Seven government ministers, including Ruth Kelly, the transport secretary, and Des Browne, the defence secretary — both Roman Catholics — are expected to join about 200 MPs backing a lower time limit on abortions for non-medical reasons.

Andy Burnham, the culture secretary, is also among those likely to vote in favour of lowering the limit from 24 weeks when it comes before the Commons on Tuesday.

A move down to 22 or 20 weeks’ gestation would be the first change to abortion laws for 18 years.

Nadine Dorries, the Conservative MP leading supporters of a reduction to 20 weeks, said: “People understand now, in a way they never did before, what takes place in a late abortion. They also know what this baby now looks like at this stage.”

Almost the entire shadow cabinet, including David Cameron, the Conservative leader, is expected to back a change. Other senior government backers include Paul Murphy, the Catholic Welsh secretary.

Ministers outside the cabinet who are expected to back a reduction include Liam Byrne, at the Home Office, Tom Harris at the transport department, and Paul Goggins, a Northern Ireland minister.

“Medical science has developed to a point where it is becoming more and more possible for babies born below 24 weeks to survive,” Goggins said. “ When I was health minister in Northern Ireland I saw a small baby in an incubator who was less than 24 weeks old and that was compelling for me.”

Harris added: “I am minded to vote for a lower limit of 20 or 22 weeks for various moral reasons. I am not convinced that, when the 24-week limit was set, that was the right one.”

The vote is expected to be close, with a large number of abstentions. “Pro-choice” politicians, including Emily Thornberry, Labour MP for Islington South & Finsbury, are trying to persuade colleagues to retain the 24-week limit. Regardless of the outcome, abortion will continue to be legal up to birth if the foetus has a disability or the mother’s physical health is at risk.

The debate centres on whether a foetus at 24 weeks is sentient and whether it would have a chance of survival if born at that age. New research shows that up to 65% of babies born at 23 weeks, at which abortion is legal for social reasons, survive in leading hospitals.

In 1990, when abortion laws were last changed, the limit was reduced from 28 to 24 weeks because premature babies born at this gestation survived.

However, a study presented this month by the University of South Alabama Children’s and Women’s hospital found that 70 of the 108 babies born at 23 weeks and admitted to the hospital in 1998-2003 survived. Dr Michael Zayek, the neonatologist who led the study, put this down to medical advances.

Research from University College London hospital, published last year, showed that more than 50% of babies born there at 23 weeks in 1996-2005 survived.

This progress is contradicted, however, by research published in the British Medical Journal this month. A study at 16 hospitals in the Trent region found that a survival rate of just 18% did not improve over 12 years.

A Sunday Times poll has found 59% of women would support a reduction, while 28% back the status quo. Altogether, including men, 48% want a reduction to 20 weeks, while 35% want to retain 24 weeks.

In open letters, religious leaders urged politicians to seize the chance to reduce the 200,000 abortions in Britain every year.

Cardinal Cormac Murphy-O’Connor, leader of the Roman Catholic Church in England and Wales, said this weekend: “There are many people who, in their conscience, feel that there are too many abortions.”

Gordon Brown today challenges religious critics of scientific research using animal-human hybrid embryos, which will also be part of the bill. “We owe it to ourselves and future generations to introduce these measures and give unequivocal backing to stem cell research,” he writes in The Observer.

The survivor

The long campaign to lower the abortion time limit included, in 2005, an address to a parliamentary meeting by Gianna Jessen, 31, a musician from Nashville, Tennessee, who survived a saline abortion in the final three months of her 17-year-old mother’s pregnancy.

Jessen weighed 2lb at birth and doctors said she would never be able to hold up her head or walk. Although she was left with cerebral palsy, she runs marathons to raise money for sufferers. “If abortion is about women’s rights, then what were my rights?” Jessen asked parliament. “If people are going to talk about abortion, then it’s important for them to know these are babies that can be born alive and survive.”

Embryology battleground
As well as the abortion time limits, MPs will also be given free votes this week on the three most contentious proposals in the Human Fertilisation and Embryology Bill.

Hybrid embryos
The bill would legalise the creation of part-human, part-animal embryos. They would only be allowed to live for 14 days and are intended for experiments that scientists hope may lead to treatments for disease.

Saviour siblings
If passed, this provision makes it legal for fertility doctors to screen embryos to choose one that is a tissue match for an existing sibling who has a disease which could be treated with the donation of stem cells, bone marrow or even part of an organ.

Removal of fathers
IVF doctors would no longer need to consider a child’s “need for a father” when offering treatment to single women or lesbian couples.

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