About 31% of people said the rate of interest they paid on credit card debt had gone up in the past 12 months, according to moneysupermarket.com.

A number of major players, including MBNA, Capital One and Barclaycard, have all raised their rates for at least some of their customers during the past year, with MBNA now charging a small number of people as much as 34.95% on an annual percentage rate basis.

Financial information group Moneyfacts.co.uk said since April it had seen a marked increase in the number of lenders increasing their charges.

It said 19 credit cards had increased the interest they charged people on purchases since April, while 14 had increased the rate charged for cash advances and eight had bumped up cash withdrawal fees.

Most increases in purchase rates have been around 1% or 2%, with some as high as 3%.

A further five providers have increased balance transfer fees, three have raised their foreign usage charges, one has increased its account fee and two have reduced the minimum monthly repayments they require, meaning consumers could end up paying more interest on their debt over the long-term.

The increases come at one of the busiest periods for credit card usage as people head off on holiday.

Credit card companies are currently facing higher lending costs as a result of the credit crunch.

At the same time, the Office of Fair Trading has capped the fees they can charge for late payments at £12, while sales of lucrative payment protection insurance are thought to have been hit by the recent spate of negative publicity surrounding the product.

Michelle Slade, analyst at Moneyfacts.co.uk, said: "Credit card companies usually tend to shy away from increasing the purchase rate as this is the headline rate all consumers will look at.

"Many card companies have preferred instead to increase the rates and charges that many consumers may take little notice of when selecting a card."

lOpinium Research questioned 2,018 people.