The Department of Finance's three-year overview of Ireland's economic prospects would have been under preparation for a month before the general election, the Labour leader, Mr Ruairí Quinn, has said.
Speaking as a former minister for finance, Mr Quinn said Mr McCreevy, "would have been kept in touch with the process and probably shown drafts".
The memorandum "reflects an unprecedented act of duplicity" by Mr McCreevy. "No weasel words from him or his Cabinet colleagues will absolve him from responsibility for the massive con-job he perpetrated on the Irish people.
"In any other western democracy, a minister who was guilty of such duplicity would have resigned by now or, failing that, would have been dismissed from office. But the one thing that we have never been able to expect from this Taoiseach is that he will uphold high standards in public office. He always turns a blind eye," said Mr Quinn.
In any event, Mr Ahern must share responsibility with Mr McCreevy, particularly in the wake of last month's Earth Summit when he lectured rich countries about their aid budgets.
There Mr Ahern pledged that there would be no retreat from the Government's promise to increase its overseas aid budget to 0.7 per cent of GNP by 2007.
He did this "knowing that Minister McCreevy had already decided to effectively freeze ODA payments over the next two years, rendering the 2007 target virtually unachievable".
Meanwhile, Labour's deputy leader, Mr Brendan Howlin, who is bidding to take over from Mr Quinn as Labour leader next month, said the cutbacks illustrated by the memo were "only the tip of the iceberg".
Describing the last election as the "most dishonest in history", Mr Howlin said: "A government elected on a platform of lies and deceit is a government without a shred of moral authority."
He said the Special Savings Incentive Accounts (SSIAs) could yet cost the Exchequer over €800 million a year if people increase their monthly contributions to the maximum.
Last year, he said Mr McCreevy had told the Dáil that he believed the annual cost would be about £127 million, though he now concedes that the full cost this year would be €517 million.
Meanwhile, Fine Gael's deputy leader and spokesperson for finance, Mr Richard Bruton, claimed that the Government was trying to "park the blame for the mess they made of the economy at the door of opposition parties".
" In the wake of the leaked document, Government Ministers are lashing out at any moving target in an attempt to divert attention from the mess they have made of public finances. They have been caught red-handed but still continue to shift the blame. It is grossly unfair to criticise Fine Gael's spending pledges in our Programme for Government when it relied heavily on the Government's own budgetary figures."