Encouraging women back to the workforce by giving additional tax breaks to dual-earning couples was the most controversial part of the most contentious Budget of recent years.

The measure, individualisation as it is known, means spouses will not be able to claim each others' tax bands as has previously been the case. It means that tens of thousands of one-earner couples, who earn more than £28,000, would bring home less money than their dual-earning counterparts.

A debate has raged ever since the Budget speech about the equity of this proposal and, indeed, the Government's commitment to the family unit.

The measure stirred up unprecedented opposition from Fianna Fail TDs, many of whom took to the plinth at Leinster House in a display of agitation not even seen in the upheavals of the mid-1980s.

It seems certain that neither the Minister for Finance, Mr McCreevy, nor the Taoiseach, Mr Ahern, anticipated the furore. Indeed, Mr McCreevy has stated that with 20:20 hindsight he would not have gone ahead with it.

However, the documentation obtained by The Irish Times under the Freedom of Information Act shows that none of the politicians involved can say they were wrongfooted.

The Labour Party spokesman on finance Mr Derek McDowell said last night that the papers from the Tax Strategy Group demonstrated beyond all doubt that Mr McCreevy and Mr Ahern bear personal responsibility for the Budget debacle.

"It is clear that Mr McCreevy went on a solo run despite being warned of the implications of his proposals," he added.

The documents, which form part of the group's deliberation, show that top civil servants and political advisers warned against the individualisation proposal.

Just two weeks before the Budget, this group had long abandoned the idea and was looking at a proposal to spend around £700 million (€889 million) cutting the top and standard income tax rates by one percentage point each and using most of the remaining resources to widen the standard rate band to take people out of the top rate.

Instead, the politicians themselves appear to have chosen to go back to the old proposal and implement it without safeguards as well as doubling the recommended cuts in the rates, despite warnings that this too would benefit the better off disproportionately.