Court rulings have found millions of people could make new PPI claims.
It has been discovered even those who were happy with their policies could get a cash payout - and it's all down to commission paid to banks by insurers.
Tens of millions of payment protection insurance policies were sold to many Brits over the years, but often unfairly against finance where it wasn't fit for purpose.
The payment insurance was frequently attached to loans, credit cards, car finance, mortgages and more - with many people shelling out unnecessarily.
People were told PPI would cover their debt payments if they died, become ill or disabled, lost their job or were left unable to repay debt for another reason.
But there were also a series of exclusions which meant it was sold to people who could never claim on it, while commissions and profits were high, reports the Mirror.
In 2008, the regulator stepped in after thousands of complaints from people who had been mis-sold.
As a result of malpractice, over the past ten years more than £35billion has been handed back in compensation to mis-sold customers as a result of payment protection insurance.
The payouts and refunds were due to end in August last year, with a deadline set for claims, but new rulings mean even more people could be eligible.
The new cases are based on the amount of commission paid to banks by insurers, but not disclosed to customers.
Commission made up more than 95% of the policy’s cost in the most serious cases, The Sunday Times reports.
This means that even if you weren't mis-sold the policy, or have already claimed, you could still get a payout.
Experts said recent claims made against banks could mean millions of new compensation claims, including from people who were denied payments, received only partial refunds or never claimed under the previous scheme.
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That's because under the old rules, customers only got back half the commission the bank was paid, and these new cases have seen judges award far more.
NatWest lost a case earlier this year - despite it being past the official claims deadline - when Karen Smith, 58, from Cornwall, received an unsolicited refund from the lender worth £529.80, representing "a refund of commission over 50% charged on the PPI premiums paid".
As she didn't know she was paying commission, she took NatWest to court and won £1,500.
Bodmin County Court District Judge Jonathan Stone said the bank "provided no information to Mrs Smith that would enable her to discern that it would be receiving commission", but it knew how much commission it would receive.
He added: "The inequality of knowledge was total and as a result, of course, the relationship was unfair."
NatWest is appealing against the decision.
A NatWest spokesman said: "This case is the subject of an appeal and so it would not be appropriate to comment further."
Martin Richardson, from solicitors MoneyPlus Legal, said new claims against the banks could amount to "billions of pounds".
