Parliament defeated an amendment to ban inter-species research -- in which human DNA is injected into cells derived from animals -- by 336 to 176 after hours of impassioned debate on ethics versus science.

The vote means Britain retains its status as a world leader in stem cell research. Human-animal embryo research is banned in some countries including Australia, France, Germany and Italy.

Prime Minister Gordon Brown supports the creation of human-animal or "admixed" embryos but some Roman Catholic members of his government oppose the research. Brown allowed members of parliament to vote by conscience rather than on party lines.

"If we want to sustain stem cell research and bring new cures and treatments to millions of people, I believe admixed embryos are necessary," Brown argued in a newspaper article.

The human fertilisation and embryology bill prohibits the transfer of the embryos to a human or animal and says they cannot be used for research beyond 14 days.

The bill, which updates 1990 laws, is at committee stage when amendments are tabled and will be subject to a final vote in coming weeks.

Two groups of scientists have already been given permission to create human-animal admixed embryos. The bill legalises their research within set guidelines.

Some researchers say allowing admixed embryos would open more avenues as they seek cures for conditions like motor neurone disease or Parkinson's. They say their creation would help ease a deficit of donated human eggs for stem cell research.

But other scientists and religious leaders say that creating human-animal embryos is unethical, and using them for research is a blind alley that won't cure disease. One Catholic cardinal called the research "Frankenstein science".

"SAVIOUR SIBLINGS"

David King, director of the campaign group Human Genetics Alert, said he feared sufferers of Alzheimer's and other diseases were being offered false hope.

"It is very sad that all these patient groups have been hyped up to believe in this stuff. They are going to be very disappointed. It is very unfair," he told reporters.

Parliamentarians also defeated an amendment which would have banned the creation of "saviour siblings" -- babies born from embryos selected through in-vitro fertilisation (IVF) because they are a tissue match for a sibling with a genetic condition.

Supporters say this will help children who cannot find matching tissue donors, but critics worry about the impact on children who have been born to improve a sibling's health, particularly if the treatment fails.

The embryology debate will continue on Tuesday when members of parliament will vote on moves to end the need for IVF clinics to consider a child's need for a father.

This would ease restrictions on lesbian couples and single women but opponents argue that a child needs a father.

Parliament will also vote on Tuesday on abortion laws. Some MPs are seeking to lower the 24-week time limit for abortions. Brown favours the status quo.