Whatever their views about the monarchy, most people will warm to the news of Prince Harry and Meghan Markle’s engagement. Sentimental as it sounds, I was surprised by how much I enjoyed the last royal wedding and how happy I felt for Prince William and Kate Middleton, as she was then. It was one of those rare events when you felt lucky to live in a good country with a bright future. A marriage is, after all, the ultimate statement of confidence in the future — and God knows, we could all do with that right now.

Marriage is not easy and never has been, as Harry will know from his own childhood. Nevertheless, people have always accepted that marital unions and stable families make society healthier, happier and more prosperous. That’s why we celebrate them so publicly, and always have done.

For example, every July at Great Dunmow in Essex, a ‘flitch’ (side) of bacon is awarded to a happy couple who can convince a panel that they have not regretted getting married for ‘a year and a day’. The Dunmow Flitch Trials, which date to the 12th century, represent an early instance of the authorities offering incentives to people to marry and stay together.

Now it’s said that marriage is under threat in British society. It was recently revealed that almost half of children are born to unmarried parents; this figure, however, hides a bit of divergence. For the well-off, marriage rates are high, and have stayed high. It’s for those lower down the income scale that family life is changing.

There was no marriage gap between rich and poor a couple of generations ago, but one has been opening up. The Office for National Statistics divides Britain into seven social classes. According to a study prepared for The Spectator, someone in the top class (i.e., company directors, university lecturers, etc) is 48 per cent more likely to be married than someone in the bottom social class (builders, office cleaners). At the turn of the century, the gap was 22 per cent. To those who think marriage is a quaint irrelevance, such figures don’t matter. But if you think that marriage is the most powerful sponsor of health, wealth and education, then it ought to be alarming. A new inequality is being bred in our society. Why?

Figures for the proportion of children born outside marriage seldom rose above five per cent from the Victorian era right up to the 1960s. Then things started to change. By the time of Prince Charles and Lady Diana’s wedding, in 1981, it was 13 per cent. Since then, it has almost quadrupled. And the decline of marriage has been far more pronounced in working-class areas than in genteel middle England. The Marriage Foundation recently discovered that 87 per cent of mothers from higher income groups are married today, compared with just 24 per cent of those at the other end of the social scale.

Marriage is in very healthy shape for the upper middle class. Indeed, for all their progressive politics, the haute bourgeoisie are highly conservative in their behaviour. Even in the very liberal part of London where I live (82 per cent Remain), few people live what Channel 4 used to call ‘alternative lifestyles’. Sure, most of the mothers go back to work after their children enter full-time education, but then the local schools also depend on volunteer parents, mostly mothers, to be the social glue holding everything together, just as their grannies did. As one of the other local dads said to me, observing the contradiction between how right-on people are in their politics and how traditional in their lives: ‘I like it around here, it’s sort of like the 1950s, isn’t it?’

This is what the sociologist Charles Murray means when he asks that America’s ruling class ‘preach what they practise’; that is, self-control, restraint, monogamy and, if necessary, abstinence. These ideas are unfashionable precisely because the wealthier and better-educated find them easier to live by.

But what explains the social marriage gap? Conservatives tend to blame cultural factors (declining ‘family values’), whereas liberals cite economics. There is truth in both.

Earlier this year, economists at the Massachusetts Institute of Technology found that marriage was a casualty of deindustrialisation. In regions where well paid working-class male jobs had declined, due to technology or globalisation, marriage rates had fallen sharply. In stark economic terms, non-college-educated men struggle to support a family nowadays in much of the West. Indeed, two-thirds of unwed Americans cite finances as a reason for not marrying.

These changing patterns are partly shaped by a welfare state that allows for lower-income women to scrape by with children without the need for a suitable mate, of whom there are now increasingly few available. And scrape by they do. In Britain, 47 per cent of children in lone- parent families live in relative poverty, almost twice the proportion of those whose parents live together. Whether those parents are married or just cohabiting makes a huge difference to life chances, since unmarried couples are six times more likely to break up before their first child’s fifth birthday.

The controversy here is about which way the causal arrow points: are committed and self-controlled people more likely to get married in the first place, or does the act of marriage help keep people together? Is it causation or correlation? The Centre for Social Justice, while admitting it is a chicken and egg question, is confident that ‘even after controlling for socio-economic status and education, research shows cohabiting couples are between 2 and 2.5 times more likely to break up than equivalent married couples’.

For ages, there has been talk about ending the ‘marriage penalty’, whereby the welfare system makes couples poorer together than they are apart. But progress is slow. When Universal Credit was set up by Iain Duncan Smith, the Liberal Democrats were able to say that the single parents who married would be £1,000 worse off.

It’s easy to sneer at the idea of people marrying for money but financial interests have always played a part in people’s decision to marry. Until the industrial revolution, as many as 20 per cent of Western Europeans did not marry at all, largely because of financial inability, rising to a quarter in troubled regions like Ireland.

It may just be that the last century will be remembered as an anomaly, a time when we had a manufacturing-based economy in which working-class men were as likely as their bosses to have families. In Britain, the cost of living, especially housing, puts family formation beyond the reach of many people whose social equivalents a generation ago would have found it manageable. We see, today, something of a return to single living: three times as many millennials are remaining chaste as Generation Xers were at the same age; they are having less sex and fewer relationships, and spending more time on the internet than they do interacting with the opposite sex.

The marriage gap is widening all the time because pregnancy, marriage, and divorce are contagious. If close friends or peers break up, the chances of your marriage ending increase by 75 per cent, according to a 2010 study; people with divorced friends in their social circle are more than twice as likely to get divorced themselves. Likewise, middle-class unmarried men still face social pressure to do the honourable thing and pop the question, not by any overt pressure but by the simple example of their friendship group. For poorer families, that sense of expectation — obligation, even — has diminished, while the wealthier accrue the financial benefits of pooling their resources.

The problems pile up, especially for boys, when they not only lack a father-figure but when everyone else in their social circle does too. Even when middle-class families do break up, the children are more insulated from the blast, more likely to have positive role models to replace a father, and much less likely to be threatened by a violent unrelated male. This makes the game of life, always skewed against poorer children, a complete fix.

How much does the government care? The answer is not very much. About a decade ago, David Cameron said he’d be the most pro-marriage leader the Tories have had in his lifetime, but his enthusiasm cooled quickly. Jeremy Corbyn is unlikely to be talking about family values, which is a shame because a true social justice warrior would be obsessed with this issue. Marriage is becoming a luxury item, a trend that is likely to cause ever-increasing inequality down the generations. Any government that is genuinely concerned about helping those at the bottom should think about what it could do to make marriage for the many, not the few. Maybe free bacon is not such a terrible idea.