Banks' handling of payment protection insurance compensation claims are to be investigated by the financial watchdog which said it is considering a new consumer publicity campaign linked with a time-limit on complaints.
Since January 2011, more than 14 million consumer complaints about the sale of PPI have been handled with £17.3bn compensation handed over. The total bill for the scandal could top £24bn.
But there has been continued criticism of banks' delaying tactics and failure to fine those affected by the UK's biggest-ever financial mis-selling scandal.
Last year, the Financial Conduct Authority revealed that banks, credit card providers and personal loan companies had agreed to reassess more than 2.5 million complaints during 2012 and 2013, which they may have either "unfairly rejected or paid too little redress to".
Meanwhile, more than five million customers identified as being at high risk of having been mis-sold but who have not complained are being sent letters by the banks.
The FCA said it will begin its investigation shortly and report on the evidence in the summer.
It warned that it may make "further interventions" such as a consumer communication campaign, a possible time limit on complaints, or other rule changes.
Consumer groups are likely to fight a time-limit.