Roche has offered an olive branch to scientific critics in a bid to end a bitter row over blockbuster flu drug Tamiflu that has led to calls for a boycott of the Swiss drugmaker's products.

Tamiflu has been approved by regulators worldwide and stockpiled by many governments in case of a global outbreak - but some researchers claim there is little evidence it works and have lobbied since 2009 for Roche to hand over all its data from clinical trials.

Sales of the drug hit close to $3 billion in 2009, due to the H1N1 swine flu pandemic, although they have since declined.

Roche's pharmaceuticals head said on Thursday he had written to the Cochrane Collaboration, a non-profit group that reviews trial data to assess the value of drugs, offering to set up a multi-party advisory board to review all the Tamiflu data.

The board of experts from academia and private institutions, including Cochrane critics, would then agree on what analyses were useful in assessing Tamiflu's public health role.

"We think that would be an appropriate, fair and transparent way of handling this debate," Daniel O'Day said in an interview.

O'Day said complete transparency had to be balanced against the need to protect patient privacy, respect commercial sensitivity and ensure the scientific merit of any statistical analysis.

He stopped short of matching a promise from rival GlaxoSmithKline to make patient-level data from all company-sponsored clinical trials available on a routine basis.

Roche said it had not handed over the full collection of data requested by Cochrane because the group refused to sign a confidentiality agreement.

Cochrane, meanwhile, has accused Roche of stonewalling and urged a boycott of the company's products until it publishes the missing data. Its campaign to force Roche's hand has been backed by the respected British Medical Journal.

EU agency promises openness

The new attempt by Roche to break the deadlock comes as regulators and healthcare experts meet in London to discuss ways to increase transparency over clinical trials.

As Reuters reported in July, the European Medicines Agency (EMA) aims to open its data vaults to systematic scrutiny, after a ruling by the European Ombudsman that keeping data secret is not compatible with the public interest.

Guido Rasi, executive director of the EMA, told the London meeting on Thursday that the question now was "how" to publish clinical trials data not "if" it should be released.

The move puts the EMA ahead of the U.S. Food and Drug Administration (FDA) in terms of data transparency.

The EMA stance is also forcing drug companies to review how far they can keep information they hold on medicines under wraps.

Most companies have committed in recent years to publishing results of clinical trials, either in journals or online, but that openness has not so far extended to the raw data that lies behind those trials.

Britain's GlaxoSmithKline, however, broke ranks last month when it announced that patient-level data from its clinical trials of approved and failed drugs would be made available to other researchers.

Roche's O'Day said his company responded to requests for such data on a case-by-case basis, provided scientists were prepared to sign confidentiality agreements if needed, but this did not mean all data should be released as a matter of course.

"To what level data will be shared proactively and constantly is something we need to discuss," he said.

A Roche spokesman said Cochrane had acknowledged receipt of its proposal for a Tamiflu advisory board but had not given any immediate response.