A law drafted in the wake of the Alder Hey organ scandal could blight legitimate research projects, say leading scientists.
The tiniest samples will require consent for research
The Human Tissue Bill - which is close to becoming law - is to prevent organs being taken without relatives' consent.
But scientists say the changes go too far and will make teaching and medical research extremely difficult.
There is no discrimination between whole organs and a collection of a few cells on a microscope slide, they say.
Cancer charities and the Wellcome Trust are calling on ministers to make changes to the Bill.
But ministers deny that vital research will be affected, saying the law "builds on existing best practice".
The Bill makes taking any kind of human tissue without consent an offence, as would selling human bodies or body parts, or storing them without a licence from a new regulatory body.
At Alder Hey, and dozens of other hospitals around the country, it was standard practice to remove for analysis - or simply for research purposes - organs from both adults and children who died in hospital.
Checks at many hospitals revealed archives of tissue samples and organs, many of which had been taken without the knowledge or consent of relatives.
The new law states that using any tissue sample, no matter how small, for research, is illegal unless written consent has been obtained from the patient themselves or a relative.
If research institutions want to test, for example, blood samples to check the prevalence of a virus in the general population, they have to make sure that for every sample, they have a form signed by the patient consenting to its use in this way.
Dr Mark Walport, director of the Wellcome Trust, which spends more than £400 million on medical research each year, says this creates an impossible situation for mainstream researchers.
"We agree there should be legislation to ensure there is proper permission for organs taken during post mortems.
"But we do not believe the same requirements should apply to blood samples or pieces of tissue removed during surgery which are then used, anonymously, for research."
He is calling for the parts of the Bill dealing with tissue samples taken from living patients to be delayed for further consideration.
He gave examples of "breakthrough" research carried out in the past which would be impossible under the terms of the new law.
These included the discovery that asbestos was the cause of a cancer called mesiothelioma - and research which checked large numbers of blood samples for the presence of the newly-emerged Aids virus.
Professor Peter Furness, a pathologist from the University of Leicester, said that more than three million samples were taken annually from living patients - and more than 100 million blood samples.
Getting consent from all of these people would be the responsibility of hard-pressed doctors, he said - but it would be the pathologist down in the lab who would face criminal charges if consent was not taken properly.
He said: "The threat of this Draconian sanction will make people cautious.
"It's not what the Act says - it's what people think the Act says that matters."
Dr Richard Sullivan, from Cancer Research UK, said that the type of research which had contributed to a trebling of survival in childhood cancer since the 1960s was now threatened, along with research into other types of cancer.
He said: "Between 5% and 8% of research uses post-mortem samples.
"Without access to these, we wouldn't know, for example, how many men are carrying 'silent' prostate cancers."
He described the law as "complex, obfuscatory and contradictory".
However, Health minister Rosie Winterton denied that the Bill was out of step with the needs of researchers.
She pointed out that the legislation had earned the support of the General Medical Council - the body which regulates doctors, as well as patient groups.
She said: "It will provide certainty and confidence for the public, patients and their families, doctors and researchers - to ensure that the donation of organs and tissue for valuable medical research is supported by a clear framework of consent.
"It is not retrospective and need not be onerous as it simply builds on existing best practice.
"Science and research will flourish only if we proceed with the support of patients and society in this way."