A study carried out by Warwick University found that the presence of minimum repayment sums on credit card bills caused many people to reduce the amount they chose to repay each month.

It warned that the impact of minimum repayment figures could double the amount of interest consumers paid during the lifetime of their debt.

The research centres on the psychological phenomenon of "anchoring", under which arbitrary and irrelevant numbers bias people's judgments.

It found that "anchoring" effects the way that 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."

A study of 248 real credit card bills which were looked at as part of the research showed that 58 per cent of people repaid their balance in full, suggesting they were unaffected by the minimum repayment figure.

But seven per cent paid only the minimum, while 36 per cent made a partial payment above the minimum but below the full balance.

The third group was found to be highly influenced by the level of minimum repayments, with the amount they repaid closely correlated to the minimum repayment level.

The research was backed up by an experiment in which 413 volunteers were given mock credit card bills for £435.76, half of which had a suggested minimum repayment and half did not. People were asked to say how much they would repay based on their current financial situation.

The experiment found 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 plummeted to an average of just £99, compared with those whose bill did not contain a minimum repayment figure, who repaid an average of £175.

Dr Stewart calculated that based on the experiment, the inclusion of a minimum repayment figure on a credit card bill could double the amount of interest paid over the lifetime of the debt.

He said: "Although minimum payments are a good idea in principle because they protect the small number of people who would otherwise make no repayment at all minimum payments do seem to have an adverse effect on those who repay only part of the bill, even those repaying a large fraction of the bill.

"From the psychology of anchoring, we know that people are less susceptible to its effects when they have greater knowledge.

"So helping people understand how much different possible repayments will cost them in the long term should help protect them from anchoring on minimum payments."