Love and marriage, go together like a carriage and horse. Is that quite right? Does marriage plus a £20-a-week tax break equal love? Because if you could buy the quality that makes stable families, you would certainly buy love, not marriage. Where love and support are abundant, a family will flourish. Where they are absent, it will not.

This week, in a report called Every Family Matters, Iain Duncan Smith’s Centre for Social Justice (CJS) repeated its demand, which is now Conservative party policy, that marriage be recognised in the tax system. It is strange to see Conservatives, who usually disparage the capacity of government to make the world a better place, turn into Ed Balls when it comes to marriage.

Most of the report is unobjectionable. We’re all in favour of “saving saveable marriages”. Add this to eating edible apple pie and weathering a sunny day. A three- month “cooling-off period” for couples on the brink of divorce is reasonable enough, although the counselling will come too late for most and the suggestion that warring couples be taught the implications of their decision is fabulously patronising.

But there are two serious problems with the idea of promoting marriage: it doesn’t work in practice and, worse, it doesn’t work in theory either.

The expressed point of the policy is to make more people get married and stay married. The argument goes like this: the divorce rate since the 1970s has been calamitous. Cohabitation, an inferior and more volatile state than marriage, has risen 65 per cent in a decade. Married people are more likely to do good things and less likely to do bad things. They are more likely to be wealthy, in good jobs, keep their children out of prison and so on.

In fact, as a Cabinet Office report from December of last year showed, it is all but impossible to establish a causal link. Once you control the data for income, wealth and education, the marriage effect is very small. The children of the poorest 20 per cent of married couples, for example, do much worse than the children of the richest 20 per cent of single parents. We know that happy and committed cohabiting parents have — surprise, surprise — happy and well-adjusted children.

We know, in any case, that people with more money, higher education and better mental wellbeing are more likely to get married. The CJS report says blithely that “those who are married are statistically more likely to be law-abiding”. How about “those who are law-abiding are statistically more likely to be married”? Is that any less true? Maybe someone in Mr Duncan Smith’s office pressed a button and deleted the word “happily” throughout. Of course people who are happily married tend to have better lives than people who are not. So do people who are happily unmarried.

The CSJ also says that “the decline in marriage since the 1960s has been accompanied by a rise in a number of serious social problems”. Yet throughout the period in which the divorce rate took off there were incentives in the tax system for people to be married. Didn’t exactly work, did they? And since the incentives were abolished, the divorce rate has fallen. In 2007 in England and Wales it was the lowest since 1981. Nine European nations have higher divorce rates than the UK. After an exhaustive review of international data, a Department for Work and Pensions report concluded recently that “on balance ... there is no consistent and robust evidence to support claims that the welfare system has a significant impact upon family structure”.

For the CSJ, the conclusion is leading the data, not the other way round. But even if you don’t mind your social science shoddy, the policy will never work. For a start, only 25 per cent of families with children are headed by married couples with one person working and one not — the only families that would benefit from the Tory plan. Unemployed married couples don’t get it. Nor do married couples who both work. Get back in the kitchen, one of you.

And given the supposed size of the problem, the scale of the tax break is derisory. I don’t mind being bribed but I do mind being considered such a cheap date. The biggest source of marital breakdown in this country is money. The marriage service asks people to commit “for richer, for poorer”. They should specify “for richer”. Poor people are much more likely to get divorced than rich. If you want more people to be married, you would be better off ensuring that there were fewer poor people around than you would “recognising” marriage in the tax system.

It looks as if the Tories wouldn’t “recognise” a bad policy when it’s giving £3.2 billion of our money away. This policy would reward a man who leaves his wife and remarries. The widow is greeted by the State for the loss of her husband with the loss of her tax break. Three children growing up in greater need to loving cohabitees get nothing while the Duke and Duchess of El Dorado pop down the post office to pick up their £20.

And imagine that your objective was to increase the divorce rate. I can think of no more forensic policy than to take the set of current cohabitees and make them get married. This bunch of flaky no-hopers all of a sudden commits for life because of the power of the vows and the promise of a few quid? Oh, come on.

And what about those people for whom divorce is a good idea? Before we make a fetish out of family life, a word needs to be said for all those women and children who grow up in appalling families in which the departure of an abusive husband and father comes as a blessed relief. The big problem with Every Family Matters is that it’s not true.

This is the philosophical objection to a marriage policy. We ought never to look after the health of the flock by neglecting the sheep. Children matter more than families. So do wives and so do husbands. That does not mean we have no responsibilities, of course we do. But it does mean that politicans ought to be careful before they enter our lives with a fistful of dubious causes and start supplying us with a half-baked idea of the good life while all the while professing it to be universal and natural. It’s love that counts, not marriage. Horse first, then carriage.

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