A shortage of clinical academics is threatening the ability of medical schools to provide the big expansion in the number of junior doctors promised for the NHS.

The British Medical Association (BMA) yesterday warned that medical schools were struggling to cope with rising student numbers because of 322 vacant posts for lecturers and 79 for professors.

The recruitment situation is undermining the quality of teaching for undergraduates, the BMA's annual conference for clinical academics in London was told. Serious doubts were also raised over whether Labour's promise to "guarantee a decade of unprecedented expansion in doctor numbers in the NHS" could be met.

At least 11 per cent of hospital consultants used to couple their clinical work with a teaching role, but that proportion has fallen to just 8 per cent, or less than 1,000 clinical academics who work in the NHS.

Colin Smith, chairman of the BMA's medical academics' committee, said the staff shortages were causing concern over standards of teaching.

"We are responsible to the General Medical Council for the quality of graduates. We have to ensure they have the right clinical skills and the right ethical approach. This is not a job to be skimped, yet 60 per cent of our time is spent on direct patient care. Medical teaching needs a higher profile and we need enough experienced senior doctors to enthuse and inspire the students."

A survey by the Council of Heads of Medical Schools found that nearly a quarter of all state-funded professorial posts were vacant, as were 145 senior lecturer and 177 lecturer posts.

Academic recruitment is difficult across all specialities, but especially in pathology, psychiatry and surgery, the conference was told.

Professor Ian Gilmore, registrar of the Royal College of Physicians, said clinical academics were being put under too much pressure. They routinely work at least a 64-hour week: 32 hours for the NHS and 32 for their university. But the need to treat patients, teach students and conduct research meant that they had almost irreconcilable demands on time.

Professor Janet Finch, vice-chancellor of Keele University, which is opening a new medical school, said she was seriously worried about being able to recruit enough clinical academics to teach the students.

Dr Smith and Professor Stephen Tomlinson, vice-chancellor designate of the University of Wales, both warned the conference that politicians from all parties had so far failed to grasp the extent of problems in recruiting clinical academics.