Prime Minister Gordon Brown has called for "unequivocal backing" for the measure to help create stem cells to find cures for conditions like Parkinson's an multiple sclerosis.
Scientists say they need to be able to make the hybrids, created by transferring the nucleus of a human cell into an empty animal cell, because of a shortage of donated human eggs.
But some religious groups have condemned the proposal and concerned MPs have submitted an amendment banning the technique.
"They are creating what is ethically quite wrong, something which is animal and human, and that goes against every kind of moral teaching we have ever known," Conservative MP Edward Leigh told the BBC.
Brown has given Labour MPs a free "conscience" vote on this issue and two other measures:
- creating a sibling through IVF to treat a child with a life-threatening condition,
- and the removal of the requirement for doctors to consider the "need for a father" when offering fertility treatment, making it easier for lesbian couples to get IVF.
MPs will also be voting on Tuesday on amendments by pro-life lawmakers to reduce the legal abortion limit to as low as 16 weeks from the current 24 weeks.
Britain is one of the leading states for stem cell research, attracting scientists from around the world with a permissive environment that allows embryo studies within strict guidelines.
The Human Fertilisation and Embryology Authority, which regulates the research, gave permission to two groups of British-based scientists to use hybrids in January.
The House of Lords rejected attempts earlier this year to include a ban on hybrid research in the draft legislation.
