Barclays was the most complained about bank between July and December 2013, according to the latest data from the Financial Conduct Authority (FCA).
During the six-month period Barclays received 309,494 complaints from customers, although this was a decrease of 17% compared to the first half of 2013.
Most of the complaints made this time related to PPI and other insurance products (222,946 complaints) as well as general banking (80,067).
Behind Barclays on the most-complained-about list was Lloyds - the only bank in the top five to see complaints rise from the first half of 2013.
Between July and December, there were 256,656 complaints about the bank, which separated from TSB in September - an increase of 1% compared to the previous period. MBNA, Bank of Scotland and NatWest made up the rest of the top five.
However, across the board, the number of complaints made regarding financial services companies fell by 15% between July and December 2013, to 2,479,029 - which was down from 2,911,154 in the previous six months.
Putting customers first
Martin Wheatley, FCA chief executive, said: "No firm wants to top this particular list and they all should be striving to ensure that customers are being treated fairly and not given cause to complain. This is an indication that firms seem to be putting customers at the heart of their business, however, there is clearly more for us all to do to show consumers their interests come first."
Overall, the most problematic area of business for customers related to PPI mis-selling.
However, while there were almost 1.4 million complaints in the second half of the year, the figure had fallen by more than a fifth (22%) since the first half of 2013.
The FCA added that 94% of the £2.65 billion compensation paid out by financial services companies in the second half of 2013 was for insurance products, including PPI. Moreover, that compensation bill was up from £2.55 billion six months earlier.
Ashok Vaswani, chief executive of retail and business banking at Barclays, said: "We take all complaints seriously and endeavour to make sure that along with finding the immediate resolution, we tackle the root cause of the complaint head on to prevent other customers from being affected," he said.
"Every part of the bank is working to the same goal: to go out of our way to put things right and make our customers' experience seamless."
He admitted that there was still "a way to go" in reducing the number of complaints.