Legislation limiting the amount of interest that can be charged on credit card debts is being promised by the Labour Party.
Under the changes, nobody would pay more in interest than they had originally borrowed.
Shadow chancellor John McDonnell says more than three million people are “trapped” by credit card debt.
He will unveil the planned change in the law in a speech at Labour’s conference in Brighton.
Labour said the changes would work in a similar way to measures on payday loans, which came into force in 2015.
The Financial Conduct Authority has called for new measures to help people in “persistent debt” as a result of credit cards.
The regulator says over three million people are in persistent debt, which it defines as having paid more in interest and charges than they have repaid of their borrowing over an 18-month period.
Labour said its “total cost cap” would help “tackle the persistent debt spiral”, claiming growing consumer debt was becoming a “threat to our economy”.