Lloyds Bank was the most complained about financial group in 2011 with 20,310 complaints in the second half of the year.
This figure fell from 37,696 received by the Financial Ombudsman Service (FOS) in the first six months of the year, and the group says it's managed a reduction in complaints by 24% in the past year.
Although the Lloyds figures were significantly higher than those of any other financial institution, they do include complaints made about the rest of the group, including Halifax, Bank of Scotland, Scottish Widows and Cheltenham & Gloucester.
António Horta-Osório, chief executive of Lloyds, said: "I am pleased with the significant achievements we have made in reducing complaints in 2011. However, we need to keep improving and so we have set a new target for 2012 when we will aim to have no more than 1.3 complaints per 1,000 accounts."
Barclays followed in second place with 12,273 complaints, and MBNA and Royal Bank of Scotland were next with 9,903 and 6,553 complaints respectively.
Most of the complaints the Ombudsman received related to the mis-selling of payment protection insurance (PPI). The overall number of complaints to the FOS was down by 149,925 in the second half of the year as a result of the banks improving their handling of PPI cases.