Doctors want more people to request autopsies for their dead relatives as the number of postmortem examinations drops to an all-time low.

Sir James Underwood, president of Royal College of Pathologists, said yesterday that research into how certain diseases kill people is suffering. He made the comments at the launch of a new human tissue bank at the Western General hospital in Edinburgh, which opened for business today with a £300,000 grant from the Medical Research Council. It will be the world's first facility to collect healthy as well as diseased organs during autopsies for further study by researchers.

"The examination of the body after death has contributed enormously to our knowledge and understanding of disease," said Prof Underwood. "Within the last decade, it has led to the discovery and characterisation of variant CJD."

But autopsies have fallen from 50% of deaths in British hospitals in the 1960s to less than than 5% today. In the wider community, only a quarter of deaths are subject to postmortems, and the majority of those are due to coroners' requirements. The professor wants more people to consider asking for autopsies on relatives, if only to confirm cause of death.

"Up to 30% of certified causes of death are significantly wrong or incomplete," said Prof Underwood. "In 2003, a postmortem study in Birmingham showed that major misdiagnoses were present in almost 40% of deaths in an intensive care unit. Conditions such as heart attacks, cancer and pulmonary embolism were most frequently missed diagnoses."

He blamed the decline on the "ill-founded belief" that modern medicine always yields the right causes of disease.

A recent audit in Sheffield revealed that relatives were likely to allow autopsies in 50% of cases if the need for research was justified to them. But few were given the opportunity to consider consent.

"They are never told that the cause of death on the certificate is, in a sense, the best guess and only a postmortem can fully and reliably reveal why their loved one died," said Prof Underwood. "Nor are the relatives advised, sensitively of course, that postmortems provide opportunities for altruism."

Part of this altruism would be to donate tissue to banks such as the Edinburgh facility.

Another reason for the fall in requested autopsies is recent unease after the organ retention scandals at hospitals such as Alder Hey in Liverpool.

Next year's Human Tissue Act places strict conditions on what tissue can be used.