Barclays received the most complaints among Britain's banks in the first half of this year, though complaints overall in the sector fell 5%, the country's financial watchdog said today.
The most complained about product was payment protection insurance - insurance on loans.
UK banks have already set aside about £20 billion to pay compensation for mis-selling the product.
There were 278,426 complaints about Barclays, down 10% on the first half of 2013, while Bank of Scotland received the second-highest number of complaints, up 46% to 265,640 over the same period.
"It's important that firms now get on top of the issues that are driving complaints," said Christopher Woolard, director of policy at the Financial Conduct Authority.
"Although it's encouraging to see the total number of complaints fall, there is clearly further work to be done toe nsure that consumer interests come first," he added.