Last December the IPPR produced the Future Hospital report, calling for the NHS to concentrate services in larger centres of excellence. It was significantly quoted by prime minister Tony Blair.
However a study from Keep Our NHS Public said the IPPR's claims are 'at best inconclusive'.
In The Case for Hospital Configuration: not proven, professor David Byrne from Durham University and Sally Ruane from De Montfort University say the think tank omitted significant reviews that concluded there was no relationship between volume of procedures and outcomes, so bigger hospitals would not save money.
They also suggest the IPPR made the recommendations because one of the report's co-sponsors, Prime - a major NHS and social care building company - could benefit. Author Sally Raune said: 'Reconfigurations conveniently create opportunities for powerful interests.'
An IPPR spokesman defended its report, saying the paper had referenced two systematic reviews and demonstrated the benefits of concentrating services. 'Byrne and Ruane fail to provide evidence to counter this. The evidence they cite actually supports the case for concentrating care provision,' he said.
He also denied any unethical relationship with Prime: 'The conclusions are the responsibility of the authors alone and do not represent the views of any of the funding partners. We have contractual agreements which make this clear.'