Roche, the manufacturer of Tamiflu, has made it impossible for scientists to assess how well the anti-flu drug stockpiled around the globe works by withholding the evidence the company has gained from trials, doctors alleged today .

A major review of what data there is in the public domain has found no evidence Tamiflu can prevent healthy people with flu from suffering complications such as pneumonia.

Tamiflu may shorten the bout of illness by a day or so, the investigators say, but it is impossible to know whether it prevents severe disease because the published data is insufficient. Roche has failed to make some of the studies carried out on the drug publicly available, the scientists say.

"Governments around the world have spent billions of pounds on a drug that the scientific community now finds itself unable to judge," said Dr Fiona Godlee, editor of the British Medical Journal, which published the new review online and collaborated in a joint investigation with Channel 4 News, shown this evening .

Roche has made a fortune out of the drug, with sales of £1.6bn this year alone. The British government has stockpiled enough for half the population.

In the review, Professor Chris Del Mar, from Bond University in Australia, analysed 20 published trials that focused on prevention, treatment and adverse reactions. The authors say they were hampered by the "paucity of good data".

The reviewers were forced to leave out eight trials because they had not been published, and Roche offered them "under conditions we thought unacceptable, and what was offered to us was insufficient to analyse properly."

Because they did not have full access to all the trials, the reviewers say previous evidence on the effects of Tamiflu and other drugs of this class (the neuraminidase inhibitors) may be unreliable. They call on governments to set up studies to monitor the drugs for safety.

A second review was carried out in the UK at Birmingham University by Professor Nick Freemantle and Dr Melanie Calvert, who analysed a series of observational studies Roche provided. (These are studies of people who took the drugs, but without a comparison group of people who did not take them.

Although the reviewers had doubts about the data, they say it is possible Tamiflu reduced the risk of pneumonia. But if so, the benefit was small and there were side-effects to consider.

Freemantle said he saw "very little evidence to support the widespread use of oseltamivir in the otherwise healthy population who are developing signs of influenza-like illness."

He added: "We have remarkably few resources in this country to spend on pharmaceuticals on health, and it is surprising to see such widespread use of oseltamivir. But I suppose that once you've gone and bought lots of doses, then it's a bit like the situation with gun control in the US. If you have a gun in the house, it is much easier to use it. But it does not mean it's the right thing to do."

Dr Godlee and Professor Mike Clarke, director of the UK Cochrane Centre, call in the BMJ for new global legislation to ensure all trial data on drugs that have been granted a licence must be published in full.

Roche said in a response that it firmly believed in the robustness of the data. The company said governments and licensing authorities had been given access to all the trial information.

Roche has now undertaken to put summaries of all the Tamiflu study data on a password-protected site.