THEY say that marriage is for life - but children should definitely move on. So how easy is it when the children are at home, but no longer children?

They are called the "boomerang generation" - those who have left home, but now find themselves back there. Figures from the Office for National Statistics reveal that more than a quarter of those between the ages of 20 and 34 - that is 3.35 million souls - lived in the parental home last year.

The reasons are not hard to discern: they include unemployment, rising house prices, and the rising cost of living. The statistics are bleak, and so sometimes is the social life. Mandy, aged 25, has been forced to move back to her parents' house after four years away, and tells me that it has been difficult.

"The trouble is", she says, "I see less of my friends now. They don't live near, and I can't go out like I used to. . . I feel like I have to be around for supper. My mum and dad don't say that, but it's how I feel. It's at 7 p.m., and I shouldn't be late. I'm getting a bit tetchy with them, I know that."

In Continental Europe, this is the cultural norm. In Spain, 55 per cent of 29-year-olds live with their parents; in Italy, it is 60 per cent. So it is not a news story there, but it is one here; because, for the UK, it is a new, unwelcome reality.

Behind these statistics are often dark feelings. As the psychologist Dr Lynne Jordan writes: "If the reason for moving back home is something that is potentially embarrassing, such as the loss of a home, job, or relationship, the humiliation a person feels is likely to be worse."

The return to a childhood bedroom is not experienced as a happy homecoming; he or she is there because, in their eyes, they have failed, and these four walls are a daily assault on their self-image.

There can be positive aspects. Some celebrate the money that they are saving, and make plans: perhaps, in a couple of years, the Help to Buy scheme can come to their aid, if they can put some money away. And some parents may also be happy. If they have found it a bit lonely since their offspring fled the nest, there can be delight in their return, and a new way of knowing their children.

But the relationships may also be tricky: people tend to regress on returning home, and old patterns re-establish themselves. "It depends on how well the various developmental stages were successfully negotiated in the growing-up years," Dr Jordan says. "If someone has a strong sense of self as an adult, and had a good relationship with their parents . . . they may be fine."

The poet Robert Frost said: "Home is the place where, when you have to go there, they have to take you in." True. But that does not mean that the homecoming is a happy one.