Barclays was the most complained about bank in the second six months of 2011, figures from the Financial Ombudsman Service (FOS) showed.
Between 1 July and 31 December the ombudsman dealt with a total of 11,524 complaints about the bank, finding in the favour of customers in 84% of them. Of these cases 6,975 were about the bank's sales of payment protection insurance (PPI), policies sold alongside loans and credit cards that promised to pay out in the event of illness or redundancy but were sold to many people who were unable to make a claim.
A further 3,474 were about banking and credit, while the remainder covered subjects from mortgages to investments.
However, Lloyds was the most complained about banking group over the six-month period, registering 20,310 complaints, against Barclays group's 12,273, and complaints were down by a third across the board.
A total of 106,193 new complaints were made to the ombudsman – down from almost 150,000 during the previous six months. Over half were about just five financial services companies of the 100,000 businesses the scheme covers.
PPI was the product at the centre of 46,700 cases. This was a 53% decrease on the number received in the first six months of the year, but the ombudsman is currently receiving around 1,000 cases a day, and the ombudsman said the number was likely to grow.
The main driver for the fall was the decision by the Financial Services Authority (FSA) to extend the time big firms had to deal with mis-selling complaints around PPI, but as of January the time period has been moved back to eight weeks. As a result, the ombudsman said it expected to receive a record 165,000 PPI complaints in 2012/2013.
Complaints about mortgages were up by 38% on the first half of the year, accounting for 5,202 cases. A spokeswoman said that although customers were complaining about the day-to-day running of their mortgages, the underlying problems tended to be financial hardship.
The data shows that in the second half of 2011 the ombudsman service upheld an average of 72% of complaints in favour of consumers, compared to 47% in the first half of 2011 – reflecting the impact of PPI cases.
Natalie Ceeney, chief executive and chief ombudsman, said: "The proportion of complaints that we have upheld in favour of the consumer – ranging from 6% to 100% – clearly highlights the difference in PPI complaints handling across major businesses over this period.
"It also reflects the efforts made by some businesses to resolve quickly the hundreds of thousands of PPI complaints that had built up during the banks' unsuccessful PPI legal challenge. We now hope to see all businesses who were involved in PPI mis-selling resolving their customer's complaints fairly, properly and quickly."
Antony Jenkins, chief executive of Barclays Retail and Business Banking said tackling complaints was the bank's top priority: "Today's figures show a 36% reduction in new FOS cases. This follows our 30% year-on-year reduction in FSA-reportable banking complaints, and confirms that our actions are delivering results for customers.
"We can and will do more to improve service and go further and faster to drive down complaints. We are aiming for further significant reductions in underlying complaints in the first half of 2012 as we continue on our journey to get it right first time, every time, for our customers," he said.
Recently the ombudsman warned that consumers were still needlessly using claims management companies to handle their problems with PPI and collectively losing millions of pounds as a result.