Cameron: Time limit on abortion should be lower than 24 weeks

The Conservative leader will vote to lower the deadline for terminations, possibly to as early as 20 weeks.

Pro-life MPs are seeking to engineer a vote on abortion during debates on the Human Fertilisation and Embryology Bill in the next few weeks.

Mr Cameron said: "I would like to see a reduction in the current limit, as it is clear that, due to medical advancement, many babies are surviving at 24 weeks.

"If there is an opportunity... I will be voting to bring this limit down from 24 weeks. This must, however, remain a conscience issue and a free vote."

A majority of MPs on the Commons science and technology committee rejected lowering the abortion time limit in a report published last year.

However, Mr Cameron's intervention is hugely significant as, unlike in America, political leaders have tended not to take a lead on this issue.

The Tory leader is understood to have been swayed by technological breakthroughs including 3D pictures showing foetuses seemingly "walking in the womb" at 12 weeks and is waiting to see what amendments are tabled to the Bill before deciding what lower time limit to support.

Ministers, though, have so far refused to review the abortion laws despite growing demands from religious leaders and MPs, many of whom believe terminations are being used as a form of contraception.

Nadine Dorries, the Tory MP for Mid-Bedfordshire who was formerly a nurse, said: "With the factual evidence we have, there can be no reason why any MP could, with all conscience, agree to the 24-week limit.

"It's not an issue of women's rights or pro-life. The question is are we a decent and humane society or aren't we?"

But Tony Kerridge, of Marie Stopes International, the biggest provider of terminations outside the NHS, strongly defended the status quo.

He said: "David Cameron's views fly in the face of the medical establishment, which has concluded there is not yet enough scientific evidence to bring down the legal abortion limit."

Stressing that just one per cent of mothers in Britain have an abortion at the 20 to 21-week point, he added: "This extreme minority is commonly made up of very young mothers with very compelling reasons to opt for a late termination.

"We believe these young women should be supported, not vilified for their difficult choices."

More than 200,000 abortions are now being carried out a year.