David Cameron put his credentials as a modernising politician at risk last night by voting for a cut in the abortion time limit to 20 weeks.

He also voted against a measure that makes it easier for lesbian couples to receive IVF treatment.

The move suggests traditional family values will play a much greater role in the Conservatives’ general election campaign than previously thought.

Colleagues said he chose to side with the right wing of his party because the issue of absent fathers goes to the heart of his message that Britain’s society is broken.

Gordon Brown and most Labour MPs backed the status quo on abortion. That contributed to a larger than expected majority in favour of keeping the limit at 24 weeks.

A so-called “compromise” amendment calling for the limit to be lowered to 22 weeks proposed by a pro-choice Tory MP failed to get as much support as anticipated.

Pro-choice campaigners welcomed the outcome and said they will now set their sights on other moves to liberalise the current law. In particular, they want to see a move towards “abortion on demand” where women do not have to gain the consent of two doctors.

They also want abortions to be offered away from hospitals and special clinics.

“Tonight’s vote to retain the 24-week time limit spells relief for women across the country,” said Anne Quesney, head of advocacy at Marie Stopes International.

“Having secured this victory for common sense, compassion towards women’s needs and sound medical science, it’s now time to look forward to the next stage of the Human Fertilisation and Embryology Bill. We expect to see progressive amendments introduced that will improve current legislation, not least the removal of the archaic requirement for two doctors to give permission before any abortion may be performed.”

But pro-life campaigners will be comforted by Mr Cameron’s decision to support a cut in the time limit of one month.

Speaking before the vote yesterday, the Conservative leader said he was swayed by the thought that some babies could survive at a younger age than 24 weeks.

“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. It is very difficult to have a system that is aborting foetuses at that age when children are surviving.”

But Mr Brown said science was a reason to back the existing law, but added that his religion guided the way he voted. “I respect all the views that people have on this matter. Some are religious. I hold from my own religious views that this is the right decision for Parliament to continue to make. The medical evidence has not changed and I will support 24 weeks,” he said.

A hard core of fewer than 100 MPs voted for drastic reductions to the time limit to 12 and 16 weeks. They included three Cabinet members: the Defence Secretary, Des Browne, the Transport Secretary, Ruth Kelly and the Welsh Secretary, Paul Murphy.

In a highly charged debate, many MPs spoke of their personal experience.

Nadine Dorries, a Conservative MP for Mid Bedfordshire and a former nurse who proposed a reduction in the limit to 20 weeks, said she had witnessed a “botched” termination while working on a ward.

In a graphic illustration of her case, she said: “A little boy was aborted into a cardboard bed pan which was thrust into my arms. As I stood and looked in that cardboard bed pan this little boy was gasping, through mucous and amniotic fluid, for his breath and I stood with him in a sluice, in my arms in a bed pan, for seven minutes while he gasped for his breath and a botched abortion, which became a live birth, became a death seven minutes later.”

Judy Mallaber, Labour MP for Amber Valley, raised the spectre of the return of back-street abortions, where women were prepared to risk their lives to end a pregnancy.

“All too often the woman is left out of this discussion — she becomes invisible — and women have different moral views on whether abortion is acceptable and if so the circumstances in which it is acceptable,” she said.

Mike Penning, Tory MP for Hemel Hempstead, told MPs that when he had had a vasectomy on the NHS he had had a cooling-off period so he could reflect on the decision before going ahead. A similar “cooling-off period” should be compulsory before an abortion.

Dawn Primarolo, the Health Minister, addressed the emotive issue of whether the disability of the child should be grounds for abortion.

“Is it right to force a woman to carry a child (with a serious handicap) until it dies in the womb or is born with no chance of survival?” she asked.

In the debate about a father’s role the former Conservative leader Ian Duncan Smith said that removing the stipulation that the role of a father was considered would amount to telling couples seeking fertility treatment that “fathers are not important, or are less important than mothers”.

While it might cause lesbian couples unease it was not discriminatory, he said.

He was backed by a number of Labour MPs: one, David Taylor, said it was perverse to write the father out of the script. Another, Geraldine Smith, said: “We are not insisting that any single woman or lesbians do not have IVF treatment; the only thing we are saying is that there should be some father figure somewhere — it may be a grandfather, it may be a relative.”

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