GPs' patients are not receiving the best care they could be because of a new government target, a report says.
GPs now have to see patients within 48 hours under a new target
Patients should only have to wait 48 hours for an appointment under a target which must be met this year.
But the report, by the NHS Alliance and Royal College of GPs, said it was "too simplistic" and should be scrapped.
The target fails to meet the needs of people who need to see a GP that day or want to make advanced appointments, the study said.
It also said the target meant practices with a number of partners could not always guarantee patients appointments with the same GP.
Continuity of care, which was important for patients with complex medical and psychological needs, was jeopardised as a result, the study said.
And it revealed some GPs have stopped taking appointment bookings in advance to keep their time free to meet the 48-hour requirement.
The target also damaged the role GPs played in the management of chronic care.
Instead, the report called for it to be replaced by a system which took into account the complex needs of patients.
According to latest government figures, 97% of patients are now able to see a GP within 48 hours compared to only half seven years ago.
Professor John Campbell, of the Peninsular Medical School in Exeter, who edited the report, called The Future of Access to General Practice-based Primary Medical Care, said "What we are saying is targets have their place but if you have a target that is over simplistic then that does not work.
"The target has stimulated a lot of debate. A lot of people can now see their doctor more quickly.
"But there are trade-offs and disadvantages.
"Patients tell us they like to see the same doctor but one effect of the target is that this is not always possible.
"Without the continuity of care, patients are not being served in the best way they could be."
NHS Alliance chairman Dr Michael Dixon said NHS policy needed to reflect that not all patients were the same.
"What we are proposing will make life more difficult for the planners but better for patients.
"We have to stop behaving as if patients are all the same square-shaped pegs we can force into the same square hole."
And Professor David Haslam, the chairman of the Royal College of GPs, added: "People visit their GPs for a variety of reasons.
"But the current target system is not delivering according to patient needs and assumes that all patients are the same.
"Worse still, it puts pressure on GPs to disregard their different needs."
Shadow health secretary Andrew Lansley said the government was obsessed with setting targets and promised a Conservative administration would get rid of targets that got in the way of treating patients.
"GPs should be given the freedom to decide which patients need urgent attention, and those who can wait longer than 48 hours."
But Health Minister John Hutton defended the target, saying it had benefited patients.
"Patients want to see their GP as quickly as possible. The target has helped ensure that this happens.
"The 48-hour target is therefore all about improving patient-centred care, because the longer a patient has to wait to see a GP, the more anxious they are likely to become."
And Michael Summers, the chairman of the Patients Association, said the majority of patients favoured the target.
"The system used to be that you had to wait a long time to see a GP.
"I think targets are sometimes helpful, if you don't have them it can be a free-for-all and doctors can do as they please.
"But obviously there are downsides too."
The report also looked at several other areas of GP work.
It said reception staff were an "untapped" resource and their role should be developed more.
It also called for more use of web-based technology.
Only 157 out of 8,500 GP practices have broadband access.