A new study (PDF) has found that the world’s wealthiest individuals are holding at least $21 trillion in off-shore tax havens.

That’s equivalent to the gross domestic product of the United States and Japan combined.

The report, by a campaign group called the Tax Justice Network, says the three private banks handling the most offshore assets for the global super-rich are UBS, Credit Suisse and Goldman Sachs.

Britain said Wednesday it would toughen up oversight of tax avoidance schemes. This could see the government naming those who try to aggressively reduce their tax bills.

Tax avoidance is not illegal, but Prime Minister David Cameron, says it’s “morally wrong”. The crime is tax evasion. The British government hopes wealthy individuals will be forced into paying a fairer share.

Anchor Aaron Schachter speaks with London-based business reporter, Tim Jenkins.