More complaints were made about Barclays than any other banking brand by UK customers in the first half of the year, FSA figures show.
The bank received 251,563 complaints, with 53% of closed cases upheld in customers' favour, the BBC reports.
However, Lloyds Banking Group had larger complaints figures when all its brands were added together.
Other brands high on the list included Lloyds TSB (181,907), Santander (168,888) and NatWest (147,109).
Nearly 10,000 complaints were filed every day to financial institutions with the overall number of complaints rising by 3% to 1,852,284 in 2011 H1.
Complaints against firms in the personal investment category, which includes financial advisers, rose to 24,548 in H1 2011 compared to 20,713 in H2 2010 and 20,398 in H1 2010. The mortgage business category also saw a hike in complaints from 22,688 in the second half of 2010 to 29,245 in H1 this year.
Figures were dominated by payment protection insurance (PPI), especially after banks lost their legal challenge on PPI rules in April. However, there was also a rise in complaints in areas including investment bonds where the total reached 12,243 in H1 2011, up from 10,469 during the same period last year.
Income drawdown complaints rose to 1,037 compared to just 708 in H2 2010 whilst complaints in the pure protection category (not including PPI) also rose to 16,428 from 12,465 in H2 2010.
Meanwhile, it has also been announced that Deanna Oppenheimer, who has headed Barclays' UK retail division for the past six years, is stepping down at the end of 2011.
The chairman isn’t answering his email
Reforms not enough
An economic cocktail
To encourage consumers to shop around
Will report to Pat Shea