There is no decent evidence that private treatment centres offer good value for money for the taxpayer, experts have argued.
Independent Sector Treatment Centres (ISTCs), which have contracts with the NHS, have caused controversy since they were introduced in 2003.
They were set up to cut waiting lists by carrying out surgery like hip replacements and cataract removal.
But they have come under fire for "creaming off" easy operations, leaving complicated cases to the NHS, and for their guaranteed income regardless of how many patients they see.
The researchers, writing in the British Medical Journal (BMJ), said taxpayers' money is still being spent on ISTCs despite no good evidence that they provide additional capacity, value for money or high quality care.
Professor Allyson Pollock and Sylvia Godden, from the University of Edinburgh, said the Government seems determined to "privatise the delivery of healthcare".
The ISTC programme for England, over the course of two phases (waves), will provide elective surgery and other services at a total cost of more than £5bn, they said.
In July 2007, 24 centres, provided by seven for-profit companies, were operational but there was no good data on the scale of their contribution, they wrote.
Another analysis by the National Centre for Health Outcomes Development on five providers found data so incomplete that attempts to compare the centres with agreed standards and benchmarks were "futile".
The Royal College of Surgeons of England has also reported "increasing evidence" that ISTCs are unable to manage complications, and patients are being readmitted to the NHS.
