Lloyds Banking Group, the UK's largest bank, said its customer complaints rose by 14% in the second half of 2010.
Lloyds, which runs the Halifax and Bank of Scotland, received 330,000 complaints in the last six months of last year, writes the BBC.
The bank said the increase was due to the continued upsurge in complaints about the sale of payment protection insurance policies.
"We know we still have a lot to do," says Martin Dodd, the group's director of customer services.
He explained the statistics, to be published by the FSA at the end of March, were starting to reflect a thorough overhaul of complaints procedures at Lloyds.
Since last autumn, 40,000 branch and call-centre staff had been retrained to deal with complaints.
Dodd said these changes meant the bank was now resolving 90% of all new complaints being made against it.
Complaints on banking services at the group fell by 12% to 155,000.
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