In 1953, Butler left Manchester to lead a high-energy nuclear physics group at Imperial College in London. He was promoted to professor in 1957, and head of the physics department in 1963. While at Imperial College London, Butler chaired the consortium established to design the British National Hydrogen Bubble Chamber, which was operated at the Rutherford Appleton Laboratory and CERN. From 1964, he chaired the CERN Track Chamber Committee. He was elected a fellow of the Royal Society in 1961, and served as dean of the Royal College of Science between 1966 and 1969. Over this period he became increasingly interested in educational policy, joining the academic planning board of the University of Kent in 1963, the Schools Council in 1965, and the University Grants Committee in 1966. He eventually served on the Schools Council for 19 years.