Clinical trial results are being routinely withheld from doctors, which is undermining their ability to make informed decisions about how to treat patients, the Commons public accounts committee has warned.

MPs have raised “extreme concern” that manufacturers appear to only publish around 50 per cent of completed trial results and warned that the practice has “ramifications for the whole of medicine”.

Research suggests that trials giving a favourable verdict are about twice as likely to be published as trials giving unfavourable results, the committee said.

Experts have failed to agree on how well flu drug Tamiflu works but discussions have been “hampered” because important information has been held back, it added.

Figures released last year showed the Department of Health spent £424m on stockpiling Tamiflu but had to write off £74m of its stockpile as a result of poor record-keeping by the NHS.

A review carried out by the Cochrane Collaboration into 20 existing studies into the drug found it ”did not reduce influenza-related lower respiratory tract complications” but did induce nausea.

It is now receiving full clinical study reports from manufacturer Roche, which are being used to complete a further review of the effectiveness of Tamiflu. The results of that should be used by government, the Medicines and Healthcare Products Regulatory Agency and the National Institute for Health and Care Excellence to review the drug’s use, MPs said.

They also called on ministers to take action so full trial results are available to doctors and researchers for all treatments currently being prescribed and carry out regular audits of how much information on how much information is being made available.

PAC member Richard Bacon said: “The full results of clinical trials are being routinely and legally withheld from doctors and researchers by the manufacturers of medicines.

“This has ramifications for the whole of medicine. The ability of doctors, researchers and patients to make informed decisions about treatments is being undermined. Regulators and the industry have recently made proposals to open up access, but these do not cover the issue of access to the results of trials in the past which bear on the efficacy and safety of medicines in use today.

“Research suggests that the probability of completed trials being published is roughly 50 per cent. And trials which gave a favourable verdict are about twice as likely to be published as trials giving unfavourable results.

“This is of extreme concern to this committee. The department and MHRA must make sure, both prospectively and retrospectively, that clinical trials are registered and the full methods and results of all trials are available for independent wider scrutiny by doctors and researchers.

“There is also no routine sharing between NICE and the MHRA of information provided by manufacturers during the process of licensing medicines.

“There is still a lack of consensus over how well the antiviral medicine Tamiflu, stockpiled for use in an influenza pandemic, actually works. The lack of transparency of clinical trial information on this drug to the wider research community is preventing proper discussion of this issue among professionals. We are disturbed by claims that regulators do not have access to all the available information.

“The case for stockpiling antiviral medicines at the current level is based on judgment rather than on evidence of their effectiveness during an influenza pandemic. Before spending money in future to maintain the stockpile, the department needs to review what level of coverage is appropriate. It should look at the level of stockpiling in other countries, bearing in mind that the patent for the medicine runs out in 2016.”