A judge yesterday ordered two high steet banks to disclose how much it costs them to deal with customers who exceed their overdrafts. Consumer groups say this could lead to banks revealing the ‘true’ cost of overdraft charges for the first time.

Judge Ian Beresford said that Yorkshire Bank and Alliance & Leciester should make full disclosure about their charges by September 28 as he presided over direction hearings for seven bank customers seeking to reclaim their overdraft charges. Banks and building societies charge up to £39 for customers who go overdrawn without permission or bounce payments.

Judges hearing similar cases have asked for such disclosures before, but the banks have always settled with their customers out of court before the deadline for making the disclosure passed.

But consumer groups say the seven cases were unusual as Yorkshire Bank sent lawyers to represent it at the directions hearing and the seven claimants were represented by a specialist QC, funded by moneysavingexpert, a consumer website and the Consumer Action Group.

Martin Lewis, from moneysavingexpert.com said: “If I were in the position of the Yorkshire bank I would feel that I had a diificult choice. Either a massive climbdown to settle out of court, or breaking ranks with other banks to reveal their internal costs structures.”

Judge Beresford said he felt as if he was the first judge to see "more of the picture". "There is a number of issues coming through nationwide. What we want to try and do is narrow the issues down so that if necessary the matter can go to trial," he said.

Hundreds of thousands of banks customers have already reclaimed six years’ worth of bank charges from their banks, and millions more have downloaded template letters to help them to reclaim bank charges. But they are not always receiving the refunds they claim. Lloyds TSB became the first bank to successfully defend a customer's claim in court in May, and other banks have done the same since then.

Mr Lewis said: “Consumers need to remember that 80 to 90 per cent customers are receiving refunds for overdraft charges just by writing a letter. There is a chink in our 100 per cent success rate, and we are trying to stop it.”

Yorkshire Bank refused to comment on whether it would disclose overdraft costs. A spokesman said: "We believe our charges are fair and legal. Customers agreed to them when opening their accounts."

A spokeswoman from Alliance & Leicester said: “ We say our charges are fair and legal. We will need to study papers from the judge before we decide how to proceed.”