Scientists could be breaking the law if they implement parts of the new Human Fertilisation and Embryology Act, an academic has claimed.
David Jones, a Roman Catholic who is opposed to embryo research, believes existing legislation may nullify clauses that permit researchers to use human tissue without the donor's direct consent.
The Act, which allows human-animal hybrid embryos to be created for stem-cell research, was passed last week. Research provisions will come into force in October 2009.
At issue are so-called presumed and substitute consent clauses, which were added late in the Bill's passage through Parliament.
These allow researchers to "presume" that consent has been given for genetic material such as skin or blood to be used to create human and human-animal hybrid embryos.
As a result, tissue can be taken from people who lack the mental capacity to give consent if relatives, carers or, in their absence, a person nominated by researchers agrees.
It can also be taken from seriously ill children whose parents give permission, or anyone who has already donated samples for medical research but who cannot be contacted.
However, according to Professor Jones, who is director of the Centre for Bioethics and Emerging Technologies at St Mary's University College, these clauses may contravene human rights laws.
Having sought advice on the issue, he is urging researchers not to rely on presumed consent, warning that they could be open to legal challenge on the grounds that what happens to individuals' cells is a private matter covered by the Human Rights Act.
He said that institutions and ethics committees should be "ultra cautious" about how they proceed, pointing out that the Government's own lawyers had initially thought that the clauses would be illegal but changed their minds after "heavy scientific lobbying".
The presumed consent clauses are now justified by the Government as being of "scientific necessity", which Professor Jones said "shows how open to challenge the legislation is".
Among those who could mount challenges, he said, are donors who have given genetic material to tissue banks in the past but who can no longer be contacted.
"I am sure that when people give general consent to use tissue samples they don't think that they are going to be used to create human embryos," he said.
Professor Jones has raised the issue as debate continues to rage over whether the law should be changed to allow presumed consent for organ donation.
He said: "The irony is that the most controversial research that is going on in the country is the one they have chosen to have presumed consent in."
He also warned that there could be commercial implications if the UK finds it hard to sell embryo-derived stem-cell lines abroad because of consent issues.
While the UK is loosening its rules in this area, the US and other countries are seeking to tighten them. "That means consequences if we are trying to sell bioproducts," he said.
Despite Professor Jones' concerns, Stephen Minger, director of the stem-cell biology laboratory at King's College London, defended the addition of the clauses.
He said that the number of situations where consent would be presumed was likely to be "very small", that access to rare material that could be important for research might be lost if the clauses had not been included, and that appropriate safeguards were in place.
"You can't use (a person's material) if you are aware you would in some way be violating their personal beliefs about how their cells should be used," he said.
In the case of those who lacked "mental capacity" and for children, he said he saw no difference between the new arrangements and those already in place for other medical procedures where people could not give consent themselves.
In the case of material in tissue banks, he stressed that consent for research had already been given, but the issue was that the consent was "wide rather than specific".
He also denied that commercial problems would arise, arguing that having the clauses in primary legislation actually made the UK's consent rules clearer.
James Lawford Davies, a lawyer at Clifford Chance and a lecturer at Newcastle University, has been involved in the debate surrounding the new legislation.
He said the area was complex and the legislation would be difficult to challenge, but if it was it would probably fall to the Government to defend it rather than researchers or universities.
A Department of Health spokesman said: "The provisions in the Bill were referred to the Joint Committee on Human Rights for consideration. The committee raised no concerns."
Rory Collins, head of the Government-funded Biobank project, which currently stores samples from nearly 220,000 people for use in research, said that although participants were not specifically asked whether their material could be used for embryo research when they signed consent forms, contact was maintained with all participants so they could be asked if necessary.
He said that Biobank would need to take an overall decision about whether the samples could be used for embryo research.
"It might be felt that it was not an appropriate use," he said.