The world's wealthiest individuals have stashed $21-trillion worth of assets in offshore tax havens, equivalent to the combined GDPs of the United States and Japan, a tax-transparency report said on Sunday.
The report commissioned by campaign group Tax Justice Network drew data from a wide range of sources including the Bank of International Settlements and the International Monetary Fund.
Report author James Henry, former chief economist at consultancy McKinsey, said that the headline figure was conservative, adding that up to $32 trillion may have found its way into havens such as the Cayman Islands and Switzerland.
According to Henry, these assets are "protected by a highly paid, industrious bevy of professional enablers in the private banking, legal, accounting and investment industries taking advantage of the increasingly borderless, frictionless global economy".
The report found that the top 10 private banks managed more than $6 trillion in 2010, up from $2.3 trillion five years earlier.
Tax expert and British government adviser John Whiting said he was doubtful of the figure.
"There clearly are some significant amounts hidden away, but if it really is that size what is being done with it all?" he asked.
The Tax Justice Network campaigns for tax transparency and against tax havens.