Childless and divorced after just three years of marriage, Melissa Miller makes an unlikely standard-bearer for stay-at-home mothers deserted by their husbands. Yet that is what she has become. The law lords’ most important ruling on divorce law for two decades has upheld a £5 million settlement awarded to Mrs Miller by a lower court, not because of her former husband’s adultery, or because she had grown used to a lavish lifestyle as the wife of a fund manager. The ruling, their lordships argued, was intended to enshrine fairness towards spouses of either gender — overwhelmingly still women — who give up work to provide support from home only to see their marriages fall apart.

Mrs Miller’s case is groundbreaking because the law lords decided that the short life of her marriage was irrelevant; the principle of fairness still applied. The case of Julia McFarlane, considered in tandem, is equally significant because it awarded her £250,000 a year from her husband’s future earnings, and not just those of the next five years, as a lower court had ruled.

The McFarlane case offered another important precedent: the conduct of the parties should not be cited as a factor in reaching a settlement, except in exceptional circumstances. In lay language, the days of lawyers rummaging through marital “attics” for evidence of bad behaviour may be numbered. This could bring some consolation to the men whose affairs trigger most divorces, but the broader upshot of yesterday’s judgments is a powerful precedent that will strengthen non-working women in their pursuit of assets from a failed marriage — however brief — for years to come.

Any fresh clarity in a hitherto murky area of law is to be welcomed. Lower courts will appreciate the guidance from above and couples should certainly seek guidance before they commit themselves to marriage. The ruling provides no reason not to marry, but the wealthy, in particular, will need to consider whether a prenuptial agreement is appropriate. This is a somewhat depressing development that would suggest not only that existing divorce law is failing citizens but also that couples are entering marriages that they presume are doomed to fail.

It is also, alas, true that the Miller and McFarlane cases have created as much confusion as they have cleared up. The law lords have justified their generous awards partly as compensation for lost earnings. But they have left unanswered the key questions of when compensation is appropriate and how it should be calculated. Furthermore, they have failed to agree whether business as well as family assets should be counted when dividing up a marital pot.

In these areas, the need for case-by-case flexibility has triumphed over the demands of clarity. Justice, and some well-heeled former spouses, may benefit. Divorce lawyers certainly will. But the middle manager of modest means, abandoned by a spouse who claims and wins a portion of all his (or her) future earnings as compensation for her (or his) hard-to-prove lost opportunities, may rightly feel wronged.

A marriage is a partnership of equals. Should it fail, the parties to the divorce, once it is settled, are likewise equals as citizens, with all the responsibilities that that implies. The law should protect them from greed and vindictiveness. But it should certainly protect the most vulnerable parties in any divorce — the children.