More than two million people have been mis-sold payment protection insurance (PPI) over the last five years, Which? has claimed.
This will bring PPI insurance marketing and sales under increased pressure, with a suspected one in three consumers unlikely to be able to make a claim.
Personal finance campaigner at Which?, Doug Taylor, remarked that he is "amazed"at the scale of the problem.
He said: "We've always known that people were being mis-sold PPI, but we were still amazed to discover the scale of it.
"It appears that salespeople are chasing their commissions, their bosses are chasing profits - where's the sense of responsibility to the customer."
Consumers may fall foul of exclusions found in policies and could potentially tarnish the reputation of the insurance marketing and sales sectors.