Leaving the parental home has increasingly become a "rite of passage" in the past two decades, replacing marriage as the defining event of independent adulthood, according to research from the University of Edinburgh's Centre for Educational Sociology.

Leaving Home, a book by Gill Jones, deputy director at the centre, argues that young people are leaving home in their late teens in ever greater numbers, either because of family conflict, or to study or take up employment. In Britain, more than half of young people have left home by the age of 21, often not by choice.

The book draws on British and international studies, as well as new evidence from recent large-scale national surveys and in-depth interviews.

After leaving home, young people rarely set up new households, but live in a variety of "intermediate households", such as hostels or nurses' homes, or staying with relatives or friends. Leaving home is an expensive step, and so under-18s are at particular risk from homelessness, as they frequently lack the incomes to set up home. The risk of homelessness is increased when leaving home is not a matter of choice.

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Housing demand has become greater and more varied, but the market has become more polarised. Housing is available to those wealthy enough to buy property or those poor enough to qualify for social housing, but little is available to those in between, a shortage which impacts on ÖйúAƬ. "Students are more and more competing with other young people for the limited housing available," said Dr Jones.

However, benefits, grants, and other support systems have not kept pace with this social transition. Coupled with the higher proportion of young people leaving home early in order to study, more young people are forced into financial dependence on their parents.

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Young people do not have a legal right to live in their parents' home after the age of 16 in Scotland and 18 in England and Wales. Some parents either may not be able to or may not want to help their offspring set up home.

Dr Jones is alarmed at the implications for students and other young people of competing for a small range of housing. "I don't think we can afford to create a generation of people who have a double disadvantage," she said.