"A customer borrowing £100 for 28 days without the consent of Santander would repay £200, for example.
That is the equivalent annualised percentage rate, or APR, of 819,100%.
Comparisons between banks and so-called payday lenders showed that the annualised percentage rate charged for borrowing £100 over 28 days varied from 969% to 819,100%.....
No payday loan lender charged an APR of more than 5,000% but two banks - Santander and Lloyds TSB - charged an equivalent APR of more than 300,000%.
Barclays would charge a customer using a personal reserve - a pre-agreed emergency borrowing facility - £22 for every five consecutive working days they were in it. This means customers would pay £88 on top of the £100 capital after 28 days - an equivalent APR of 366,000%."