Royal Bank of Scotland has warned of a further £900million hit after being inundated with PPI complaints at the last minute.
The part-nationalised bank said compensation payouts are likely to leave it millions more out of pocket than anticipated - with the charge likely to be taken from its third-quarter results.
It comes on top of the £5.3 billion in provisions already set aside by the bank.
RBS said the number of claims last month was "significantly higher than expected", with a spike in the final days before the August 29 deadline.
The lender was also forced to extend its complaints form after the website crashed in the 48-hours to deadline day.
RBS customers who were unable to make a claim for PPI on Thursday are now still able to put in a refund claim, despite the official cut off date being just under a week ago.
The lender told Mirror Money that it will be accepting late claims due to a technical glitch in the 48 hours before the Financial Conduct Authority's final deadline.
It said anyone that faced a broken link when trying to make a new claim online will be able to do so now, using its extenuating circumstances form online.
A NatWest and RBS spokesperson said: "Any customer who could not make a PPI complaint due to technical issues earlier in the week can get in touch using the ‘exceptional circumstances’ process on our website."
It follows in the footsteps of Santander, which was forced to extend its deadline by a day, also due to technical errors.
