A regulator has warned home owners on interest-only mortgages that they are facing a "wake-up call" because up to half of these borrowers will not have enough money to pay their loans back.
The Financial Conduct Authority (FCA) fears that consumers are under-estimating the scale of the problem.
Around 260,000 people are thought to have no strategy in place for repaying their loan.
Consumer campaigners also raised concerns that a "significant" number of people claimed to be unaware how their loan was meant to be paid back when they took the product out.
Mortgage lenders have agreed to alert at-risk customers to help them avoid "payment shocks".
Some people may have to sell their home to pay the loan back unless they control their repayment planning.
With around 2.6 million interest-only mortgages, some 10% of people have no plan for repayment.