Poor and late hospital discharge information is putting patients at risk, GPs say.
Hospitals are supposed to send discharge data to GPs
Hospitals are supposed to send doctors information on medicine and treatment as soon as a patient is released, in order to help in their follow-up care.
But an NHS Alliance poll of 651 GPs found 70% often received papers late and many said the forms were not complete, compromising safety.
The government admitted there was work to do to ensure better communication.
GPs are meant to receive discharge summaries within two days of a patient being discharged.
It is either e-mailed, faxed or given to the patient to hand over.
As well as being late, family doctors had reported they often lacked important details, the NHS Alliance, which represents the interests of GPs, said.
Among information which was reported to be missing were the patient's name, contact details, medication and treatment.
Incorrect or insufficient data on medication, such as potentially toxic drugs like warfarin, has even led to patients being readmitted to hospital because of complications such as internal bleeding and strokes.
In one instance, a discharge summary was received but failed to mention that the patient had just spent a week in intensive care following a stroke and heart attack.
Some 58% of GPs reported the problems meant clinical care was compromised in the last year, with 39% claiming it had put patients at risk.
But nearly two-thirds of doctors said they had hospital teams in their areas who provided good, prompt information, proving it could be done.
The results come at a time when patients are spending less time in hospital following treatment as part of a government drive to move care away from hospitals and into the community.
NHS Alliance chairman Dr Michael Dixon said: "We need urgent action at national and local levels. The NHS cannot continue to allow patients to be put at risk just because too many hospitals regularly fail to get information to GPs when patients are discharged."
Patients Association chairman Michael Summers said: "We have long-standing concerns about the quality of discharge information. It can have very serious consequences, especially for elderly people."
But Gill Morgan, chief executive of the NHS Confederation, which represents hospitals, said: "There is often a variable standard between the notes provided. However, there is also variation in the standard of GP referral letters to hospitals."
She added electronic discharge summaries - being introduced as part of the 10-year NHS IT upgrade - "should go some way to helping overcome these issues".
A Department of Health spokeswoman said officials were looking to draw up a contract for hospitals in a bid to improve discharge information.
She added: "Patient safety is always top priority for the NHS but clearly there is still some work to do to ensure that information provided to GP practices about their patients is done quickly and accurately in all parts of the NHS."