Barclays fine: 'It's about 10 days profit'
28 June 2012 Last updated at 10:37 BST
Barclays bank has been fined £290m for lying about lending rates to manipulate the market.
It could have affected trillions of pounds in transactions, including the price of mortgages.
Paul Lewis from Radio 4's Money Box programme looks at what manipulating interest rates means for anyone with a loan.