The government has survived two big challenges to its controversial plans to change the law on embryo research for the first time in 20 years.
A cross-party attempt to ban hybrid human animal embryos was defeated on a free vote, by 336 to 176.
Catholic cabinet ministers Ruth Kelly, Des Browne and Paul Murphy voted for a ban. PM Gordon Brown and Tory leader David Cameron both opposed it.
A bid to ban "saviour siblings" was voted down by 342 votes to 163.
The votes followed two impassioned debates in the committee stage of the Human Fertilisation and Embryology Bill, aimed at updating laws from 1990 in line with scientific advances.
On Tuesday, MPs have a further free vote on the emotive issue of cutting the abortion time limit.
Mr Cameron, along with Mr Brown, has backed the use of hybrid embryos as a means to develop treatments for cancer and conditions such as Parkinson's and Alzheimer's disease. They also both support the creation of "saviour siblings".
However, the majority of the Tory shadow cabinet, including shadow foreign secretary William Hague and shadow home secretary David Davis, backed the unsuccessful attempt to ban hybrids.
Ex-minister Edward Leigh, who led the fight against the creation of hybrid "admixed" embryos, said they were "ethically wrong and almost certainly medically useless".
He said there was "no evidence yet to substantiate" claims the work could lead to treatment for degenerative diseases like Parkinson's and Alzheimer's.
The bill would allow regulated research using hybrid or "admix" embryos, where the nuclei of human cells are inserted into animal eggs. The resulting embryos would be kept for up to 14 days to harvest stem cells.
Health Minister Dawn Primarolo says any research done using human embryos "must satisfy the Human Fertilisation and Embryology Authority that it was necessary or desirable".
No human "admix" embryo would be implanted into a woman or animal, she says.
But Mr Leigh said: "We do not believe that regulation is enough. We believe this is a step too far and therefore should be banned.
How hybrid embryos might be created
And ex-Labour minister Sir Gerald Kaufman, agreed, adding: "How far do you go? Where do you stop? What are the limits and what are the boundaries?
"If you permit the creation of hybrid embryos now, what will you seek to permit next time, even if you have no idea where it will lead?"
Labour's Chris Bryant, a former Anglican curate, said Mr Leigh's arguments were like those used by church leaders against the smallpox vaccine.
"They were wrong and I think you are wrong today," he said.
Liberal Democrat Evan Harris criticised those who argued hybrid embryos were too human.
"If it's ethically acceptable to use up and destroy fully human embryos with all the potential they have, how is it right to provide for hybrid embryos, with less potential of viability, greater protection?" he said.
A separate attempt to ban "pure" hybrid embryos, that would mix a human egg with animal sperm or vice versa, was also defeated in the Commons by 286 votes to 223, a government majority of 63.
Tory David Burrowes' attempt to stop parents having so-called "saviour siblings" - babies selected to provide genetic material for seriously ill relatives - also suffered defeat.
The Bill would allow the selection of embryos that are a tissue match for a sick older brother or sister.
But Mr Burrowes said it was wrong to create a child for the benefit of another, regardless of "the need".
MPs are being given a free vote on four controversial parts of the bill. The other two areas are:
The Roman Catholic Church has branded the use of hybrid embryos as "monstrous" and says tinkering with life in this way is immoral.
Catholic bishops in Britain and the Irish Republic have given £25,000 to scientists using adult stem cells, which is less controversial than using immature ones.
Such cells can be used to create brain, skin, heart and other tissue for treating diseases.
But Sir Leszek Borysiewicz, chief executive of the Medical Research Council, said the result would keep the UK at the forefront of embryo research.
Conservative leader David Cameron, along with Mr Brown, has backed the use of hybrid embryos as a means to develop treatments for cancer and conditions such as Parkinson's and Alzheimer's disease. They also both support the creation of "saviour siblings".
Scientists at Newcastle University announced last month that they had created the first part-human, part-animal hybrid embryos in the UK.
They were created by injecting DNA derived from human skin cells into eggs taken from cows' ovaries which had had virtually all their genetic material removed.
Researchers say these human-animal "admixed" embryos could help solve the current problem of the lack of human eggs from which to generate embryos.
Return to story