The value of private clinics to reduce NHS waiting times has been called into question after an analysis shows the only centre in Scotland may have been paid up to £3m for non-treatment.

The study found that NHS Tayside paid the Scottish Regional Treatment Centre for a minimum number of monthly referrals, regardless of the actual number, and for referrals whether or not patients went on to receive treatment.

According to Allyson Pollock and Graham Kirkwood of Edinburgh University, the SRTC, run by Netcare, carried out work worth 18% of the annual £5.7m contract, although NHS Tayside has claimed the figures are "fundamentally inaccurate".

"This contract shows the complex payment mechanism increases the risks and costs to the health boards," they say in their paper in the British Medical Journal.

The analysis was conducted after information was released under the Freedom of Information Act. Different FOI rules in England allow the Department of Health to keep the contracts confidential.

"If the contracts are the same as in Scotland … one might ask whether the same results are applicable," Pollock said.