The Klarna site lists retailers such as Asos and H&M which let buyers pay later for their goods.

As part of Klarna’s instalments scheme, shoppers can spread the cost of a purchase in three equal payments over 60 days.

There are no charges, fees or additional repayments to delay settling the balance at a later date.

However, shoppers have reported seeing charges on their credit card statements relating to purchases made under the instalment scheme.

Swedish firm Klarna (which translates to ‘clear’), said it is aware of the problem, having seen this charge applied by Tesco Bank, as well as Halifax and Bank of Scotland. It added that it is not specific to certain retailers, but is based upon the customer’s bank.

Its T&Cs also state that some card issuers may levy a fee, typically a cash advance fee, similarly applied when a credit card is used for gambling.

Luke Griffiths, general manager at Klarna UK, said: “We would like to make it clear that Klarna is not charging this fee – it is the banks themselves. The root cause of the issue is thought to be that the card issuers are classifying Klarna’s Instalments product in a way that allows them to levy a cash advance fee according to their own terms and conditions. Klarna is working with providers to try and resolve this issue as soon as possible, but it will need to be a combined effort, as we are unable to solve it alone.”

Griffiths advises that if customers have been charged a fee, they should contact their bank and raise a dispute.

“We also advise that they should change the card associated with their Instalments account. By changing the card to an alternative provider, this will stop the issue,” he added.

A Lloyds Banking Group spokesperson, said: “We do not charge fees for transactions paid to Klarna and we haven’t received any customer enquiries or complaints on this topic; we encourage customers to get in touch with us directly if they would like to discuss any fees on their statement in more detail.”

A Tesco Bank spokesperson, said: “We’re always sorry to hear about customers who have been charged unexpectedly. We charge a fee when customers use their credit card to repay borrowing. This means using our credit card to make payments to buy now pay later schemes will be subject to a fee.

“Our customers are not charged this fee when these payments are made with their debit card. A full list of payments that are classified as cash transactions can be found in the terms and conditions of the credit card and on our online Your Community forum.”