So how did they do it? High earners have always engaged in "tax planning" to minimise their tax bills, but the revelation that 11 millionaires managed to pay no tax at all in 2001 is still extraordinary, writes Cliff Taylor, Economics Editor
And there's more. A total of 242 people with earnings from €100,000 to €1 million also had a zero tax rate for 2001, and a further 149 single people and married couples paid an effective rate of 20 per cent or less.
The news will cause huge irritation to the PAYE sector, who can - at best - modestly reduce their bills through write-offs for expenses such as VHI, mortgage payments and pension contributions, but still see a substantial whack of their incomes disappear before they even see it.
There are two main ways for a millionaire to have a zero - or negligible - tax bill. The first is to become a rock star or famous writer. Under the 1997 Artists' Exemption Scheme, those engaged in producing "original and creative" works judged to have "cultural or artistic merit" pay no tax on the sale of their works. They would of course still pay tax on other earnings - for example, rental income on property in which they invested, or dividend income from shares.
However, few enough of us have extraordinary artistic talent, and a relatively small group of those who do become millionaires. Nor do a large number benefit from other special tax-free allowances. One of these is an allowance on stallion income, from which a small number benefit significantly.
So the main way the super-rich avoid paying income tax is through the use of a range of tax allowances associated with property investment.
Here a Revenue report published in 2003, but covering the 1999/2000 tax year, gives us a clear pointer. This study was slightly different from that made available to the Labour front bencher Ms Joan Burton for 2001, but it points in a similar direction.
An examination of 400 top earners showed 117 of these had an effective tax rate of 30 per cent or less. Of these, 29 had a zero rate and a further 22 paid less than 5 per cent.
By far the most prevalent of the allowances availed of were those attached to property schemes, which give taxpayers substantial write-offs for investing in schemes such as multi-story car parks, hotels and other property- based capital allowances.
These schemes generally allow those who avail of them to reduce their tax bill by writing off their investment against tax over a period of years.
In the past, investors could in many cases use the tax relief gained through these schemes to reduce taxable income, no matter where such income came from.
In 1998 a significant tightening up in the Finance Act greatly restricted the use of many allowances for schemes commenced after that date. However, in 2001 many of the super rich were still benefiting from investments put in place before 1998.
For example, an investor who paid €5 million for a share of an IFSC building in 1996 would have been able to reduce his or her taxable income by €2.5 million in that year, and by €200,000 a year in each of the subsequent 12 years. Similar allowances were availed of by those who invested in hotels where the relief is spread over seven years.
The tightening up of the use of allowances, which began in 1998, has continued.
Under the old schemes, the key point is that the tax allowances available could be used to reduce taxable income, no matter where the income was earned.
So, for example, if a professional invested in the IFSC building mentioned above, he could have used the resulting allowances to reduce the amount of income earned from his profession on which he would have had to pay tax.
Now, under the vast bulk of property schemes, tax allowances can only be used to reduce rental income and only a small amount can be offset against other income. So such investments are still of value as tax shelters - particularly for those with a lot of rental income - but the ability to "shelter" large tracts of income earned from a profession is now very limited.
However, for those who got in before the restrictions came into place, the shelters will be of benefit for some years to come - in some cases for as long as 25 years, but in many cases for six or seven years.
In the 2003 budget, the minister, Mr McCreevy, cut the capital allowance on hotel investment. He also announced that many of the property-based schemes would end altogether at the end of this year.
But after strenuous lobbying from the building sector, this was extended in the 2004 Budget to July 31st, 2006.
The thinking behind these allowance schemes was that taxpayers would take the risk of investing in particular areas which would be an advantage for the economy. In return they would get tax relief.
One tax adviser argued yesterday that the rich were only availing of schemes put in place by the Government and that often the risk was considerable. "If you built a car park and nobody came to park in it, then you would lose much of your original capital."
Arguably, some of the schemes have achieved their goals, as evidenced by the development of certain designated urban areas and specific developments such as the IFSC. However, many have emerged as very significant tax shelters, allowing the rich to substantially reduce their tax bills.
And many of the allowances have been used by tax advisers as the basis for complicated tax schemes offering relief in ways not originally intended, and providing little benefit to the economy.
Despite the restrictions introduced in recent Finance Acts, Mr McCreevy, as minister, had to continually move to close off specific tax shelters that often used complicated structures. The relief on film investment has been overhauled, and the Revenue is believed to be closely monitoring other abuses, such as the artificial inflation by taxpayers of the amount they invest in qualifying schemes.
Will the combination of the tightening up of reliefs and their abolition in 2006, together with a more active Revenue approach to monitoring higher earners, mean the problem of super-rich tax evasion finally disappears?
Only a tax study in a few years time will answer the question.
Government officials, in the run-up to the 2004 Budget, examined the idea of a minimum income tax rate - probably in the 10 per cent to 20 per cent range - which would help to ensure that everyone paid a reasonable amount of tax.
They concluded that such a scheme would require a very complex piece of legislation. They also concluded that by setting a minimum acceptable tax rate, some who now pay a higher rate "might see such a rate as a target to be attained and reduce their tax payments to this target level".
This was seen as crucial, because in 1999/2000, 79 per cent of high earners were already paying a higher than 20 per cent rate. So a gradual chipping away at the reliefs, and a more active approach by Revenue are set to be the main weapons in a battle to ensure the rich pay their fair share.
