Credit cards have been a growing source of vexation
More than half of those who complained to the Financial Ombudsman Service (FOS) in the last financial year won some compensation.
The FOS annual report said there was a 14% increase in the number of disputes it decided, at a record of 114,000.
Of these, 57% went in favour of the complainant, a far higher proportion than in the past.
The topics producing more complaints were credit cards, payment protection insurance, loans and consumer credit.
Sir Christopher Kelly, chairman of the Ombudsman service, said the recession was producing many more disputes.
"For us, it has involved dealing with a significant increase in the number of complaints arising from the impact of the worsening financial climate," he said.
"As businesses tighten their belts - and the credit crunch leads to increased financial difficulty for many consumers - we are gearing up to deal with further volatility in complaint volumes," he added.
The financial ombudsman exists to sort out disputes between financial services firms and their customers if a complaint to the firm cannot resolve the issue first.
The report highlights the increased number of complaints about credit cards - nearly 19,000.
The 32% rise was partly because of default charges applied where someone had to pay extra for missing a repayment date or spending over their limit.
But the rise in card complaints was also driven by more borrowers being aggrieved that their card company had suddenly increased their interest rate, in some cases by as much as 10 percentage points.
"As part of our investigation into these complaints, we issued questionnaires to the credit-card companies involved, to obtain information about - among other things - the actual assessments of risk that had been carried out in relation to these customers, and how the new rates had been calculated," the Ombudsman reported.
"Almost all the credit-card companies subsequently chose to settle the complaints that had been brought against them, rather than have our investigation continue," it reported.
The consumers organisation Which? said it was shameful that some firms were rejecting claims that were later upheld.
"This could be just the tip of the iceberg as many people give up at the first hurdle rather than going to the Ombudsman," said Doug Taylor of Which?
"Companies have a duty to treat their customers fairly and this means giving all complaints due consideration and, if appropriate, accepting them."
Overall, there was a particularly high success rate for people who complained to the Ombudsman about either their credit card issuer or about payment protection insurance.
More to come
The Ombudsman's annual report shows that the overall number of new complaints which arrived during the year rose 4% to a new record of 127,471.
NEW COMPLAINTS MADE IN
2008-09 TO FINANCIAL OMBUDSMAN
Credit cards - 18,590, up 32%
Current accounts - 13,682, down 65%
Mortgage endowments - 5,798, down 58%
PPI - 31,066, up 191%
The six biggest financial services groups, the Ombudsman said, generated half of all the disputes his organisation received.
The 2008-09 year saw an 11% rise in new complaints about mortgages, particularly about the handling of arrears.
Disputes about mortgage endowment policies continued to fall and were down by more than half on the year before.
Complaints about current accounts dropped by two-thirds because of the continuing High Court test case on overdraft fees and the freeze on new claims.
However, complaints about payment protection insurance nearly tripled, to just over 31,000.
Nearly all the PPI cases resolved in the past year - 89% - were found in favour of the customer.
The future sale of the policies will now be severely restricted, following recent decisions by the Financial Services Authority and the Competition Commission.
But the Ombudsman's report commented that "there is still a widespread problem involving businesses rejecting complaints that they know, or should know, we will uphold".
"This only adds to the inconvenience suffered by consumers," it added.
Last month the Ombudsman, Walter Merricks, complained that some firms were cynically trying to stop dissatisfied customers taking their complaints further by being deliberately unhelpful.