The UK's financial watchdog cannot be sure that the mis-selling of financial products has stopped, despite despite the £22bn paid in compensation for the PPI mis-selling scandal, the National Audit Office has said.

The Payment Protection Insurance (PPI) mis-selling scandal was the most prominent mis-selling case ever in the UK but despite the Financial Conduct Authority's (FCA) crackdown on misconduct, the NAO has found no significant proof of a reduction of mis-selling activities.

Financial services companies involved in the PPI misconduct have paid a total of £22bn (€27bn, $30bn) in compensation to customers between April 2011 and November 2015. A further £298m ($413m, €377m) was paid out in fines between April 2013 and October 2015. Despite the high misconduct costs, Amyas Morse, head of the National Audit Office said that mis-selling "remains a major problem for Britain's consumers".

"Legislative restrictions limit my access to information that the FCA holds on firms making it impossible to draw definitive conclusions on its approach," Morse said. "The information my staff could see, such as customer complaints, does not show any clear reduction in the extent of mis-selling."

The FCA defines mis-selling as "a failure to deliver fair outcomes for consumers" when selling financial products.The NAO said that mis-selling accounted for well over half of financial services customer complaints in 2014, up from just a quarter in 2010. According to the report, published on Wednesday (24 February), customers are reluctant to put complaints forward to the national ombudsman, but it still received around 4.57 million complaints.

An FCA spokeswoman said in a statement that even the watchdog is unlikely to completely eliminate mis-selling. "Our aim is to avoid and minimise it as far as possible, create the right incentives and culture in firms and to ensure appropriate redress for consumers and regulatory penalties for poor conduct are put in place when it occurs," she said.

"The report makes clear that the recommendations, which we are accepting, are designed to build on the FCA's current strategy and increase confidence that it is achieving its intended outcomes for consumers. Protecting consumers from the effects of mis-selling is central to what we do."