One of the best tax-avoidance tactics in the late Roman Empire was to sell yourself into slavery. You didn't really have to work as somebody's slave, of course - it was more like rock star Hotblack Desiato being "dead for a year for tax reasons" in Douglas Adams' wondrous confection The Hitch-Hiker's Guide to the Galaxy - but with the legal status of slave, you were exempt from taxation.
Nowadays, the legal manipulations used to avoid taxation are less dramatic, but they are spectacularly effective.
James Henry, former chief economist at business consultancy McKinsey and a member of the board of directors of the Tax Justice Network, has just published a report, "The Price of Offshore Revisited", that estimates the amount of wealth hidden in tax havens by the super-rich at a minimum of $US21 trillion: i.e. $21,000,000,000,000.
It might be as much as $US32 trillion, he adds, but greater precision is impossible when the whole point of holding money overseas is to keep it secret. Mr Henry came up with this range of numbers by sifting through data from the Bank for International Settlements, the International Monetary Fund, the World Bank, and private sector analysts - and it does not even include yachts, mansions, art works and other forms of wealth held overseas.
It doesn't matter. The point is that it's a very large amount of money: equal to the annual gross domestic product of both the United States and Japan. Some of it is the laundered proceeds of crime, and much was stolen from national budgets by corrupt national elites (an estimated $US306 billion from Nigeria, $US798 billion from Russia, $US1189 billion from China), but most is deposited by the West's respectable super-rich.
Mr Henry's report, published in The Observer last weekend, calculates that almost half the minimum estimate of $US21 trillion is owned by just 92,000 people, some of whom pay no tax at all. A number of very small places (Liechtenstein, Cayman Islands, Jersey) and a few larger countries like Switzerland make a good living by providing these secret tax shelters, and work very hard to protect their clients from exposure.
Back home, the "high net-worth individuals" also enjoyed the services of "a highly paid, industrious bevy of professional enablers in the private banking, legal, accounting, and investment industries," said Henry. We always sort of knew about it; now we know the scale.
Information of this sort is dangerous. It annoys those who merely work for a salary or an hourly wage, and whose taxes have to fill the gap created by the defection of the super-rich. It might even destabilise the established social order. But the British Government, at least, knows how to deal with that sort of thing.
Less than 48 hours after Mr Henry's revelations, British politician David Gauke, one of the Treasury ministers, went public with the assertion the lower orders cheat on their taxes just as much as the rich.
"Getting a discount with your plumber by paying cash in hand is something that is a big cost to the Revenue and means others must pay more in tax," he said.
But it's clear enough to ordinary people that ultra-rich people who avoid taxes on vast sums of money by employing expensive experts to hide their wealth overseas fall into a different category from the electrician who wants to be paid in cash. And hard-pressed governments, desperate for more revenue, are beginning to go after the tax havens.
Britain has made a deal with the Swiss authorities in which UK residents with undeclared assets in Swiss banks can make a one-off payment to the British Treasury of between 21% and 41% on their total assets, clear the slate, and remain anonymous.
The Swiss will then levy a withholding tax of 27% to 48% on future money going into those accounts, which will also go to Britain.
Germany has negotiated a similar deal, although it is still awaiting ratification by the Bundestag (parliament). The US Government has taken a different tack, demanding that Swiss banks hand over information on thousands of undeclared accounts held by American citizens. The heat is definitely on.
Yet while all this was going on, the amount of wealth managed by the top 10 private banks, most of it held overseas in secret accounts, has more than doubled in the past five years.
• Gwynne Dyer is an independent London journalist.
