Using the BIS's measure of "offshore deposits" – cash held outside the depositor's home country – and scaling it up according to the proportion of their portfolio large investors usually hold in cash, he estimates that between $21tn (£13tn) and $32tn (£20tn) in financial assets has been hidden from the world's tax authorities.
"These estimates reveal a staggering failure," says John Christensen of the Tax Justice Network. "Inequality is much, much worse than official statistics show, but politicians are still relying on trickle-down to transfer wealth to poorer people.
"This new data shows the exact opposite has happened: for three decades extraordinary wealth has been cascading into the offshore accounts of a tiny number of super-rich."
In total, 10 million individuals around the world hold assets offshore, according to Henry's analysis; but almost half of the minimum estimate of $21tn – $9.8tn – is owned by just 92,000 people. And that does not include the non-financial assets – art, yachts, mansions in Kensington – that many of the world's movers and shakers like to use as homes for their immense riches.
It seems this hurts poorer countries in particular. In many cases wealth hidden offshore exceeds the value of the debt such a country might have.
He corroborates his findings by using national accounts to assemble estimates of the cumulative capital flight from more than 130 low- to middle-income countries over almost 40 years, and the returns their wealthy owners are likely to have made from them.
In many cases, , the total worth of these assets far exceeds the value of the overseas debts of the countries they came from.
The struggles of the authorities in Egypt to recover the vast sums hidden abroad by Hosni Mubarak, his family and other cronies during his many years in power have provided a striking recent example of the fact that kleptocratic rulers can use their time to amass immense fortunes while many of their citizens are trapped in poverty.
The world's poorest countries, particularly in sub-Saharan Africa, have fought long and hard in recent years to receive debt forgiveness from the international community; but this research suggests that in many cases, if they had been able to draw their richest citizens into the tax net, they could have avoided being dragged into indebtedness in the first place. Oil-rich Nigeria has seen more than $300bn spirited away since 1970, for example, while Ivory Coast has lost $141bn.
Assuming that super-rich investors earn a relatively modest 3% a year on their $21tn, taxing that vast wall of money at 30% would generate a very useful $189bn a year – more than rich economies spend on aid to the rest of the world.