Redress paid to customers complaining about the sale of payment protection insurance neared £2 billion in 2011.
Which? has long campaigned against the sale of PPI on credit products.
Richard Lloyd at Which?, says, "It is good to see the PPI payout is finally starting to speed up but last year's compensation of nearly £2 billion is less than a quarter of what lenders expected to refund. Too many people are still finding the claims process too lengthy, the banks must streamline the process to make it easier for people to claim.”