NAB's Clydesdale Bank subsidiary in Britain "provided false information to the Financial Ombudsman Service in response to requests for evidence of the records Clydesdale held on payment protection insurance policies sold to individual customers," the Financial Conduct Authority said this week.
The FCA said it fined the bank £20.7 million for this conduct.
It is hard to frame this loss in the context of Clydesdale's profits, as it made losses in each of the last two years, including a loss before impairment expenses of £142 million in 2014.
"A team within Clydesdale's PPI complaint handling operation altered certain system print outs (in a small number of cases) to make it look as if Clydesdale held no relevant documents and deleted all PPI information from a separate print out listing the products sold to the customer," the FCA said.
It also said "these practices were not known to or authorised by Clydesdale's PPI leadership team or more senior management."
As a result of Clydesdale's conduct, of the 126,600 PPI complaints decided between May 2011 and July 2013, up to 42,200 may have been rejected unfairly and up to 50,900 upheld complaints may have resulted in inadequate redress for customers, the FCA said.
The regulator also said Clydesdale "agreed to settle at an early stage of the FCA's investigation and therefore qualified for at 30 per cent 'stage 1 discount'. Were it not for this the FCA would have imposed a financial penalty of £29.5 million."