The Financial Ombudsman Service (FOS) was inundated with a record number of complaints last year.
The ombudsman received 206,000 formal complaints in the 2010-11 financial year, a rise of more than a quarter (26%) on the previous year.
FOS steps in to settle disputes that can not be resolved between financial businesses and consumers.
More than half (51%) of new complaints were about the sale of payment protection insurance (PPI), with the 104,597 cases making it the highest number ever received in a year for a single financial product.
Following the collapse of the bank's challenge against PPI payouts, it is expected that billions will be paid out to consumers that took the insurance cover.
Natalie Ceeney, the chief executive and chief ombudsman, said the last financial year was the busiest in its decade-long history as it received more than a million consumer enquiries, one in five of which turned into a formal dispute.
"This reflects the increased confidence of an ever more diverse range of consumers getting in touch about a wider range of problems and issues," she added.
"Aside from PPI cases, over the year we've seen encouraging signs of improvements in the way that some businesses are handling complaints.
"And it's good to see that the number of disputes about some other financial products has started to fall."
More than half (51%) of the cases that the ombudsman got involved with resulted in compensation being paid to consumers, with half of all disputes being settled within three months.
Complaints about investments fell by 30%, while general banking complaints fell by a tenth.
There was also a drop in complaints about health insurance, current accounts and home contents insurance.
By contrast, complaints about consumer credit, travel insurance and motor cover increased.
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