The "super-rich elite" are hiding more than $21 trillion US in tax havens around the world, an amount roughly equal to the combined GDP of the United States and Japan, according to a new report.

Commissioned by the Tax Justice Network, an independent British organization, the report is said to be the most comprehensive ever done concerning what it calls the "offshore economy."

Researched and written by James Henry, an expert on tax havens, the report states the hidden money could be as large as $32 trillion, and represents a massive black hole in the world's economy.

The amount of tax income lost "is large enough to make a significant difference to the finances of many countries," Henry noted.

Hidden money from elites living in developing countries is "enough to make a significant difference to the finances of many countries... that are now struggling to replace lost aid dollars and pay for climate change. Indeed, once we take these hidden offshore assets and the earnings they produce, 'debtor countries' are in fact revealed to be wealthy," he said.

The report says:

UBS, Credit Suisse and Goldman Sachs are the three private banks handling the most assets offshore

92,000 people, or 0.001 per cent of the world’s population, hold $21 trillion in hidden assets

Henry, who collected data from the International Monetary Fund (IMF), the World Bank and the Bank of International Settlements, said the figure he came up with is conservative because it doesn’t take into account property like yachts or other physical assets.

"These estimates reveal a staggering failure: inequality is much, much worse than official statistics show, but politicians are still relying on trickle-down to transfer wealth to poorer people," said John Christensen of the Tax Justice Network.