The financial benefits of sending NHS patients to private health treatment centres have not been proved, according to Edinburgh University academics.
Academics say using private sector services could reduce NHS jobs
Professor Allyson Pollock and Sylvia Godden have studied NHS use of mobile treatment centres run by the private sector for the past three years.
In an article in the British Medical Journal they warned that the programme would contribute to NHS deficits.
The practice has been used in parts of Scotland to try to cut waiting times.
Under the previous Scottish Government administration, the NHS in Scotland made increasing use of mobile surgery centres, hired from the private sector, for relatively simple operations such as cataract removals.
NHS Tayside also went into partnership with the private sector at Stracathro hospital near Brechin.
But Ms Pollock and Ms Godden claimed there was so little data available from private treatment centres it was impossible to assess their contribution.
They also said the private sector was using NHS staff rather than employing staff from elsewhere.
The policy has caused instability in the NHS while diverting NHS funding into profit-making organisations, their article claimed.
"The policy of diverting scarce NHS funds into independent sector treatment centres is leading to fragmentation and financial instability and NHS beds and services are being closed to make way for the for-profit private sector, " said Professor Pollock.
"Despite assurances by the UK secretary of state for health, Alan Johnson, the available evidence suggests that the private sector is profiting at the expense of patients, the public, and the NHS."