The eight major providers have all been found guilty of this practice by the comparison site, which singles out Nationwide as one of the few exceptions. And this apparent foul play means that many credit card customers are unaware how much credit is really costing them.

Head of credit cards, Steve Willey, explains. “Take the case of someone who did a £2,000 balance transfer at 0 per cent and then spent another £1,000 on the card,” he says, “If they then paid off £2,500, the remaining £500 balance would accrue interest at the typical APR (usually around 15.9 per cent) rather than continue to enjoy a 0 per cent rate.”

Mr Willey explains the importance of understanding the terms and conditions of each credit card. “Credit card providers are quick off the mark to attract customers with 0 per cent deals. However, they are much slower when it comes to educating people on what that 0 per cent actually means.”

However, he points out that Nationwide treats customers in a more transparent way. “It is yet to make an impact in the credit card arena – where it only has two per cent of the cards in issue – so simple actions like this should help it grow market share,” he comments.

“Consumers really need to stay one step ahead of the game if they want to avoid lining the pockets of the banks,” warns Mr Willey, highlighting the importance of comparing deals and finding out which cards are best for making purchases and which offer the best balance transfer deals.

© Fair Investment Company Ltd