 to 1966 at the Atomic Energy Research Establishment, also known as Harwell Laboratory, in Harwell, United Kingdom. He was one of the pioneers in nuclear fission research and one of the first to foresee that plutonium could be used as an energy source. His work on nuclear physics led to his involvement in the British atomic bomb research project Tube Alloys and his membership of the British Mission to the Manhattan Project at Los Alamos, where he worked in Enrico Fermi's Advanced Development Division in the F-3 Super Experimentation group. His contributions up to 1945 are discussed by Margaret Gowing in her "Britain and Atomic Energy, 1935-1945."

The Atomic Energy Research Establishment (AERE) was the main centre for atomic energy research and development in the United Kingdom from 1946 to the 1990s. It was created, owned and funded by the British Government.