The next phase in the Revenue drive to collect unpaid taxes hidden in bogus non-resident accounts could prove to be highly lucrative, offering the potential to gather millions of pounds for the Exchequer.

The Revenue has already collected £173 million in unpaid DIRT on those bogus accounts from the State's financial institutions and is now turning its attention to the accountholders.

As the DIRT on these accounts has been paid by the banks and building societies the Revenue is now chasing the source of the funds held in those accounts, whether it was undisclosed income or investment gains.

The account-holders, - expected to include a huge range of individuals from small shopkeepers to elderly people - are being invited to disclose whether this money should have been declared for income tax, PRSI, VAT, Capital Acquisitions Tax, Capital Gains or other taxes.

This will move the Revenue Commissioners closer to finally collecting the monies owed to the State arising out of widescale tax evasion in the 1980s and 1990s.

The £173 million it collected from the banks was on foot of a "look back" audit recommended by the Dail Public Accounts Committee after the DIRT inquiry. Some of the banks have written to the individual account-holders themselves to seek reimbursement for the DIRT payments made on their accounts.

The potential financial gain from this latest exercise could be quite substantial, although the Revenue has declined to estimate an amount.

In one case highlighted during the DIRT inquiry, an audit of the Bank of Ireland branch at Miltown Malbay, Co Clare in 1992 recovered £200,000 in unpaid DIRT arising from bogus non-resident accounts held there. But the Revenue subsequently netted a further £1.8 million by pursuing the account-holders for untaxed income.

The report following the DIRT inquiry was very critical of the banks and the Revenue Commissioners for allowing widescale DIRT tax evasion. AIB made the highest settlement with the Revenue, paying £90 million of the £173 million collected and claimed to have negotiated an amnesty with the Revenue on these accounts. The Revenue claimed it did not have the powers to investigate tax evasion facilitated by the banks but has since been given more extensive powers.