It could take up to a year for some PPI claims to be resolved, despite the regulated eight week deadline, Which? has found.
The Financial Conduct Authority (FCA), the UK finance regulator, told us the delay is a result of an 'unprecedented response' to its PPI complaints campaign.
In the run up to the 29 August claim deadline, the FCA was urging consumers to 'jog their memories' back to the 1990s and 2000s, when they may have been mis-sold PPI.
But it said many banks and other PPI providers were overwhelmed by the sheer volume of last-minute claims.
As a result, some banks have informed the FCA there will be delays, despite having had two years to prepare.
It is likely many claims will take longer than the statutory limit of eight weeks for banks to resolve.
But the FCA has said anyone with an outstanding claim will get the decision they're entitled to as soon as possible.
The regulator said it is challenging firms to deal with these complaints as quickly as is reasonable, given the large volumes.
'It will take time for some consumers to receive their response, but it is important to us that these complaints are handled fairly and accurately,' an FCA spokesperson said.
At Which? there were more claims submitted via our free PPI claims tool in the final fortnight before the deadline than we'd typically see in an entire year.
Many of those have now told us that their banks have warned them about delays with their claim.
We asked several major banks about their progress with the current claims process.
HSBC, Santander, Lloyds, RBS and Nationwide all told us they received large numbers of PPI complaints in the run up to the deadline.
All of them wanted to reassure customers that they would be resolving cases 'as soon as possible,' and will be getting in touch with anyone who's complaint will not be resolved by the eight-week deadline.
Nationwide added that it is committed to working through claims quickly and 'will calculate any compensatory interest that is due to include the time it's taken to review each case.'
But the FOS says it understands banks are receiving an extremely high volume of PPI refund enquiries, and has urged anyone who submitted their claim in July or August to hold off making a complaint until they've heard from their bank.
It also told Which? it expects banks to prioritise cases where a claimant is vulnerable or in financial hardship.
Banks and regulators agreed to a 29 August 2019 mis-sold payment protection insurance claim deadline.
The financial regulators' own rules require banks to provide a final response within eight weeks of a complaint being received.
That means all PPI claimants should have a response by 24 October.
But due to the volume of last-minute claims, these timelines are no longer feasible and a 'reasonable delay' is expected.
Other banks and online claims websites struggled under the weight of demand around the deadline.
Santander had to accept claims beyond the official deadline and up until 8pm the following day because of a website glitch that it blamed on the onslaught of last-minute claims.
The deadline for submitting a mis-sold PPI claim to your bank or financial provider was agreed by the banks and financial regulator and came into effect at 11.59pm on 29 August 2019.
You can still make a PPI claim if you've experienced exceptional circumstances that prevented you from making a claim before the deadline, but this will be assessed on a case-by-case basis. Head to our for more information.