Cameron will open a public consultation on the issue in March and this has triggered a bout of ecumenism among the Christian churches, with the Church of England and the Roman Catholic hierarchy joining forces to oppose Cameron's plan.

Leading the fray is the second most senior Anglican cleric, Dr John Sentamu, the Archbishop of York, who has warned the Government that it should not overrule "the Bible and tradition by allowing same-sex marriages".

But will the churches prevail in their opposition to the Government? The planned 'consultation' may well show that a majority of the electorate favours allowing gay couples the full entitlements of marriage.

The issue of 'equality' has proved persuasive. And so has the power of example. People now tend to know more gay couples who lead faithful and committed lives together and who are better examples of conjugal loyalty than many heterosexual couples.

So why shouldn't they enjoy the same rights? The argument - by some opposed to gay marriage - that it devalues the institution of marriage doesn't hold water.

The 'progressive' view of marriage is that it is 'just a meaningless piece of paper' and secular liberals have generally disparaged marriage as a patriarchal, bourgeois institution.

The fact the gay lobby is now endorsing marriage as the ultimate commitment has, if anything, reinstated marriage status among trendy thinkers.

The root of this revolution in attitudes is not just about equality, however. The deep change came about with the contraceptive revolution.

Until birth control became accessible, reliable and universally acceptable, marriage was a fertility rite. It wasn't just the Catholic Church that held it was a couple's duty to 'go forth and multiply' - all religions did.

Marriage, universally, was awash with fertility symbols - rice, confetti, orange blossoms, floral posies. Marriage was about creating a dynasty.

Birth control altered all that. When children became a 'choice', rather than a reason for wedlock, the personal relationship replaced the dynastic duty.

If marriage is just about a personal relationship, why shouldn't gay couples have the same benefits as other couples? Many voters will take the modernised view of relationships and yet, the churches will have some support for their opposition.

There is still a deposit of opinion that believes that, while civil unions are fine, marriage still remains 'between one man and one woman'.

Darwinists claim the main purpose of life is biological reproduction. We'll see what emerges.

Certainly, values have been revolutionised since the critic Cyril Connolly wrote in his famous tract Enemies of Promise that the greatest advantage to being a homosexual was that you were free from the trammels of marriage - no in-laws, no boring family constellations and no 'pram in the hall' to impose the worry of raising children.