By Nick Triggle
Health reporter, BBC News
Private clinics carrying out NHS care are not seeing as many patients as they should, but they are still getting paid as their income was guaranteed.
Scans form part of the services commissioned
Private treatment centres were set up to do minor surgery and diagnostic tests, in a bid to cut waiting lists.
Figures show that just four of the 25 such clinics created in the first wave of openings are doing enough work.
The government said the clinics would be making up the shortfall in work in the future.
There have been two waves of ISTCs (Independent sector treatment centres) opened since the concept was announced in 2003.
The clinics tend to concentrate on treatment such as knee and hip replacements, hernias and cataract operations.
Some are only doing 50% of the work specified in their contract.
The first group were given guaranteed contracts by the government to entice them into the health service.
This caused anger in the NHS as hospitals do not get such promises and instead have to compete for patients as they are paid per person treated.
When ministers announced the second wave of centres, they said they too would only be paid per patient.
Some of the second wave have now been scrapped because of a lack of demand and ministers have announced there will be no third wave.
But because of the nature of the guarantees given to the first group, the government has to pay the full amount of the contract regardless of how many patients the centres see.
The Department of Health figures to the end of September showed just four centres were operating at 100% of the value of their contract.
Three centres in Oxford, East Cornwall and Milton Keynes were fulfilling less than 60% of the value of their contract and one, in Kent, was under 50%.
On average, 84% of the value of the 25 contracts - worth over £1.2bn in total - were being fulfilled.
Most of the deals are for five years and many are about half-way through.
The government said it believed the centres would be able to catch up.
And a spokeswoman added: "There is no doubt the independent sector has helped improve health services for patients, speed up treatments, reduce waiting times and galvanise the NHS to raise its game.
"ISTCs that are new to the local health economy take time to build up the number of procedures they do."
But Jonathan Fielden, chairman of the British Medical Association's consultants committee, said: "The contracts were poorly designed and these figures show that. They are wasting taxpayers' money."
And Karen Jennings, head of health at Unison added: "We now have the spectacle of millions of pounds being paid out to private companies for operations that never take place.
"This is money that should have gone into the NHS."
But David Worskett, director of the NHS Partners Network, which represents private health providers, said: "Some are a little short of what we would want.
"One of the problems is that in some areas GPs are suspicious of the centres and are not referring patients to them.
"We have found once they do both patients and GPs are satisfied."