The number of severe faults in NHS computer systems has almost doubled over the past three years.
Last year nationwide NHS computer systems suffered 820 severity-one or critical faults, up from 488 in 2006.
A severity-one fault is a problem affecting a system critical to patient care or affecting 5,000 NHS computer users or more.
The NHS attributed the rise to teething problems among the growing number of systems being rolled out across the NHS as part of the £12.7bn National Programme for IT (NPfIT) — parts of which have suffered technical difficulties and are years behind schedule.
The figures were revealed in a written parliamentary answer to Liberal Democrat MP Norman Lamb.
A spokesman for the NHS Connecting for Health service-delivery team said: "When you deploy a national system such as The Spine or Choose and Book, you will get some glitches as problems emerge and are discovered.
"As systems are upgraded with more functionality they are getting much greater use, and at the same time the number of deployed units has increased."
Connecting for Health's spokesman declined to say which systems had been affected by severity-one faults.
In October 2008 the number of critical faults in national IT systems jumped to 165, from 71 the previous month — a spike the spokesman attributed to "a set of issues affecting two systems" that had a "noticeable effect" on a number of NHS computer users.
"Other than the month of October 2008, the number of severity-one incidents each month has been fairly low, against a rate of increase of 10 to 11 per cent per half year in the number of systems deployed," he said.
The spokesman added that the number of severity-one faults could also be inflated by a tendency among users to categorise IT problems as being more severe, to prioritise the response, adding that faults were often recategorised as being less serious following further investigation.
The figures were revealed in the wake of a critical report into the NPfIT by the parliamentary watchdog, the Public Accounts Committee, which gave the Department of Health six months to speed up the rollout of a delayed NPfIT project, the Care Records Service, or risk seeing the scheme broken up.