Years ago, I used to urge my students at Oxford to conduct their love affairs in silence. I told them that the laws that govern property ownership might depend on the way in which the title of their home is registered, but also on what is said in a relationship. So if those young men said to a woman: "Come and live with me and I will take care of you ? you don't need your own place", they might have found that they were in debt to the tune of half the property when love came to an end. At least my students knew the pitfalls.

Cohabitation is gradually gaining more recognition in English law and without much debate. Recently, special laws for cohabitants, which would treat them like married couples on separation or death, have been proposed by the Law Commission and, in a private bill, by the Liberal Democrat peer Lord Lester. This is dangerous. Despite the no doubt good intentions, cohabitation law retards the emancipation of women, degrades relationships, takes away choice and would extend an already unsatisfactory maintenance law for married couples to another group. Women do not need and ought not to require to be kept by men (and vice versa) after their relationship has come to an end. Instead, we should all have the right to live together without having a legal structure imposed without our consent or contract to that effect.

Fourteen per cent of British couples are cohabitants (with 1,250,000 children). The median duration of the cohabiting relationship is two years, after which they marry or separate. Cohabitation is made less stable by childbearing, according to the statistics, as more of the couples without children stay together. Seventy-five per cent of those in such relationships hope to marry. Imagine how cruel it would be if a new law meant a young, successful career woman had to pay out to the man who would not marry her and left her.

The main argument in favour of a special law is the need to support children of cohabitants. But the 1989 Children Act already provides that a parent of a child may apply to court for the other parent to support the child and the carer parent by property or maintenance. This takes care of the argument that cohabitants must be responsible for their children; that law could be widened if necessary, without trespassing on the principle that I espouse, the freedom of cohabitants to live outside the law while being responsible for their children.

The best thing for children, as the statistics show, is to live with two married parents. The construction of a forced law of cohabitation may deter more men from making any commitment, let alone marriage. We ought not to risk adding to the number of one-parent families by tempting men to walk out before the threshold qualifying period, say two years, in order to avoid financial liability, when all recent studies show that Britain's children are the unhappiest and poorest in Europe. Concern for children should keep us from doing anything that encourages more instability and abandonment.

This, however, is not a moral message; far from it. It is one of freedom of choice. There is nothing to stop cohabitants marrying, for divorce is easily enough obtained. If they are dissatisfied with their legal lot, why not marry in order to obtain marital rights? And if they are dismissive of marriage as a mere piece of paper, or an unnecessary legal bond, then why are they so keen to turn to the law for compensation when the free union ends? Couples may be trying out their relationship before taking the step of marriage and we should not impose the penalties of a failed marriage on those who were experimenting in order to avoid this outcome. There should be a corner of freedom where couples may escape family law with all its difficulties. Cohabitation is not marriage, now or historically, and people ought to have the freedom to try alternative forms of relationship, not to have one form imposed on them, especially one that treats women as perpetual dependants.

The research shows that cohabiting couples have their own good reasons for not getting married. They have different expectations and intentions and these should be met; indeed, it is time that the expectations of a man entering cohabitation should be recognised to be as deserving of consideration as those of the woman. A unique commitment is made by those who marry and not, as they are well aware, by those who refrain from marrying, and no amount of emphasis on the similarities between spouses and cohabitants can obscure the difference, one of the most fundamental in social existence for centuries, if not millenniums. This is not an argument for the superiority of marriage or even its centrality, but, rather, for the preservation of the freedom to try other forms of relationship, a freedom which at present is being eroded by the increased tendency of the law to impose on the formerly cohabiting couple the status and structure of traditional marriage after they have ended the relationship and therefore at the most inappropriate time.

Legislation in this area is hard because we have no consensus about women in our society. We are inconsistent. On the one hand, we hear that women should expect half of all top jobs and equal salaries; on the other, we hear that a mother's job is to stay at home and that, whether a woman has children or not, living as part of a couple is damaging to her career prospects and that she should be compensated for merely sharing her life for a while with a man. What message would such a bill give to young girls contemplating further education, when it opens the way to huge handouts to women who have been fortunate enough to live with a rich man for a bit while others, equally deserving, will get nothing at the end of a relationship because there are no assets available to be shared?

It would be bad for Bridget Jones; bad for commitment, stability and children; and a breach of the right to private life and the freedom to marry or not. It would create another class of people who just missed out on eligibility because they had not lived together long enough or as a "couple". Some definitions of cohabitation are dependent on probing to test the degree of commitment of the former couple in retrospect.

Research tells us that cohabitants have different perceptions of the union: the man normally does not assume commitment until he has made a clear decision about their future together, whereas the woman will see it in the fact of her moving in with him. Costly litigation, conducted in open court, would rarely be worth it and would open the door to duress at the end of relationships.

What, if anything, should be done to help cohabitants sort out their legal problems? We should recognise their autonomy rather than take it away. Their contracts, if they make them, should be binding; there should be publicity to explain how they may leave their property to each other if that is their wish; that registration of the home in both names will mean an equal split of the equity on separation, and that they could nominate each other as beneficiaries in insurance and pensions. Above all, it should be clear that cohabitation is not a legal status, but a private matter.