The report went on to criticise credit card companies for making it hard for customers to compare different rates and find the best deal. The Office of Fair Trading wants companies to provide easy-to-understand summaries of their offers and not confuse customers with terminology.

John Fingleton, Office of Fair Trading chief executive, said: "No one wants to throw money away, but consumers who don't shop around for credit cards are doing just that. It is essential that consumers are given the right tools to make comparisons between credit cards more easily."

This follows an estimate by Moneyextra that 5.9 million cardholders have changed their credit card in the last six months and could have benefited from 0% interest still available on some deals.