High housing costs will force an extra 500,000 people to live with their parents into their 30s by 2020, a report has warned.
Research from the Joseph Rowntree Foundation (JRF) published today says the total number of young people still stuck with mum and dad in their 30s will reach 3.7 million.
It says the escalating housing crisis will leave an extra 1.5 million 18- to 30-year-olds will have to accept private renting by 2020.
In just eight years' time the total number of homeowners aged under 30 will have halved, the report found.
Kathleen Kelly, programme manager for place at the JRF, warned of the consequences for those on the lowest incomes.
"Renting is likely to be the only game in town and young people are facing fierce competition to secure a home in what is an already diminished supply of housing," she said.
"With 400,000 vulnerable young people, including families, on the bottom rung of a three-tier private renting system we need to avoid turning a housing crisis into a homelessness disaster."
The JRF predicts that the number of homeless people aged under 25 will rise to 81,000, with further increases expected.
It recommends the provision of more affordable rents and suggests ministers could help by giving tax breaks for landlords who offer longer, more stable private rented tenancies.
The report has been welcomed by MPs on the communities and local government committee, which published its own report on the issue last month.
Chair Clive Betts said his committee had recommended using tax breaks to encourage landlords to invest more readily in building new homes.
Mr Betts said MPs had also questioned the government's affordable rent model, which he said seemed unsustainable beyond 2015 and was already questionable in London.
"We saw untapped potential in the historic grant on housing association balance sheets, and called for clarity on how it could be used to best effect," he said.
"We also urged government to ease centrally imposed constraints upon local authorities, such as on borrowing, to enable them to deliver more homes.
"Taken together these measures, along with others we propose, could boost supply, helping to meet the housing needs of young people in the years ahead."
The JRF report comes amid a row over housing between Labour and the government, after shadow housing minister Jack Dromey accused housing minister Grant Shapps of misleading use of statistics.
Mr Shapps, Mr Dromey said, "hailed yesterday's shocking official statistics showing affordable house building collapsing 68% over the past year as progress".
He added: "And he believes basic protections for private sector tenants are nothing but 'red-tape'.
"On housing the Tory-led government is not just out of touch but utterly incompetent."