Leading Article: An accountant's guide to sex

Through the thick smoke of moral battle, piercing the mists of social obfuscation comes a new book, with new thoughts for our times. The Rising Price of Love by Dr Patrick Dixon contains the brilliantly simple idea of quantifying the various cash costs, both to the state and to the individual, of the sexual revolution of the mid-20th century.

He reveals for the first time what a huge amount of money we have lavished on permissiveness. For instance, item: Aids care - £710m; item: familial disintegration (alimony, therapy, disturbed children, etc) - £600m. And those are just for starters. Dr Dixon knows that pelvic inflammatory disease, loss of fertility and cervical cancer are all by-products of sex outside marriage, and he costs these too. When added up, the bill for illicit sexual relations comes to a staggering £124bn since permissiveness began (Dr Dixon is prepared to be refreshingly precise about the date) 40 years ago.

It is this same attention to detail in pursuit of high moral standards that has been shown by a Perthshire headmaster, John Robertson, this week. He sensibly introduced a rule whereby pupils of opposite sexes may get no closer than six inches to each other. Best not to inquire too closely about the basis for Mr Robertson's calibrations.

It is greatly to the credit of both doctor and head that they have adopted a hard-headed approach to life, unfashionable since Dickens caricatured it in the person of Thomas Gradgrind in Hard Times. But does Dr Dixon follow through? Why does he leave out a myriad of other costs associated with having (or attempting to have) sex beyond the boundaries of marriage? What about expenditure on cosmetics, clothes, tans and discos, Thai meals and theatre tickets, providing Channel 4, Club 18-30 holidays, amorous phone calls and, of course, the retraining of junior ministers?

The doctor is also timid about policy. Naturally he favours using the tax and benefits system to provide incentives for stable marriage. But why are those of us who are morally correct forced to pay for those who are not? One day the sexually passive and the properly married will arise and riot outside the headquarters of the Family Planning Association, shouting: "Tax breaks for the celibate - no taxation without fornication!"

But the true beauty of the Dixon approach is that it can be applied by both sides of the argument. Balanced against the costs of permissiveness could be those of repressiveness, including, say, the cash consequences of back-street abortions, the care of abused children, the opportunity costs of women forced to stay at home and so on. Once these costs are estimated we could take a rational decision in favour of the least expensive moral climate. How much simpler than agonising over such difficult concepts as empathy, mutual respect, the welfare of children and the long-term good of society. Thank you, Dr Dixon, for cheapening the debate.