2.6 million interest-only mortgages are due to be repaid over the next 30 years, but over a third of borrowers surveyed say they might not have enough cash to do so.
The Financial Conduct Authority thinks that figure is under-estimating the problem.
It claims more than a quarter of a million people are thought to have no strategy in place for repaying their loan.
Brian Harris is Director of Mortgages for Christians.
He told Premier's News Hour more about the situation.