Members of the British government will be able to abstain from voting on the controversial Human Fertilisation and Embryology Bill, senior Labour MP, Geoff Hoon, announced today.

The bill aims to update the regulation of embryo research and assisted reproduction in light of new attitudes and technological developments. The legislation will allow research using human-animal hybrid embryos, created by inserting animal cells or DNA into early human embryos — a measure that many MPs oppose. These hybrids differ from chimeras — mosaics of cells from different species — which are already used in research at two British universities.

More than 100 scientists, lawyers, philosophers, and theologians wrote a letter to The Times today, urging the government to allow a free vote on the Bill. (The British parliamentary system usually requires that MPs vote along party lines. But under a free vote, MPs can vote however they wish.) Prime Minister Gordon Brown is resisting a free vote for fears that Catholic Labour MPs, including three cabinet ministers, would vote against the bill. He is, however, invoking special "standing orders of the parliamentary Labour party" to allow MPs to refrain from voting, according to The Daily Telegraph. "Nobody will be required to vote against their conscience," said Hoon.

Last month, the government backed down on restrictions proposed in the bill that would have required tissue donors to give explicit consent for use of their cells in embryonic stem cell research. Other contentious issues in the legislation include removing reference to the "need for a father" when providing IVF treatment, and recognizing same-sex couples as legal parents for children conceived by only one of the partners using donated eggs, sperm, or embryos.