A generation of "forgotten families" risks being priced out of the housing market in England without a dramatic expansion of shared home ownership, a charity has warned.
Up to 1.8 million middle-income families earning between £20,000 and £40,000 could find themselves stuck on the first rung of the property ladder or facing the prospect of years of private renting, Shelter said.
Almost three-quarters of them will be unable to buy a family-sized home because of the rise in property prices, a report by the charity concluded.
Its data suggested the Government's Help to Buy scheme - which offers loans so people can purchase new-build homes with a deposit of 5% - will still leave a large number (78%) "priced out".
More than three in four families on low or average incomes will not be able to cover the monthly mortgage repayments on a family-sized home, even if they have the funds for a deposit, Shelter found.
"This means that the only option for many will be years spent bringing up children in private lets, paying out dead money in rent and facing the insecurity of short-term tenancy contracts of just six or twelve months," the charity said.
According to Shelter's analysis, one in four families on low or middle incomes would be privately renting by 2020, with many more likely to be trapped on the first rung of the ladder in homes that are too small for them. But it found 95% of families on low or middle incomes could afford mortgage repayments for a home where ownership was shared.
It is now calling for a major new house building programme. An investment of £12 billion could build 600,000 new shared ownership homes, the charity said.
"So far, years of piecemeal policies and an alphabet soup of confusing schemes have meant that shared ownership has failed to reach its potential, leaving it nowhere close to meeting the needs of England's forgotten families," Kay Boycott, director of campaigns and policy at Shelter, said.
"But for the many young people desperate to do what generations have before them and find a stable home of their own, a national shared ownership programme is the bold and radical solution we need."