The physicist Brian Flowers, who has died at the age of 85, was the outstanding scientific and academic administrator of his generation, his career culminating in 12 years as rector of Imperial College London until 1985, and then five years as vice-chancellor of London University. However, he contributed much more outside even the very broad fields of science and the universities, chairing public bodies and as a member of the House of Lords, which he joined in 1979 as Baron Flowers.

Everything he did was characterised by imagination and by his determination to find the right – rather than the easy and the easily acceptable – solution. He believed that although one major purpose of science is the betterment of mankind, another is the proper management of the earth’s resources.

His commitment to bettering the human condition came naturally from the son of a noted Welsh preacher, the Rev Harold Flowers, and his wife Marian. Born in Blackburn, Lancashire, Brian went to Bishop Gore grammar school, Swansea, where an extraordinarily gifted teacher, a Mr Foukes, encouraged the first signs of his passionate interest in physics. At Gonville and Caius College, Cambridge, he studied physics with electronics, gaining his wartime degree in two years with such obvious brilliance that in 1944, before he was 20, he was recruited by the British nuclear physics pioneer John Cockcroft to the Anglo-Canadian atomic bomb project at Chalk River, Ontario.

In 1946, Cockcroft brought Flowers back to Britain to work in Otto Frisch’s group in the nuclear physics division of the Atomic Energy Research Establishment (AERE) at Harwell, Oxfordshire. It was there that Flowers met Mary Behrens, from a well-known Manchester Liberal family and later to become his wife. At the time she was married to Oscar Buneman, a member of the theoretical physics group under Klaus Fuchs.

In the nuclear division under Frisch, Flowers found life somewhat disorientated, and he transferred to Fuchs’s theoretical group. However, in 1950 Fuchs was arrested as a Soviet agent. Flowers went to Birmingham University to work under Rudolf Peierls. With hindsight, and leaving aside the creative work he did on spectroscopy at Birmingham, it seems that Flowers was already being groomed to take the place of the brilliant but disgraced Fuchs, who was convicted, imprisoned and in 1959 left for East Germany.

In 1951, Flowers married Mary. A year later he returned to Harwell as the new head of theoretical physics, a certain springboard for the career that followed.

Apart from his contribution to the atomic energy project, Flowers had already begun to establish himself as a nuclear structure physicist of international standing: in 1958 he was appointed professor of theoretical physics at Manchester University, and three years later elected a fellow of the Royal Society. In 1967, he was seconded to be the chairman of the Science Research Council. His great contribution there was to overcome the differences between the very disparate bodies from which it had recently been formed, and to forge powerful links with university science and engineering departments. (He would return to Manchester as the university’s chancellor from 1994-2001.)

The SRC and its companion research councils had been established by the government in response to a report by the secretary to the cabinet, Sir Burke Trend, on the organisation of civil science, emphasising the desirability of strong working relationships between the universities and government laboratories. With the outstanding success of an academic in this post, an important principle was established, though it meant forgoing the contribution Flowers would undoubtedly have continued to make to physics.

When the rectorship of Imperial College, then part of London University, became vacant in 1973, he was the obvious person to appoint, just as he was later as vice-chancellor.

Not only was he president of the Institute of Physics and of the European Science Foundation, he was also president of the National Society for Clean Air. He must have been the only governor of the Weizmann Science Institute, in Israel, who had been also a visiting professor at Cairo University. He received many international accolades, including being made Officier de la Légion d’Honneur (1981).

In 1969 he was knighted, and four years later became chairman of the Royal Commission on Environmental Pollution. Its controversial sixth report, Nuclear Energy and the Environment (1976), pointed to the undesirability of committing to a large-scale programme of nuclear power until a method had been found for dealing with radioactive waste.

In the Lords, he was a founder member, in 1981, of the Social Democratic party, and a member of its select committee on science and technology most of the time from 1982 to 2002. As a result, he directly influenced several inquiries, including that on priorities in medical research, which led to the NHS appointment of a director of research and development and the concept of a knowledge-based service. He was deeply involved in the report on research and development in nuclear power, and a visionary report on essential priorities for the science base.

Under his chairmanship (1989-93), the select committee played an important role in the creation of the Office of Science and Technology in 1992, and the science white paper of 1993.

It was typical that Flowers should call on the Palace of Westminster to take a very long view of science, development and the human condition, an approach which he also expressed as president of the Parliamentary and Scientific Committee (1993-97). With great skill, Flowers sought, and brought, balance to the highest levels of scientific administration and debate. He somehow managed to be tough yet approachable, to see the present in terms of the future, and was always interested in ideas that reached across the spectrum of human activities and achievements.

If, at times, he was troubled by the uncertainties of global security – he supported the Pugwash conferences on science and world affairs – it was because he detested profligacy, because his timescale stood astride the expediencies of national and world politics, and because he was among the most perceptive and gentle of the nuclear pioneers. He was, in short, a true giant of his time.

His contributions to the way that society may work better with the help of science were born of deep humanitarian convictions and a broad culture. We are unlikely to see another “science politician” who is an accomplished cellist and painter in oils.

His marriage to Mary brought him two stepsons, Peter and Michael Buneman; they all survive him.

Bill Gelletly writes: The theoretical physics division at Harwell in the early 1950s under Flowers was a very lively place, with a galaxy of talent including Tony Skyrme, Phil Elliott, Tony Lane and John Soper. One of Flowers’s major achievements was to ensure that the theorists interacted closely with experimenters working on the same problems at Harwell and Oxford.

This group came together at an auspicious time. It was known that atomic nuclei were complex objects made up of neutrons and protons and that they could be described only by quantum mechanics. The best information on the forces between these nucleons, as they are known, was empirical. As we still do not have any means of determining this force from first principles, we depend on models of nuclei.

In the early 1950s, two competing and apparently contradictory models held sway. The shell model asserted that the nucleons were arranged in orbits round the nucleus just like the electrons in the atom. Quantum mechanical considerations ensured that they filled the orbits two at a time, allowing the explanation of many regularities observed in nuclear properties based on the idea that when a set of orbits is filled, it completes a “shell”, and the system is then more tightly bound together. The collective model, on the other hand, involved the motion of many nucleons and could explain the observed spectra which exhibited all the characteristics of a rotating or vibrating system.

Flowers developed the algebra to describe the various nuclear shells. In a series of papers, with Elliott in particular, he showed that both models could describe what was observed. This work had essentially unified the collective and shell models. It was to lead Elliott to the application of group theory to nuclear properties. We can still see these strands of the work initiated by Flowers and his colleagues in current research.

We have moved away from the idea of a fixed shell structure in all nuclei, with profound consequences, for example, for our understanding of how the chemical elements are generated in stars and hence their relative abundances. Nevertheless, the basic ideas embodied in the work of Flowers and his colleagues underpin the much more complex shell model calculations made possible by the enormous advances in computing techniques in the last half century.

• Brian Hilton Flowers, Baron Flowers, physicist, administrator, politician and public servant, born 13 September 1924; died 25 June 2010