Heads of medical schools fear that the government intends to cut medical degrees from five years to four as part of its drive to get more doctors into the National Health Service quickly and cheaply.
Michael Powell, executive officer of the Council of Heads of Medical Schools, said: "We are totally opposed to the introduction of four-year courses for school-leavers. Any changes to the degree must be for sound educational and not financial reasons."
Four-year medical degrees are available for some graduates.
The NHS plan, published in July, called for "proposals for shortening the medical undergraduate course to three years for graduates and four years for others".
In a debate in the House of Lords last month, Lord Winston asked for reassurances that the government was not intending to shorten the medical curriculum to four years. Health minister Lord Hunt said that he would seek clarification on the issue. Lord Winston is still waiting for a response.
This week, a spokesman for the Department of Health said: "The NHS plan did propose some areas for potential reform, including the length of medical undergraduate courses. Officials are planning to hold a discussion with representatives of the key stakeholders."
He added: "The department would not contemplate any proposal that might undermine the high standards of medical education that have always been required for registration."
Mr Powell said: "They are keeping their options open."
Robert Boyd, principal of St George's medical school and pro vice-chancellor for medicine within the University of London, said: "The medical curriculum could not be fitted into four years and fulfil the requirements set out in the General Medical Council's Tomorrow's Doctors . Such a short course would not safeguard the public."
Sir Martin Harris, chairman of the Committee of Vice-Chancellors and Principals' health committee, said: "We welcome exploratory talks on more flexible routes into medicine, but not the shortening of medical degrees as a whole."
He added that a four-year degree would probably not meet European standards.
It is understood that ministers have been influenced by medical degrees in the United States, which are shorter.
Fears were raised about the quality of medical school courses this week after Nottingham, Leeds and Sheffield only just avoided automatic reinspection after the teaching quality assessments by the Quality Assurance Agency. Oxford and Cambridge medical schools were found to have performed well below average for Oxbridge departments.
Nurse educators fear that the government is planning shorter courses for nurses by replacing the diploma with the new foundation degree.