A demand was made for the Taoiseach to explain urgently why he amended the 1994 Finance Act when he was minister for finance.

Ms Roisin Shortall (Lab, Dublin North-West) claimed the introduction of Section 19 of the Act benefited one individual and prevented the Revenue Commissioners recovering up to £1.5 million.

She called on Mr Ahern to give a "full and frank" account of the "extraordinary circumstances" in which a prominent businessman and Fianna Fail donor, Mr Ken Rohan, benefited from this amendment. The section grants tax relief on art collections in historic houses which are open to the public.

However, the Minister for Finance, Mr McCreevy, said that the legislation applied generally. "It was not confined to a sole beneficiary, as has been claimed in the media."

Others in similar circumstances could benefit, "as could those who might, but for the relief provided by Section 19, have been liable to assessment to tax on the objects in question".

Ms Shortall said the Sunday Tribune had published new data which showed that the Revenue Commissioners could not pursue Mr Rohan for a tax assessment of £1.5 million because of the introduction of Section 19.

The Taoiseach "has attempted to pour water on the flames by claiming that Mr Rohan's tax assessment had already been brought before the Revenue Appeal Commissioners and that they found in favour of Mr Rohan.

"The claim by the Taoiseach is that Mr Rohan's tax bill was nil at the time the legislation was introduced and therefore any claims of impropriety or worse are unfounded."

She added, during a debate on the adjournment, that the Taoiseach failed to place on the public record that the Revenue Commissioners had intended to appeal the decision of the Appeal Commissioners to the High Court.

The Revenue Commissioners' efforts to recover the £1.5 million "were blocked by the introduction of Section 19." This section of the Finance Act "scuppered" the intention to mount a legal challenge.

The Labour TD said Mr McCreevy had claimed it was normal practice for the Revenue to appeal vigorously complex cases to the courts. However, she added, when a Fianna Fail donor was about to receive the same "vigorous" attention from the Revenue, "the law is changed, which prevents a legal challenge from the Revenue."

Outlining the history to the amendment, Mr McCreevy explained that the original representations were in February 1993 when the Irish Georgian Society said that some of its members were very concerned by what they believed was a new proposal by the Revenue Commissioners to tax art collections in the State.

At the same time the Department of Arts, Culture, Heritage and the Gaeltacht wrote to the Minister supporting the proposal and referring in particular to the case of a tax assessment on a named individual (Mr Rohan). Mr McCreevy said that the individual believed that there was a danger of persons moving works out of the State for sale if the tax were invoked. Bord Failte also supported the proposal.