The number of complaints made against financial services firms jumped by 15% during the second half of 2010, with more than half settled in favour of consumers, new figures show.
The Financial Ombudsman Service received a total of 97,237 complaints during the six months to the end of December, up from 84,212 in the previous six months.
The increase was largely driven by the ongoing rise in the number of people complaining about controversial payment protection insurance, with cases relating to the product now accounting for more than half of the ombudsman's workload.
There was also a big increase in the number of disputes being upheld in favour of consumers, with the ombudsman finding against financial services firms in 53% of cases, up from 44% in the first half of the year.
Part-nationalised Lloyds Banking Group remained the most complained-about financial institution, receiving 22,181 complaints during the period - more than one in five of the total. However, this could reflect the fact that it is the UK's largest bank.
Royal Bank of Scotland, which also received a Government bail-out, had the second highest number of complaints at 8,644, a third more than during the first half of the year, followed by Barclays at 8,256.
HSBC saw the number of complaints it received more than double to 8,238, while Santander also saw a significant increase in disputes referred to the ombudsman, with these rising by 26% to 6,759.
Overall, these five banks accounted for more than half of all the complaints the ombudsman received.
The level of complaints which were settled in favour of consumers by different firms ranged from just 5% to 95% for Eisis, which sells insurance.
Chief ombudsman Natalie Ceeney said: "The latest set of complaints data continues to show that, while some financial businesses are improving the way they handle their customers' complaints, some regrettably are not."