Tony Blair's former science adviser today warns the government that new legislation on human tissue could cut off "vital avenues of research" and hamper the understanding of disease.

Lord May, speaking as president of the Royal Society, Britain's leading scientific academy, was for five years the government's chief scientific adviser. He and many others want to see urgent changes in the human tissue bill soon to come to the House of Lords.

The bill was drafted as a response to the scandals at Bristol royal infirmary and Alder Hey hospital in Liverpool, when children's organs were kept for research without parental consent. But many scientists believe that the legislation, even after many changes, could impose too much paperwork and smother important research.

"The scientific and medical communities have been making their concerns known since the start of this bill but the Department of Health appears to be carrying on regardless," Lord May said. "The government must take action to ensure that these concerns are fully addressed."

He said the Royal Society wholeheartedly supported the aim of the bill, which was to increase public confidence in the collection and use of human tissue and organs. But the government was oversimplifying the issue and making the need for consent too broad.

"It's like using a sledgehammer to crack a nut," he said. "No distinction is made between tissue samples taken during routine diagnostic tests at one end of the scale and the removal of organs during post-mortem at the other.

"The prohibitive amount of bureaucracy that could be generated by the need to obtain consent for individual tissue samples would impact on teaching and lead to reduced levels of vital research into understanding diseases such as cancer, heart disease, Parkinson's and vCJD."

Since the birth of modern medicine, lecturers, students and researchers have depended on a supply of human tissue, for anatomy lessons, to study the action of an infection, and to test new treatments on cell cultures. Almost all biomedical breakthroughs have depended at some point on a close study of samples of human flesh and blood, preserved in laboratory collections.

Researchers need to be able to use samples again and again, to understand disease, to find new treatments, to launch investigations when research goes wrong and to open up avenues of study as medical technology advances.

Collections built up in British hospitals and laboratories so far will be exempted from the bill, but the government has promised that a human tissue authority will devise codes of practice for handling these, too. Lord May said this guidance could impose restrictions without any scrutiny by parliament. Researchers would have no chance to comment.

"It would be impractical and impossible to predict in advance all of the possible research uses for samples, as required under the current bill. The definition of consent needs to allow for the fact that the scope of research programmes inevitably changes over time."