About 840 people a year die in English hospitals due to lapses in safety such as having a fall, being given wrong medication or medical equipment failing, an official report suggested yesterday.
The National Patient Safety Agency said its figures were likely to be an underestimate and only represented the first steps in assessing how serious such problems are within the NHS.
A national reporting scheme is not yet fully in place, and there is a lot of uncertainty about how widely the system has been used so far.
There is also debate worldwide about the extent to which safety incidents contribute to cases of serious harm or death. Mistakes might not be to blame in the cases of people who died from their underlying condition. The system launched less than two years ago also does not include, for instance, most deaths linked to MRSA infection.
The agency was keen to stress that seven in 10 safety incidents had no effect on a patient. In only 1% of an estimated 572,000 incidents in a year did patients die or suffer serious harm.
Official reporting of incidents in England and Wales only started in November 2003, and is still far from universal, although the agency says the system is the most advanced in the world.
Data collected up to March this year suggested there were 85,342 incidents involving 86,142 patients. Information about English hospitals within those figures has been extrapolated by the agency. Eventually it is hoped all aspects of the NHS, including GP surgeries, ambulance services and mental health services will be covered.
Richard Thomson, the agency's director of epidemiology and research, said: "It must be remembered that the great majority of NHS care is safe and effective, with more than 1 million patients successfully treated every day. However, it is inevitable in complex healthcare systems, treating often very sick patients, that sometimes things can and do go wrong."
Data from the reporting system would be combined with information from confidential inquiries, litigation, doctors, patients, and the public to build a more complete picture, said Prof Thomson. He stressed however that those NHS trusts which reported most incidents are not necessarily less safety conscious than others; indeed, they might take the issue more seriously.
"The number of incidents is of the same order of magnitude as previously quoted estimates of 850,000 adverse events a year, but the number of deaths is considerably lower than the widely quoted figure of 40,000. Our analysis of reported deaths ... will contribute to the debate about the size of the problem, but further research is needed to arrive at a more precise figure.
"Nevertheless each death is a tragedy for the patient, their family and indeed for the staff involved. We are committed to working with the NHS to prevent such tragedies."
Sir Liam Donaldson, the chief medical officer, is the chief architect of the system. Earlier this week he questioned the commitment of some parts of the NHS to acting on official safety warnings. "We must ensure that when patients are harmed, sources of risk are identified, solutions are implemented, and lessons are learned. But we can only do this if we know what is going wrong."
Peter Walsh, chief executive of Action against Medical Accidents, said that it was encouraging to see reporting of incidents was increasing. "Unfortunately though, large numbers of medical errors still go unreported or undisclosed to the patients or their family.
"It is imperative that NHS organisations became more open and honest when there has been an incident or omission in treatment which causes harm."
Recent safety investigations included problems with anticoagulant drugs, including interaction with other medication, following 311 incidents and two deaths.
Misusing equipment on crash-call trolleys has also put critically ill patients at risk, while at least four people have died on wards due to poor management of patients with tracheostomies, where openings are made in the windpipe to aid breathing.
