More than 260,000 people were at least three months behind with their mortgage payments in May, according to the Council of Mortgage Lenders.
It has warned that the total number behind with payments could rise to more than 400,000 by the end of the year.
There is concern that some lenders might see such people as a useful source of profit, charging them while they struggle with their debt.
Consumer organisation Which? wants the regulator to make public the names of the worst offenders.
We discuss the issues with Dominic Lindley of Which? and Sue Anderson of the Council of Mortgage Lenders.