Banking misconduct has sparked an increase in complaints to a record high as a huge insurance mis-selling scandal continues to weigh on the industry.
The Financial Ombudsman Service (FOS), which settles disputes between consumers and financial firms, said new complaints rose 15% to 327,035 between January and June on the prior six months.
That was driven by a 26% hike in complaints about payment protection insurance (PPI), where people were charged for loan insurance which they did not need or could not claim on.
The ombudsman said some lenders continue to drag their heels on repaying mis-sold PPI, causing "long waits and unnecessary delays" for customers.
Complaints about Lloyds Banking Group were almost five times higher than a year earlier, at 129,293. They also rose 38% on the prior six months to make the part-nationalised lender the most complained-about group.
Complaints about PPI made up more than eight in 10 of those received by the ombudsman, with new PPI complaints hitting 266,228.
FOS chief executive Natalie Ceeney said: "Disappointingly we are still seeing cases where businesses are not following our long-standing approach to PPI, resulting in long waits and unnecessary delays for consumers.
"But, more positively, we are seeing encouraging signs from some major businesses that are starting to recognise the value of getting things right for their customers - with an increased focus on sorting out problems and concerns as quickly as possible."
The banking industry has so far set aside more than £18 billion to cover the cost of PPI - more than double the cost of the Olympic Games.
The insurance was supposed to step in when someone was made redundant or unable to work because of an accident or illness, protecting payments on mortgages, personal loans and credit card borrowing.
But millions were sold PPI they did not need, could not claim on, or were pressured into buying. In some cases, people who were self-employed or had pre-existing medical conditions were sold PPI despite being unable to claim.
Excluding PPI, complaints dropped 15% to 60,807 on the prior six months, including a 22% fall in banking complaints.
Customers typically complain directly to an institution before then appealing to the ombudsman if they are still unhappy.
The FOS upheld 80% of complaints against Bank of Scotland, owned by Lloyds, while 86% of complaints against sister firm Lloyds TSB were also upheld in customers' favour.
Lloyds was fined £4.3 million in February by the Financial Services Authority for delaying PPI compensation to 140,000 customers.
Lloyds released separate figures showing complaints it received fell 36% to 548,403 in the first half on a year earlier - including a 39% drop in PPI complaints.
Barclays was the second-most complained about group, with 44,223 cases lodged with the ombudsman, up 81% on a year earlier.
It was followed by Royal Bank of Scotland, responsible for 22,940 complaints to the FOS, and HSBC, which saw 18,444 complaints lodged with the regulator.