The UK's four big banks - Barclays, HSBC, Lloyds and RBS, have agreed to start work on reviewing individual sales and providing compensation, after City watchdog the FSA found a significant proportion of interest rate swaps were mis-sold to small businesses.
The cost of compensating businesses could total as much as £1.5 billion across the sector.
Barclays, HSBC and Royal Bank of Scotland have already set aside around £360 million to cover potential claims.
The City watchdog found that 90% of interest rate swaps sold to small businesses were mis-sold, and customers are entitled to compensation.
An FSA review found that more than 90% of so-called interest rate swaps sold to businesses were mis-sold. But what are they?