Payment protection insurance (PPI) complaints are on course to more than double the record number already predicted for this year, the ombudsman service has said.
The Financial Ombudsman Service (FOS) has already received nearly 100,000 PPI complaints in the first six months of this financial year and warned that consumers would only face longer waits for justice if banks failed to clear up complaints quickly and fairly.
The flood of complaints to the ombudsman has also shown a dramatic increase, with 66,882 new complaints made about PPI between July and September, more than double the 32,445 complaints received in the first quarter of this year.
A spokesman for the FOS said that with 1,500 new complaints a day and well over 3,000 new telephone inquiries a day as well, it looked "likely" that the ombudsman would see more than double the 165,000 cases that it had originally anticipated.
The service said it had built enough flexibility in its budget to sort out far more cases than the original estimate, but even so, this left the watchdog tackling much higher complaint volumes.
Around £10 billion has been set aside by the banks to cover claims being made by people who were sold insurance they did not want or need, but some consumer groups have raised concerns that even this could not be enough to cover the scale of the problem.
PPI policies were meant to help people pay back their loans after a loss of income, but a widespread mis-selling scandal emerged, with some people finding they had taken out the insurance without realising it or felt under pressure to do so.
Consumer group Which? has been leading the "Big Change" campaign to alter banks' culture.
Which? chief executive Peter Vicary-Smith said: "The banks must set aside more money for PPI claims and make it easier for customers to get back what they are rightly owed, without any hassle.
"Consumers are continually being short-changed by the banks. We're campaigning for Big Change in the culture of banking to put customers first, not bankers and protect the public suffering from further mis-selling and scandals."