One in four family doctors wants to leave general practice in the next five years and almost half intend to retire before the age of 60, the biggest survey of GPs in a decade suggests.

Growing demands from patients and increased bureaucracy have contributed to what the British Medical Association described yesterday as "horrendously low" morale among Britain's 42,000 family doctors. The findings will make gloomy reading for ministers who need to extract more work, not less, from the medical profession if the Government is to keep its promises set out in last year's NHS plan.

Although doctors have frequently complained about the state of the health service since it was founded more than 50 years ago, most observers agree that the position now is as bad as it has ever been.

The findings are also gloomy news for patients, with increas-ingly desperate doctors seeking ways to cut their workload. John Chisholm, the chairman of the BMA GPs committee, said: "The NHS cannot afford even for a moment to lose a tiny fraction of its workforce when it is facing a workload and recruitment crisis."

More GPs and support staff were urgently needed but could not be found overnight, Dr Chisholm said. Immediate measures needed to be taken, including curbing demand. "Some demands currently made of GPs are inappropriate. We need to look at demand management," he said.

Simon Fradd, a BMA negotiator, said the number of GPs intending to take early retirement had grown threefold in the past five years and was "disastrous. There is no doubt that an unmanageable workload is the driving force behind the despair many GPs are experiencing. Too much is being asked of too few." Dr Fradd said the health service had be be used in a more appropriate way. "There is not enough recognition that minor, self-limiting illness is common and that serious life-threatening illness is rare. We need to work with the public to understand the risks and to 'de-medicalise' those problems and manage them away from the surgery, at home."

He warned ministers to resist raising expectations that could not be met. A key source of doctors' anxiety for the future was the pledges made in the NHS plan, including a guarantee that all patients would be given a routine GP appointment within 48 hours. While admirable, that would require 10,000 extra GPs by the BMA's calculation when the plan allowed for only 2,000.

"We must stop raising expectations that cannot be met within the NHS in an appropriate way. Everyone knows the current level of resourcing is going to be insufficient to meet all needs. We believe there should be a continuing public debate about what the NHS will and will not provide."

The results showed 88 per cent of GPs supported the NHS, provided the workload of GPs could be reduced. But almost a quarter thought there should be a "substantial expansion" of private practice. List sizes had fallen from an average of 2,500 in the 1970s to 1,800 today but workload had grown because more care was now provided outside hospitals, the BMA said.

The survey, run for the BMA by ERS Market Research, included more than 50 questions dealing with job satisfaction, the state of the health service and aspirations for the future, and drew a 55.5 per cent response rate. The BMA said that was "very high" for such a detailed survey and insisted the results were representative.