Gillian Guy, chief executive of Citizens Advice, said: “Unscrupulous claims management companies have preyed on victims of the PPI scandal. It’s bad enough banks let consumers down over PPI, but the fact some claims companies were able to swoop in and unfairly siphon off compensation adds insult to injury.

“Our evidence shows up to 39% of customers did not know they could make a claim without these firms. It’s crucial free, independent advice is available for anyone caught up in PPI so that they can seek compensation without the need to pay fees.

“We would also like to see the Claims Management Regulator continue to take enforcement action against firms that  are shown to be operating outside the rules.”