The few specialist graduates who choose teaching are being enticed into private schools by the promise of better facilities and the freedom to teach their own subject, say academics from the University of Liverpool.
The study, one of two independent analyses commissioned by the National Union of Teachers, reveals a more deep-seated teacher-recruitment problem than the Government has so far admitted, warned Doug McAvoy, the union's general secretary.
Teaching is increasingly dominated by the over-40s and the number of men has plummeted, an analysis by researchers at Ruskin College, Oxford, showed.
Mr McAvoy said poor pay and conditions were driving graduates away. He said: "This is a frightening picture: an ageing profession attracting too few would-be teachers and too few highly-qualified graduates."
The Liverpool research showed physicists are attracted to independent schools where physics, chemistry and biology are more often taught separately rather than to state schools which teach combined science.
Dr Pamela Robinson, who carried out the analysis with Professor Alan Smithers, said the physical sciences were caught in a vicious circle of dwindling popularity. She said: "Too few pupils attracted to the physical sciences at school restricts the pool of graduates from which the teachers can be drawn to make the physical sciences attractive to pupils."
Only 12 per cent of last year's trainee science teachers had a physics degree - 277 students - while just 17 per cent were chemistry graduates. In 1983 science trainees were equally split between the three sciences.