Department of Health ministers have been accused of suppressing damaging reports in what is likely to ignite a fresh row about "spin".
The claims centre on a report on failures to properly decontaminate NHS hospitals to ensure against the spread of CJD – the human form of mad cow disease.
The full report was put on the department's website last week. It found uncontrolled use of chemicals and inappropriate use of processes. "These put patients and staff at risk and the organisation in potential breach of the law," said the report.
It also found few hospitals had an effective management control system in place. In some cases, the equipment was not adequate to carry out decontamination; records were not kept; and items designated for single use were sometimes re-used.
The early findings were ordered to be suppressed in an internal letter by the chief executive of NHS estates to Dr David Hurrell, a specialist in the field, which was published in a written Commons answer by public health minister, Yvette Cooper.
It said: "In the light of the somewhat negative outcome recorded by the visiting assessors at the majority of clinical centres, there is a need to ensure at the express request of ministers, that the final version and earlier draft reports remain strictly confidential."
The letter said progress on improving the sterilisation of possibly infected instruments would be "compromised if the findings of the report were to enter the public domain in an inappropriate or unauthorised form".
Dr Hurrell, who acted as technical coordinator for the project, was ordered to destroy all copies of the draft, including those copies held on computer.
Dr Evan Harris, the Liberal Democrats' health spokesman said: "It's bad enough, the Government spinning of information that should be publicly available, but the suppression of information involving public health is totally unacceptable.
"They admit they have suppressed the reports of their own working groups. What faith can we have in their work if the Government is keeping it secret from their own people?"Reuse content