Drug companies and medical researchers are putting patients' lives in danger by failing to publish unfavourable results from clinical trials, MPs have warned.

The lack of transparency means many trials are not registered before they are done, while results are held as private documents that cannot be scrutinised by patients or independent experts.

The practice skews the information that is available to doctors because trials that show new experimental drugs in the best light are more likely to be published, and results that could prevent harm or save patients lives may never see the light of day. Often, trials that indicate a new treatment is not effective are never published.

In a report delivered to ministers, MPs express dismay at the government's efforts to tackle the problem and set out concrete proposals to make data from clinical trials more openly available.

"Many of the trials taking place today are unregistered and unpublished, meaning the information that they generate remains invisible to both the scientific community and the public. This is unacceptable, undermining public trust, slowing the pace of medical advancement and potentially putting patients at risk," said Andrew Miller, chair of the Commons science and technology committee.

The MPs' report broadens the traditional battleground over clinical trials data to include academic researchers who fail to publish studies of companies' drugs or other medical interventions.

The pharmaceutical industry is under intense pressure to release more clinical trial data, and some companies, such as GSK, are already committed to greater openness. But the MPs call for government action to speed the process, by requiring all future trials to be registered, and summaries of trial results to be made public. More detailed "clinical study reports" should also be released, with redactions to protect patient privacy, when they have already been prepared for regulators.

In another recommendation, the MPs urge the government to demand the registration of past trials too, with summary results released for all publicly funded trials since 2000.

Failure to release clinical trials data has led to hefty fines for some pharmaceutical companies. In 2004, GSK paid $2.5m to settle a consumer fraud case during which it emerged that the company had lied about the safety and effectiveness of its antidepressant Paxil, also known as Seroxat.

But academics are also guilty of suppressing data that could have helped patients. In 2006, six volunteers suffered severe reactions to an experimental drug called TGN1412 in a trial at Northwick Park hospital in London. An inquiry into the incident found that a single patient had suffered the same catastrophic reaction after taking a similar drug, but the scientists had never reported the findings.

Scientists estimate that half of all clinical trials that have been completed have never been published in academic journals, and trials with favourable results are twice as likely to be published as others.

"There have been these examples of publication bias which have resulted in lots of people suffering and dying unnecessarily, which somehow people haven't taken seriously," said Iain Chalmers, co-ordinator of the James Lind Initiative at Oxford University, which lobbies for better trials.

"I don't blame the drug companies. The drug companies will get away with whatever they can get away with within the law to look after the interests of their shareholders. But they couldn't get away with these things were it not for members of my profession being willing to collude with them and put patients in second place.

"Quite apart from the risks posed to patients of hiding the results of research, it's completely ridiculous that people think discovering useful drugs is going to be efficient if you bury half or more of the stuff that you find. It's ludicrous that people think that UK Plc's best interests are served by handicapping the scientific process in this way," he added.

From the end of September, the Health Research Authority will require trials to be registered before they can receive approval from an ethics committee.

Dr Carl Heneghan, director of the Centre for Evidence-Based Medicine at Oxford University, said more openness was essential for the development of better healthcare and medicines in the future.

"We need to learn about the effective medicines and the ineffective medicines more efficiently. We need to know about all of them," he said. "There's an important principle in science, that it's built on replication. If I do an analysis, I must show the data that analysis is based on. In the modern world, we're not going to stand for this lack of transparency."

The report goes on to criticise the excessive bureaucracy that must be navigated to run a clinical trial in the UK. The Health Research Authority was created to make it easier for companies, but MPs said it was impossible to judge if the HRA was proving successful, and were concerned to find that many in the industry were only "dimly aware" of the body and its intended role.

Sara Osborne, Cancer Research UK's head of policy, said; "Information from clinical trials should be published as soon as the results are shown to be reliable. This is vital for both patients and researchers.