A lack of affordable homes is forcing young Britons to live with their parents

Choosing when to leave home isn’t easy. Independence has to be balanced against security. The freedom of a space of your own weighed against the responsibility of doing your own laundry.

But in the United Kingdom that decision is now being made later and later, and many young people are finding the cost of leaving home is taking away their choice altogether.

Nearly a million more young adults aged 20-34 are living with their parents compared to 20 years ago, according to analysis by the think tank Civitas. In 1997, just one in five of that age group were still living at home. By 2017, it was one in four.

The knock-on effects are dramatic. For many decades, household size in the UK was falling, and the number of households per capita was rising. But since the turn of the century, those trends have reversed. Such a major shift begs the question - are children just choosing to live at home longer for lifestyle and cultural reasons? Or are financial pressures forcing people to stay with their parents for longer than they would like?

The cost of housing has risen dramatically across the UK as a whole, while earnings have stagnated since the global financial crisis of 2007/8. The average home now costs nearly eight times average annual earnings, compared to less than four times 20 years ago. Private rents are now deemed unaffordable for average working families across half of England.

But it is the regional variations that give the best clue. Simply put, more young adults are living with their parents in areas where housing costs have gone up most - particularly in London. But in regions with much lower growth in housing costs, like north-east England, the rate has changed relatively little in 20 years.

Even when young adults are waving farewell to their parents, increasingly they are moving in with friends or partners. The proportion of single person households has fallen to just 30%, compared to 35% in France and the Netherlands, and 40% in Germany and Denmark.

All this points to a shortage of housing. Successive governments have been blamed for failing to ensure housing supply has kept up with demand. The current government is promising 300,000 new homes a year by the mid 2020s, but there is a long way to go. By some counts, as many as 4 million more homes are needed in England alone. And the authors of the Civitas report argue that the number of young adults living with parents has actually hidden the true scale of the shortfall.

Young Britons are not alone in feeling shut out of the housing market. In the United States the so-called boomerang generation has grown since the global financial crisis: nearly one in five men between 25 and 34 are back living with their parents (although only one in eight women).

There is a huge variation in the average age that young adults leave home that cannot be explained solely by financial factors. Within Europe, Scandinavians tend to fly the nest earliest, with young Swedes moving out at an average age of 21. Italian, Greek and Spanish parents host their offspring for much longer, but it is the countries of the former Yugoslavia that hold on the longest - the average Montenegrin is past their 32nd birthday before they make a move.

Different cultural factors are at play across the rest of the world. In India, where it is common for young men to stay in the family home until, and even beyond, marriage, more than 80% of urban 20-somethings still live with their parents.

In China the cultural expectation that people will look after their parents and grandparents as they get older also encourages multi-generational households. But, in what can be interpreted as a sign of the status accorded to owning property, Chinese millennials have among the highest rates of home ownership in the world.

Many cultures celebrate different generations living together, and when it is a free choice, then it can also make financial sense. But if the living arrangements are forced by a lack of affordable housing, the consequences can be far reaching: even affecting the mental health of frustrated young adults, the financial security of their parents, and the harmony of the family as a whole. Particularly if mom is still expected to do all the laundry.