In response to a petition from researchers, the UK government has backed down on restrictions to stem cell research proposed in a new bill.

The revision of the Human Fertilisation and Embryology Bill, currently being debated in Parliament, stipulates that tissue donors must give explicit consent for use of their cells in embryonic stem cell research.

But objections from scientists, including a letter signed by about 50 researchers, including four Nobel laureates, and published in The Times on January 21, said that applying that rule to many tissue banks and cell lines in existence would be impossible, because the donors were anonymous. The rule, they argued, would cut them off from conducting stem cell work on key tissue samples, such as older cell lines or disease-specific tissue banks.

Last week, in a letter to members of Parliament who had participated in the debate, the government said it would reconsider the issue. "On balance, the Government has taken the view that the evidence collected is sufficiently strong to justify a limited exception to the requirement to obtain express consent for existing stocks of cells and cell lines."

At the same time, the letter notes, exceptions to the consent rule shouldn't be a mere formality, and will be granted only "where there would be significant adverse impact on scientific research in the public interest, if existing cells could not be used."

A spokeswoman at the Department of Health told The Scientist that it's still unclear how such exceptions should be made. The issue will be debated further in Parliament in the coming weeks.