Credit card debt is rising as consumers stick to minimum repayment levels, latest research has claimed.

A study by the University of Warwick found that people are reducing the amount they repay each month because of minimum repayment sums on credit card bills.

It warned that this trend could double the amount of interest consumers pay during the lifetime of their debt.

The research focuses on 'anchoring', a psychological phenomenon under which arbitrary and irrelevant numbers bias people's judgements.

It said this affects the way people repay their credit card bills, reducing repayments each month for the third of cardholders who pay back neither the full amount nor just the minimum.

Psychology researcher Dr Neil Stewart said: "These results should be of real concern to credit card companies.

"Virtually all credit card statements include minimum payments. But this consumer safeguard has an unexpected negative consequence: minimum payments distort the behaviour of many customers in a way that increases interest charges and increases the duration of their debt."

The study of 248 real credit card bills revealed that 58% of people repaid their balance in full, suggesting they were unaffected by the minimum repayment figure. But 7% paid only the minimum, while 36% made a partial payment above the minimum but below the full balance.

A close correlation between the amount repaid and the minimum repayment level was found to be prevalent in the third group.

The research was supported by an experiment in which 413 volunteers were given mock credit card bills for £435.76, but only half had a suggested minimum repayment. People were asked to say how much they would repay based on their current financial situation.

The experiment found that the minimum repayment level had no impact on people who decided to clear their bill in full.

But where a suggested minimum repayment was given the amount paid by those not clearing the debt sunk to an average of just £99, compared with those whose bill did not contain a minimum repayment figure, who repaid an average of £175.

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