We are blasé about abortion in Britain; opposition to it is as muted as is the support for it (which is why we are running out of doctors prepared to carry it out). It is merely an unexceptionable part of the fabric of society.

Contrast us with the United States, where the issue splits the nation, and each side gives itself a powerful, emotive label: one is Pro-Choice, the other is Pro-Life. Early termination has an infinitely greater social, religious and indeed political resonance In the Land of the Free than it does here.

Why? The reasons go the heart of our differences as countries. For Americans, the issue encapsulates a major fault line in their society: the one that opened up in the 1960s, between freedom and authority. On one side is the heady freedom from age-old social constraints that the Sixties brought in - especially sexual freedom, and in particular, sexual freedom for women. America was the birthplace of modern feminism, and one of feminism's central tenets is a woman's right to choose what she does with her body. The contraceptive pill, and legalised abortion, were the means to this end.

But on the other side of the divide is the old attitude that has never accepted abortion as a woman's right, or as a justified act. And what lies behind this, and keeps it alive, is religion.

Many British people probably have no concept of just how religious American society is, and how distinct that makes Americans from us. We speak the same language, eat the same food, take part in the same wars; but on Sundays, we do things differently. According to Gallup, 98 per cent of Americans believe in God, and 73 per cent believe in life after death (compared to 38 per cent in Britain); even more strikingly, 40 per cent are regular churchgoers. Every Sunday, 120 million Americans make the effort to worship in Christian churches, the wealthy, the middle-class, the poor.

That is not to say, of course, that the Catholic church has not tried to stem the tide of pro-choice legislation in Britain. Last year it threw its weight behind efforts to pressure the government into changing abortion laws, claiming that public opinion had shifted after ultrasound images were published showing striking details of foetuses seeming to "walk" in the womb. Cardinal Cormac Murphy- O'Connor, leader of the church in England and Wales, lobbied the Health Secretary, Patricia Hewitt, for a review of laws which set the limit for termination at 24 weeks. "What has happened is that there has been a quite considerable change in public opinion, especially after those photographs," he said. "That has touched a lot of people's hearts."

Although the attempts to cut the age limit came to nothing he may, in light of the looming abortion crisis, have had a point, though not quite the one he intended. There does seem to have been a gradual, almost imperceptible change in public opinion - not because so many people have been converted to the pro-life cause, but because many seem to have taken the pro-choice cause for granted.

Complacency can kill off any campaign, however passionately it is taken up. No doubt the women who fought with such fervour to achieve the 1967 Abortion Act and those who continued the battle through the Seventies and Eighties until the word "termination" lost much of its stigma would be aghast at the way in which their hard-won gains have been squandered.

What do we fight our battles over in 21st century Britain? Only the extreme end of the animal rights movement seem to involve such a strong element of passion. Many Americans looked on bewildered at the amount of time and energy spent on banning foxhunting in Britain, just as we look on assassinations of American abortion doctors as something entirely outside our experience.

There's the difference between us. America is a society based on religion, where half the nation has not accepted legalised abortion. Ever since the historic Supreme Court decision of Roe versus Wade made abortion (up to three months) a constitutional right in 1973, much of this vast body of religious opinion has fought back, firmly believing that killing a living human foetus is prohibited by God. Sometimes the fight has been violent, and gone beyond demonstrations outside clinics; the phenomenon of "Pro-Life murder" has seen several abortion doctors and clinic workers killed by gunmen or bombers.

We in Britain, meanwhile, have lost our religion, and acquiesce entirely placidly in all the liberations of the Sixties and Seventies, although as a society based on class, many of us can still get very worked up at the prospect of a toff on a horse.