British lawmakers voted against a bid to ban the creation of animal-human embryos for medical research on Monday, despite critics including the Catholic Church charging the move was unethical.

The House of Commons was voting on the Human Embryology and Fertilisation Bill, potentially the biggest shake-up of laws affecting sensitive areas like stem cell research and abortion for nearly two decades.

An amendment to outlaw the creation of human-animal hybrid embryos, which can ensure a more plentiful supply of stem cells for use in research into treating conditions like Alzheimer's and Parkinson's, was defeated by 336 to 176 votes.

Lawmakers also voted against a bid to ban "saviour siblings" — children created as a close genetic match for a sick brother or sister so their genetic material can help treat them — by 342 to 163 votes.

Prime Minister Gordon Brown, who wrote an impassioned defence of both measures in a newspaper on Sunday, and David Cameron, leader of the main opposition Conservatives, were among those opposed to the proposed embryo ban.

Brown's youngest son Fraser, aged nearly two, has cystic fibrosis, a disease which could one day benefit from embryo research.

"I believe that we owe it to ourselves and future generations to introduce these measures and in particular to give our unequivocal backing, within the right framework of rules and standards, to stem cell research," Brown wrote in the Observer.

Lawmakers had a free vote on sensitive parts of the bill, being debated and voted on in the House of Commons Monday and Tuesday, meaning their parties will not whip or take a line on it and they can follow their consciences.

Three Catholic members of Brown's Cabinet, including Defence Secretary Des Browne, supported a ban on hybrid embryos.

A 'hideous' concept

The Catholic Church is fiercely opposed to the bill — in March, the Catholic leader in Scotland, Cardinal Keith O'Brien, called the concept of animal-human embryos "hideous".

"It is difficult to imagine a single piece of legislation which more comprehensively attacks the sanctity and dignity of human life than this particular bill," he said in an Easter Sunday sermon.

Edward Leigh, the Conservative lawmaker who tabled the amendment proposing the hybrid embryo ban, argued in the House of Commons that hybrid embryos were "ethically wrong and almost certainly medically useless".

And his colleague David Burrowes, who led calls for a ban on "saviour siblings", said that no child should be "deliberately created to be used for the benefit of another, no matter how pressing the need".

But the chief executive of the Medical Research Council, Sir Leszek Borysiewicz, said the vote would help keep Britain at the forefront of research in the field.

"It (the bill) brings the right balance of opportunities to make headway to find cures for some of the most pernicious diseases (...) whilst ensuring that appropriate safeguards are in place through the law and the regulator," he said.

Hybrid embryos are created by inserting the nuclei of a human cell into an animal egg and can ensure a more plentiful supply of stem cells.

AFP