By Robert Pigott
Religious affairs correspondent, BBC News
Protesters marked the 40th anniversary of the Abortion Act
Forty years after the Abortion Act came into effect, terminations in Britain are running at 450 a day.
Opponents of the legislation say the scale of abortion is reason enough to introduce substantial restrictions.
But as the issue seems about to become more political, pro-choice activists say the law should actually be relaxed.
A coalition of anti-abortion campaigners gathered outside Parliament to focus attention on what they say is the toll taken by the Abortion Act.
Since 1967 the yearly rate of abortion has multiplied - from 22,000 in 1968 to 193,000 last year. More than a fifth of pregnancies end that way.
The Act was intended to protect the health of desperate women who might otherwise seek the help of back-street amateurs.
Now, even Lord Steel, who, as a backbench MP, put forward the legislation, accepts that abortion has become a form of contraception.
Rarely has there been so much at stake in the debate about abortion.
A Human Fertilisation
and Embryos Bill is expected shortly to be introduced into Parliament. It is likely to give both sides an opportunity to table amendments changing the law on abortion.
That fact alone has led to a significant rise in the tension, visible among those brandishing placards on the streets of Westminster.
Among them was 17-year-old Antoinette Akoiye, at the rally with a smiling woman in a wheelchair.
Ms Akoiye said her mother was advised to have an abortion.
"I'm very happy and very fortunate enough that she took a stand but not many mothers can. They just go along with the doctor's advice and" - she makes a gesture with her hand - "gone."
Abortion law has been changed before.
In 1988 the upper limit for aborting a foetus was reduced from 28 weeks' gestation to 24 weeks.
In the battle to reduce it further, anti-abortion groups are publicising progressively clearer images of foetuses down to 12 or so weeks of gestation, drawing attention to their already human appearance.
But now pro-choice groups see an opportunity to press for a relaxation of the law - partly in the belief that MPs who oppose abortion are outnumbered by those who support a woman's right to choose.
John Parsons, a consultant gynaecologist who has been performing abortions for decades, wants new legislation to give young women, in particular, easier access to abortion.
"I actually believe that there aren't enough abortions," said Mr Parsons.
"I believe that there aren't enough people who realise that this is a sensible option. I am very concerned about the young girls, teenaged women having babies. That's really not sensible."
Mr Parsons would like to end the rule requiring two doctors to sanction abortions and to allow nurses and others to perform them.
He said women should be able to get drugs over the chemist's counter to allow them to abort foetuses up to nine weeks in gestation at home.
He said the effect would be something like "the worst of periods".
For Mr Parsons, improved sex education was the best way to bring down the number of abortions.
"There are too many unintended pregnancies and we should be improving the contraception facilities availability for young people."
The Roman Catholic Church - for which abortion is nothing less than the killing of a human being - is reluctant to sanction contraception as a weapon in the battle to reduce the rate of abortion.
But its approach to the 40th anniversary of the Act has been marked by a new realism, in particular an acceptance that a complete ban may not be "achievable".
In May, a powerful attack by the head of the Scottish Catholic Church Cardinal Keith O'Brien against Catholic politicians who support abortion, left an impression of inflexibility on a matter of absolute principle.
Last week, however, Cardinal O'Brien and the leader of the Roman Catholic Church in England and Wales, Cardinal Cormac Murphy-O'Connor, wrote a joint open letter which called for a campaign that accepted "incremental" changes in the law.
In effect it gave Catholics permission to vote for abortions after 20 weeks' gestation, if the only option was a less restrictive limit of 24 weeks.
"We're trying to change minds and hearts - that's what this rally is about," said Cardinal Murphy-O'Connor as the protesters walked from the Houses of Parliament to service in Westminster Cathedral for a service designed, they said, to commemorate the 6.7 million foetuses aborted since 1967.
"But it's legitimate for politicians to support incremental change," he added.
"While they may be - and hopefully are - totally opposed to abortion, at the same time if they feel this is an achievable aim to lessen the limit, then that's something I would support."