The pharmaceutical giant Roche is being accused of irresponsibly withholding key trial data about a vital flu drug on which governments around the world have spent billions of pounds.

The anti-flu drug Tamiflu has been stockpiled by countries against the outbreak of a flu pandemic since 2004. The UK alone has spent £500m.

Yesterday, the British Medical Journal launched a campaign to persuade Roche to give doctors and patients the full data on Tamiflu, three years after doubts about its safety and efficacy emerged.

In 2009, researchers from the Cochrane Collaboration found that results of eight out of 10 key trials of Tamiflu were never fully published and concluded there was "insufficient data" to show it reduced complications – a vital factor in a pandemic which could save lives.

Roche promised to release the full data, but then reneged on its promise, according to the BMJ. The journal's editor, Fiona Godlee, published an open letter to Sir John Bell, the Regius Professor of Medicine at Oxford University and a board member of Roche, in which she appeals to him to use his influence to persuade the company to release the data "for independent scrutiny".

The two trials that have been published, she says, "were funded by Roche and authored by Roche employees and Roche-paid external experts" and "could not be relied on".

There have now been 123 trials of Tamiflu but 60 per cent of the patient data "remains unpublished", she says. "I am appealing to you as an internationally respected scientist and clinician and a leader of clinical research in the UK to bring your influence to bear," she writes.

"In refusing to release these data of enormous public interest, you [the company's directors] put Roche outside the circle of responsible pharmaceutical companies. Billions of pounds of public money have been spent on [Tamiflu] and yet the evidence on its effectiveness and safety remains hidden from appropriate and necessary independent scrutiny."

The European Medicines Agency announced last week that it was investigating Roche's alleged failure to report side-effects of some of its drugs in as many as 80,000 patients, following a review by the UK Medicines and Health Products Regulatory Agency. If found guilty, the company could be fined up to 5 per cent of its sales in the EU – which amounted to 8.2bn Swiss francs (£5.4bn) in 2011.

In the Commons, the Conservative MP Sarah Wollaston, a GP, called last week for drug companies to publish all clinical trial results, saying it was "vitally important for patient safety" and would give a "completely different evidence base for medicine."

The UK was among the first countries to place bulk orders for Tamiflu (and smaller amounts of Relenza, a rival drug made by GlaxoSmithKline) for stockpiling when fears about a possible avian flu pandemic emerged in 2003 and 2004.

The stockpile was used during the swine flu outbreak of 2009, but because the illness was mild in most people demand remained low.

Dr Godlee said yesterday: "Tamiflu was licensed over 10 years ago and has been in widespread use since. Once a drug is licensed it becomes a drug on which public money is spent and lives may be put at risk. Inevitably if there is information we are not allowed to see we wonder what is in there. There is a legitimate scientific question [about its safety and efficacy] which can only be answered by looking at the data. It is just shocking."

A spokesman for Roche said: "Roche provided the Cochrane group with access to 3,200 pages of very detailed information, enabling their questions to be answered. Roche stands behind the robustness and integrity of our data supporting the efficacy and safety of Tamiflu."