Problems with a computer system upgrade have caused a backlog of thousands of patients at one hospital trust, who must now wait six months or more for hospital tests or treatment.
Department of Health regulations hold that patients should not have to wait for hospital treatment for longer than 18 weeks from the time they are referred by a GP.
More than 14,000 people at a major London trust have already encountered waiting periods that breach government standards, according to a report in the Times.
The backlog of electronic patient records on an 18-week waiting list has topped 26,000.
"It has been a frustration for everyone at Barts and The London NHS Trust that our desire to meet the 18-week national target has been compromised by previous weaknesses in our information management and administration systems," a spokeswoman for the trust said in a statement.
The system was introduced by Barts and the London NHS Trust in April last year, and is a forerunner to the many electronic patient record systems currently being installed across the country as part of the 12.6 billion NHS IT upgrade.
The problems are the result of glitches in the Cerner Millennium CRS, combined with flawed data and procedures. The trust said the sheer size of the backlog will make it very difficult to clear, but it is committed to doing so by the end of the year.
"The overall number of patients not treated within 18 weeks of referral has reduced, and continues to do so, month-on-month, as a result of extensive work by the trust to ensure patients are both seen and treated in the target time, as well as ensuring that data relating to all patients is accurate and avoids duplication," the spokeswoman said.
"There is no evidence that any patient has come to clinical harm because of the backlog," she added.
