There is concern for patient safety
The NHS in England and Wales is failing to ensure patient care is "as safe as it reasonably could be", the head of the Healthcare Commission has said.
In its annual report, Sir Ian Kennedy said the NHS was "only just out of the starting blocks" on the issue.
He warned there was a "black hole" of information on the quality and safety of general practice care.
But primary care and safety organisations said the watchdog had been looking at out-of-date data.
The assessment of the health service is the last to be published by the commission before it is wound up and its work handed over to the new Care Quality Commission (CQC) in March next year.
The commission said research into general practice safety suggested incidents were far more common than actual data showed - what it called the information "black hole".
The report also highlighted 22 "recidivist" trusts, around 5% of the total, which continue to perform poorly.
It said management and leadership were problems in some, while others had difficulties because of their rural settings.
Sir Ian said: "There are a small number of trusts trapped at a level of performance that is unacceptably poor."
But Sir Ian said safety was the priority.
"There's a great deal to do before we can be confident that the care that patients receive is as safe as it reasonably could be."
He added: "We are a long way from an NHS which systematically and hungrily examines its performance, reinforces safe practice, gets in and learns from things that go wrong and does things differently and more safely as a consequence."
Sir Ian said a culture where mistakes could be reported and learned from should be "internalised in the DNA" of NHS trust boards.
And he said the CQC would have to focus particularly on GP care.
"The vast majority of that care is safe and of good quality, but that's as far as we can go," Sir Ian said.
"We still don't know very much about how safe care in primary care is.
"Information on things such as missed diagnoses or late diagnoses won't show up in anyone's register of incidents because there isn't an incident, just a black hole."
The Healthcare Commission highlighted 2003 research which suggested medical errors occur in primary care anywhere from five to 80 times per 100,000 consultations (so between 40 and 600 errors a day) - up to 20% of which are thought to cause harm.
But it said that just 0.3% of incidents occurring in England and Wales in 2007/08 were from general practice, even though the vast majority of the contact a patient has with the NHS is with a GP.
However the British Medical Association said the commission's criticisms were out of proportion.
Chairman Dr Hamish Meldrum said: "Unfortunately, the report contains the misleading suggestion that up to 600 errors occur in primary care a day.
"This is based on data which was mainly gathered outside the UK, and identified that medical error occurs between five and 80 times per 100,000 consultations.
"Any errors are regrettable but there are millions of contacts between the NHS and patients every day.
"It is inevitable that, in a very small proportion of these, care falls below the highest standards.
"Doctors want to get rid of unacceptable variations in quality, but we need to be careful to analyse and learn from the causes of low performance rather than jumping to conclusions or simply adopting a blame culture."
The National Patient Safety Agency, set up by the government, stressed the majority of incidents reported were not serious.
It said that between April 2007 and March 2008, of 855,845 incidents reported, 93% resulted in no or a low level of harm to patients, 6.9% resulted in moderate or severe harm and 0.4% led to the patient's death.
Health minister Lord Darzi said work was under way to improve safety standards and introduce easier ways for front-line staff to report patient safety incidents.