BANKS could be flooded with eight million refund claims for unauthorised overdraft charges if they lose the current High Court test case, it was claimed today.

Consumer group Which? said 28% of all current account holders had been hit by the charges since July, 2001, but 63% of these people had not yet submitted a claim to get their money back.

The group claims this means around 8m more people could potentially submit claims for refunds, on top of the 1m claims that have been frozen while the test case goes through.

The research also found that about 42% of people who are waiting for a claim to be resolved are reclaiming sums of £500 or more.

Unauthorised overdraft charges are currently the subject of a test case which was jointly brought by seven banks and a building society and the Office of Fair Trading.

The Supreme Court is due to give its verdict on the case this Wednesday, after the banks appealed against the High Court and Court of Appeal rulings that the charges come under the scope of the Office of Fair Trading.

If the Supreme Court finds against the banks, it will pave the way for a further hearing to decide whether the charges are fair and, if not, what a fair charge would be.

Thousands of consumers had already reclaimed the charges before the test case was launched, with the banks collectively paying out £559m in refunds.

Which? personal finance campaigner Phil Jones said: “If the Supreme Court rules against them, the banks could find themselves staring down the barrel at millions of fresh claims.

“This is in addition to the huge backlog that’s already built up since the waiver was put in place.

“With so much money at stake, the banks may well try to drag the process out even longer, so we’d warn people not to make any plans for their refunded cash just yet.”