Family doctors are threatening to desert the NHS and charge patients £25 for an appointment.
Union officials said Britain's 30,000 GPs - among the best-paid in Europe - should consider resigning en masse if the Government persists in trying to get them to work longer hours in the evening and at weekends.
In a leaked document, the British Medical Association said that any walk-out would have to take place soon if it were to be effective, before ministers were able to prepare alternative private provision.