However, it predicted the introduction of the Health and Social Care Bill, currently proceeding through Parliament, would encourage further private treatment in NHS hospitals.
The market analyst blamed recessionary pressures and the private patient cap for causing the 2% fall in private income to £430m in 2009/10 from £439m the previous year.
Overall since 2006/2007 there has been no growth in revenues.
Its NHS Trusts & Primary Care Trusts Financial Information report noted private healthcare from both insurance and self-paying patients was still suffering the effects of recession.
"Stalling growth reflects a clear dip in demand for private healthcare funded by medical insurance and from patients' own pockets, which has yet to recover from recessionary cutbacks," it said.
"In addition growth for Foundation Trusts is limited because their private patient income as a ratio of their total income is capped at 2003/2004 levels.
"UK private patient revenues have only risen by 9% in the five years since the cap was introduced. Looking forward, however, the proposal to remove this restriction in the Health and Social Care Bill, suggests more positive growth prospects from this source for the NHS," it added.
Figures in the report show that private patient income in the UK fell to just 0.6% of Trusts' total core income.
English trusts led the way, accounting for 96% of all private patient NHS activity across the UK and earned 0.7% of core revenues from the arena compared to Wales (0.2%) and both Scotland and Northern Ireland (0.1%).
The report also revealed the cost of employing agency and other temporary staffing in the NHS in England continued to rise as non-NHS staff spending reported by Trusts grew by 17.5% overall from 2008/2009.
However, it expects this trend to be reversed by 2014 in the face of ‘heavy pressure to realise massive cost savings under coalition government NHS reforms'.
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