Barclays recorded the first drop in customer complaints in two years in the second half of 2012 - but it said that dissatisfaction levels are still "too high".
The bank said that overall complaints, including those related to payment protection insurance (PPI), were down by 6% in the second half of 2012 compared with the first half to 427,334, showing the first six-monthly drop in complaints for two years.
Within this figure, banking complaints fell by almost a quarter (23%) on the previous half year, with 121,115 cases recorded in the second half of 2012.
But Barclays conceded that PPI complaints are a "significant exception" to the progress it has made to drive down the number of customer gripes. Some 294,814 insurance-related complaints were opened in the second half of 2012, of which the vast majority relate to PPI.
This is more than double the number of complaints in this category compared with the same period in 2011 and also represents a 3% rise on the first half of 2012.
Barclays said it is continuing to treat PPI cases as a "top priority" and is proactively contacting customers, in a move which it expects will result in a further increase to PPI complaints levels in the first half of 2013.
The bank recently scrapped its product sales targets and from December its bonuses to branch and call-centre staff are based wholly on customer satisfaction.
Ashok Vaswani, chief executive of Barclays Retail and Business Banking, said: "Complaint volumes are still too high and we can't be complacent. One unhappy customer is one too many, and we still have work to do. Our sole focus is on helping our customers and getting it right so they don't feel the need to complain in the first place.
"This is why we have been investing in new products and services such as family springboard mortgages, mobile banking and free wifi in branches, and at the same time incentivising our frontline staff purely on the level of service they provide to our customers."
Barclays said that if PPI were removed from its figures, complaints would have dropped by more than a fifth on the first half of 2012.