A generation ago more than a vestige of disapproval still lingered in the phrase “living in sin”, and unmarried couples were at odds with accepted social convention. Today there are at least two million cohabiting couples, and the term “partner” has become a normal official description of either of two people, regardless of gender or marital status, who live together. But though social mores have changed, the law has not kept pace. And whereas divorce law entails a panoply of arrangements to protect children, recompense those who sacrificed careers and determine alimony, when cohabiting couples split up there are few enforceable rights for either party.

Pressure to change the law has been growing, especially since the passage of the Civil Partnerships Act which offers legal rights to homosexual couples. This measure rightly acknowledged that gay couples were entitled to underpin their relationship with the same rights of inheritance, tax benefits and next-of-kin recognition as married couples. When the law was passed, however, such rights were denied to cohabiting heterosexuals on the grounds that they could, at any time, get married. That answer may have been logical, but it failed to still a sense of unfairness. Many couples think that the term “common law spouse” gives them rights. It does not.

The Government is therefore now proposing to look again at the implications of cohabitation, and especially at legal protection for those who suffer financially – almost always women – when the relationship ends. Next month it is to publish proposals to allow unmarried men or women to make claims against partners for loss of earnings, to win a division of property, regular maintenance payments or a share of their partner’s pension when they separate.

At the heart of all these plans must be the arrangements for children. It is here that all financial arrangements, visiting rights and maintenance payments matter. What children need is stability, and the commitment of marriage is preferable to ad hoc arrangements, some of which may indeed be enduring and provide a loving environment but which do not necessarily have the starting point of long-term commitment. A partner who misses out on a financial payday is far less a victim than a child raised in an unstable environment. Too often divorce today is about property, lifestyle and spending money. Recent huge settlements have focused on the trivial and the dishonourable – who gets what, how lavish was the lifestyle, how greedy are the claimants. Such cases overlook the real damage of divorce: the hurt of the children, their loss of opportunity and the breakdown in parental relationships.

Proposals to give legal rights to childless cohabiting couples should not become a route to riches for the unscrupulous. Little detail is yet given on how long a woman has to live with a man before he or she can claim maintenance. It would be outrageous if, say, a year were enough to trigger a vast pay-out by the wealthier partner. The young and foolish should not be penalised for mistakes.

If sensibly applied, however, the new law may strengthen, not weaken, marriage. Those hoping to shirk responsibility by not formalising a relationship will find themselves just as liable when that relationship ends. So why not marry? What the new law should do is to make them think harder about marriage before having children. More importantly, it should protect those children who are born to the unmarried. They are always the victims of separation.