MPs will have the chance to vote tonight on whether the time limit for abortions should be lowered from 24 weeks.

The emotive issue will be debated in the Commons as the Human Fertilisation and Embryology Bill continues its progress through Parliament.

Yesterday they voted, by a majority of 160, in favour of allowing human-animal hybrid embryos to be created to help develop treatments for health problems such as Parkinson's disease, cystic fibrosis and muscular dystrophy.

Today the focus turns to abortion, as MPs debate amendments calling for the time limit for abortions to be cut. The most prominent amendment has been tabled by Nadine Dorries, a Tory MP, calling for the limit to be cut to 20 weeks, but others call for abortions to be banned after 18, 16 and 14 weeks.

Five MPs, including Anne Widdecombe, a Conservative member, want abortions to be banned after 12 weeks.

Supporters of the existing law have signalled their determination to fight the attempted changes, with 86 MPs signing a cross-party Commons motion stating that the current limit was “scientifically and ethically justified”.

Abortion became legal in the UK under the 1967 Abortion Act, which set the limit at 28 weeks because doctors deemed that was the time after which a foetus was viable outside the womb.

In 1990 the limit was lowered to 24 weeks, after advances in the medical treatment of very early babies allowed more to survive at a younger age.

Doctors say that there has been no significant change in their ability to keep very premature babies alive at younger than 24 weeks.

Dawn Primarolo, the Health Minister, said: "There is no science that shows us that the survival rates have changed since we took the decision to have the time limit at 24 weeks."

In 2006, the number of "late" abortions taking place in England and Wales - those between 20 and 24 weeks - was 2,948, about 1.5 per cent of the 193,700 legal abortions that took place that year.

At the other end of the spectrum, 89 per cent of abortions took place at 12 weeks or less.

The reasons for late abortions include risks to the mother's health and severe disability of the developing foetus. Research also suggests that up to 40 per cent of young girls and older women do not realise that they are pregnant for several months, and then agonise for several weeks over whether to terminate the pregnancy.

A majority of women say they should have the right to an abortion at between 20 and 24 weeks of their pregnancy and want the law to stay as it is. A poll of women of childbearing age, conducted by Ipsos MORI on behalf of Marie Stopes International found that 61 per cent say that there should be access to late abortion services for a wide range of circumstances.

When both men and women are asked, however, a majority favour banning abortion earlier. A YouGov poll for the Sunday Times found that only 35 per cent supported the current time limit, and 48 per cent wanted it cut to 20 weeks.

David Cameron today backed a reduction to 22 weeks, though the Conservative leader said that his view was personal and it was a matter of individual conscience for MPs.

“I will certainly vote for 22 weeks, I think this is a really difficult issue, it is another issue of conscience, there is no party whip, Conservatives will be voting in all sorts of different directions,” he told GMTV.

“I think the reason personally why I want to see it come from 24, definitely to 22, is because there are now children surviving, being born at 22, or 23 weeks who survive.

“I think that it is very difficult to have a system that is aborting foetuses at that age when children are surviving. That is my personal view.”

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