Stark increases in GP workloads are "unsustainable", researchers have said after a new study showed that family doctors are dealing with more consultations than ever before.
Workloads in general practice have increased by 16% over the last seven years, according to the largest ever analysis of GP and nurse consultations.
Doctors' leaders said general practice was in "crisis" after the study showed that family doctors in England are dealing with more frequent and longer consultations at the same time as the rate of GPs has decreased.
The authors of the study, published in The Lancet, warned that general practice is nearing "saturation point".
"For many years, doctors and nurses have reported increasing workloads but, for the first time, we are able to provide objective data that this is indeed the case," said Professor Richard Hobbs, lead author from the Nuffield Department of Primary Care and Health Sciences at the University of Oxford.
"The demands on general practice have increased substantially over the past seven years. Recruitment of new GPs and nurses remains low while the population in England steadily increases.
"As currently delivered, the system seems to be approaching saturation point."
The study, based on analysis of more than 100 million GP and nurse consultations at 398 general practices in England between 2007 and 2014, found the average number of annual consultations per patient rose by 13.67% for doctors, with the average patient now seeking almost four GP visits each year.
The number of nurse consultations rose by 2.76%.
The number of face-to-face GP consultations rose by 6.38% and the number of telephone consultations nearly doubled.
Average consultation time has also increased, with most appointments lasting almost nine minutes.
The authors warned that, as the time spent with a patient nears the 10-minute allocated slot, doctors and nurses have little time to perform other duties before seeing other patients.
Although the total number of GPs increased over the study period, the authors said that this actually represents a 1% decrease in the number of GPs per patient - from 60.9 GPs per 100,000 patients in 2007 compared with 60.6 in 2014.
Professor Hobbs added: "Current trends in population growth, low levels of recruitment and the demands of an ageing population with more complex needs will mean consultation rates will continue to rise.
"In 2015, GPs in England reported having the lowest job satisfaction rates since records began in 2001. NHS plans to recruit an additional 5,000 GPs will take some time and crucially depend on an improved appeal of general practice as a career choice.
"There are few short-term solutions, but reducing the time doctors need to spend on non-clinical duties may help ease the workload temporarily. More research is urgently needed to fully estimate the knock-on effects of increased workloads in general practice on other sectors of the health system."
Commenting on the study, Dr Maureen Baker, chairwoman of the Royal College of GPs, said: "This report should ring alarm bells for the Government and spur ministers into action to address the crisis in general practice before it's too late.
"For too long GPs have been expected to do more and more for less and less and this perfect storm of rising demand, plummeting resources and not enough GPs can no longer be no longer be ignored.
"GPs and our teams are making more consultations than ever before, and our patients are living longer and with multiple long-term conditions, meaning that our workload is growing in complexity as well as volume.
"GPs are responding to demand by offering different types of appointments, such as phone consultations, but, despite our efforts, demand is rising so acutely that this is having little effect in terms of our workload. And the increasing complexity of our work means that the standard 10-minute appointment is increasingly unfit for purpose.
"But there is a limit to how much more GPs and our teams can do, safely, with the resources available. This pressure is not only bad for GPs, as job satisfaction for general practice plummets, but for our patients, who might be finding it consistently difficult to make a GP appointment. There is also a very real link between rising levels of GP fatigue, and our patients' safety.
"The Government must take note of the College's calls for general practice to receive 11% of the overall NHS budget and urgently implement all aspects of the 10-point plan to build the GP workforce."
Dr Richard Vautrey, deputy chairman of the British Medical Association's GP committee, said: "This study provides clear evidence which supports what every GP and patient knows: GP practices are working harder than ever before, but are struggling to provide even basic levels of care as they are overwhelmed by unsustainable workload.
"In many cases this is beginning to put patients at risk as services become overstretched, while an understaffed GP workforce is being further depleted as staff leave owing to burnout and stress.
"A BMA survey shows that nine out of 10 GP practices are reliant on temporary staff to provide enough appointments to patients, with shortages even being reported amongst these GP locums.
"The Government has to reverse a disastrous approach that has seen the proportion of NHS funding devoted to general practice dropping from 10.5% to 7.5%. This is starving GP practices of resources and exacerbating shortages in appointments. We need an urgent, sustained package of support for general practice that prevents GP services collapsing completely."
A separate study looking into the work of ambulance dispatch staff found that many feel "overloaded and undervalued" and have a high rate of sickness as a result.
The paper, published in the Emergency Medicine Journal, found the average sickness rate for workers in the sector was 6.78% between January and March 2014, compared to a national average sickness rate of 1.6% for men and 2.6% for women in 2013.
Researchers compiled feedback from Emergency Medical Services dispatch staff, who receive information from call handlers, assess the emergency situation and resources available and send help accordingly.
Professor Patricia Schofield, from Anglia Ruskin University, said: "It is a role that requires a split-second decision based on changing factors, with the knowledge that it could be a life-or-death situation. They really are some of the unsung heroes of the NHS.
"The staff interviewed said they enjoy their work and take great pride in the job that they do but admitted that, despite an increasing workload, they felt overlooked and marginalised by other people within their organisation and perceived as 'faceless'.
"With sickness levels among healthcare staff currently the highest in the public sector, it is important to understand the difficulties that these workers face and find ways of reducing the stress they find themselves under."