Payment Protection Insurance (PPI) has topped the list of complaints to the financial ombudsman service, with 30% of new cases during 2009-10 relating to it.
In total, the ombudsman resolved 46% more finance cases than a year before.
The service handled 925,095 enquiries from consumers in the last financial year, resolving a record 166,321 disputes.
In half of the cases, consumers were given compensation.
In all, 49,196 new complaints were about PPI.
The Competition Commission confirmed its intention to ban PPI being sold at the time loans are granted, despite complaints from leading lenders.
James Daley, of Which? Money, commented: "Many people give up at the first hurdle rather than going to the ombudsman.
"It also reinforces the need for the Financial Services Authority to push ahead with plans to force firms to review rejected PPI complaints."