One in five GPs plans to quit the health service because of rising disenchantment with the job - an exodus that doctors' leaders say would be catastrophic and could lead to areas without a family doctor.

The new figures from a Department of Health-funded body are bound to dismay the government, which has launched several initiatives to recruit GPs and persuade existing family doctors to stay on. The research showed a worrying increase in the numbers wanting to quit, from 14% in 1998 to 22% in 2001. Most alarming is the main reason why GPs want to go - plummeting job satisfaction, according to the study in today's British Medical Journal.

The national primary care research and development centres at Manchester and York universities, which carried out both this study and 1998's, acknowledge that not all the doctors who say they want to leave will. But previous research has shown that many will do so. "If as few as half of those reported here do actually leave, this would still be cause for concern, given the current shortage of general practitioners," they say.

There were 30,860 GPs in the NHS as of March last year, according to a Department of Health census. The national plan for the NHS says 2,000 extra GPs and 550 extra trainees are needed. A Department of Health spokeswoman tried to play down concerns yesterday, saying that, thanks to a recruitment and retention drive, "we have already got more GPs than ever before".

But those in the profession point out that the headcount is misleading, because more and more are choosing to work part-time. The three-month vacancy rate last March had risen from 1.7% in 2001 to 2.8%. The government has boosted the number of GPs in training to 1,883, which is a record high, with incentives such as "golden hello" payments and greater flexibility, particularly for those with children. But there remain big questions over retention.

The new research suggests that it is the government's reforms and the pace of change that are causing dissatisfaction. "The organisation and governance of general practice has greatly changed in recent years and doctors may be experiencing difficulty in adapting to these changes," says the paper.

"Previous large-scale reorganisation of general practice in 1990 provoked widespread discontent, and dislike of NHS reforms has been cited by many doctors as a reason for quitting practice. Job dissatisfaction among general practitioners may additionally reflect a more global discontent of doctors with their changing role in society."

Long working hours are a source of discontent, says the paper. Doctors from ethnic minorities and those serving urban and deprived populations may experience lower job satisfaction, and men are more likely to be dissatisfied than women. Older doctors were more likely to say they planned to leave, but even the proportion of under-35s planning to go rose from 4% to 6%.

John Chisholm, chairman of the BMA's general practitioners committee, said the findings were worrying but not surprising. If large numbers of GPs were to quit, "it would have a catastrophic impact on the health service", he said. "We are already seeing major problems in recruiting new GPs and that is happening in all sorts of areas, from the prosperous leafy shires to deprived communities.

"If that number of doctors did retire, we would probably find they were very unevenly distributed across the country. We would be almost creating no-go areas where it would prove almost impossible to recruit."

The GP workload was increasing, he said, and so was the complexity of the work as the borderlines between hospitals and GP surgeries became blurred. GPs are increasingly being asked to take on semi-specialist clinics and minor operations. To help them cope, some of their traditional tasks are being shifted towards nurses and pharmacists.

Negotiations are under way for a new GP contract, which Dr Chisholm hopes will deliver greater job satisfaction. It was due to be concluded by the end of last year but has now slipped to February.

"The fundamental things are to allow GPs to control and manage their workload better than they can at the moment and that does include more time with individual patients, rewarding practices for the quality of the care that they deliver and allocating resources according to the needs of the practice population," he said.