Of all the stains on the reputation of UK banks, the PPI scandal is surely the most shameful, the most revealing of low human behaviour and the one with the most far-reaching consequences. Between 1990 and 2010, some 30 million customers were sold Payment Protection Insurance, supposedly designed to cover them if they became unable to make debt repayments; no one knows what proportion of those policies were ‘mis-sold’, but compensation has so far amounted to more than £36 billion, plus £12 billion of admin costs for the banks.