Warren Buffett is a famously shrewd investor with an eye for a bargain. So when, in late 2007, he saw equity indices plummeting in the wake of the credit crunch, he piled in.

Buffett has since sold $37.1bn (€29.6bn) of insurance on equity indices around the world, through his company Berkshire Hathaway, betting their value would go up in 15 to 20 years. He may now be wishing he had heeded his own advice about derivatives being "financial weapons of mass destruction" as the market has moved rapidly against him, stinging his company to the tune of $10bn, according to Berkshire Hathaway's results published last week.