According to figures released by the Financial Ombudsman Service (FOS) - which typically deals with 150,000 disputes a year - around 900 disgruntled customers are voicing their frustration on a daily basis.
Indeed, between April and June, 81,000 individuals contacted the industry referee - a total more than double that recorded across the same period one year earlier.
In more than half of the cases, the watchdog took the side of the customer, while almost seven out of ten instances centred upon payment protection insurance (PPI).
Such complaints were sparked when people who opted for PPI discovered they were unable to claim following time away from work due to sickness and unemployment.
An FOS spokesman commented: "More and more are aware of the ombudsman but many complaints should have been dealt with by the bank or insurance company."
By Asim Shah