Private clinics set up to carry out minor surgery have not brought major benefit to the NHS, MPs believe.
Cataract surgery is one of the operations carried out by ISTCs
A network of independent sector treatment centres (ISTCs) has been established in England to drive down waiting lists and increase choice.
The Commons health committee says waiting lists have fallen but this is more likely to be due to extra money in the NHS than the impact of the ISTCs.
It also warned that the programme could lead to cuts in services at hospitals.
To date 21 ISTCs have been set up at a cost of £5bn, although a number of NHS centres have also been established.
They carry out minor surgery, including hip operations, ear, nose and throat treatment and cataract operations.
It is hoped the private centres will eventually carry out 500,000 procedures each year. At present, they carry out around half that.
The first phase of ISTCs, announced at the end of 2002, were given guaranteed levels of work which has meant they could end up starving NHS hospitals of patients and putting them at risk in the current financial climate, the MPs said.
In phase two, unveiled in March 2005, ministers insisted they could only be built where there was local need.
However, the cross-party group of MPs said hospital services could still be cut and then replaced by the private clinics under the terms of the deal.
The report said the centres were "poorly integrated" with the NHS and were not training doctors.
They said putting the extra money spent on ISTCs into the NHS may have been a cheaper and more efficient option.
But it was hard to make firm conclusions as there has been no attempt to assess and quantify the impact of the centres, the report said.
However, the MPs also said there was no "hard evidence" to prove standards of care in ISTCs were lower than in the NHS - a common criticism of some professional bodies.
And it said while ISTCs have embodied good practice and innovative techniques, such standards could also be found in the NHS.
Committee chairman Kevin Barron, a Labour MP, said: "It is difficult to say how the ISTCs have affected either patients or the NHS due to the lack of any systematic assessment."
But he added the "ideological" opposition to using ISTCs must end.
Paul Miller, chairman of the British Medical Association's consultants committee, said doctors had been worried about the effect of ISTCs for years.
"I am delighted that the Health Committee agrees NHS hospitals are more likely to give better integrated care and to be cheaper," he said.
And Liberal Democrat health spokeswoman Sandra Gidley added: "This is yet another example of the government introducing powerful forces into the NHS without any prior assessment of the impact they will have on patient care."
Shadow health secretary Andrew Lansley said: "The whole purpose of ISTCs was to increase capacity and introduce competition but they have failed on both accounts."
Health Minister Lord Warner said ISTCs have "increased choice, offered earlier treatments and driven down prices".
And he added the government had already made moves to gather more information about ISTCs by asking the Healthcare Commission to conduct an audit of the centres.