The convincing Yes vote in the Nice Treaty referendum has cleared the way for next Thursday's European Council meeting to approve the accession of 10 new member-states in 2004.
"We can now ratify the Treaty of Nice and the truly historic enlargement of the European Union can go ahead", the Taoiseach, Mr Ahern, declared at Dublin Castle yesterday after the result was announced.
The treaty was approved by a majority of 62.89 per cent to 37.11 per cent after 18 months of preparation and an intensive campaign to reverse the June 2001 result. Then it was rejected by 53.87 per cent to 46.13 per cent.
Campaigners on all sides agreed yesterday the higher turnout this time was the key to the result. Some 49.47 per cent voted this time compared to just 34.79 per cent in June 2001. The increased turnout appears to have consisted almost entirely of Yes voters.
The result eases the political pressure on the Taoiseach after his most difficult period in power since becoming Taoiseach in 1997. A defeat would have brought the prospect of a challenge to his leadership closer amid considerable discontent in Fianna Fáil over the economy and the handling of the Flood tribunal report.
Mr Ahern yesterday paid tribute to the Opposition parties, trade unions, employers' groups and others who had campaigned for a Yes vote. The treaty was approved in all 42 Dáil constituencies.
However, campaigners against the treaty said the Yes vote was due to the weight and money the establishment put behind their campaign as well as what the Socialist Party's Mr Joe Higgins called the "overwhelming weight of Yes propaganda in the press".
The Taoiseach will now join the other 14 EU leaders in Brussels on Thursday, when they will formally approve the Commission's proposal that 10 new member-states join the EU in 2004.
The Danish Prime Minister, Mr Anders Fogh Rasmussen, whose country holds the EU Presidency, telephoned the Taoiseach yesterday afternoon to congratulate him on the result. Mr Ahern also had a half-hour telephone conversation with Mr Romano Prodi, the European Commission President, after the outcome became clear.
"I'm very, very happy about the results of the Irish referendum, it was a big challenge," Mr Prodi told a press conference in Paris yesterday. He said: "This referendum has given us a political green light. European unity is now assured. I am highly enthusiastic. The door is open for European unification."
Welcoming the result, the French President Jacques Chirac said: "It is essential that we all keep our eyes on the prize of a united Europe"
While the Taoiseach will be relieved that Ireland is no longer seen as an obstacle, other member-states now pose problems for the negotiations. Commission officials are cautious in their expectations of this week's summit and officials in EU capitals suggest that a deal is unlikely.
The 15 leaders will attempt to hammer out a deal on Thursday and Friday on how to pay for enlargement. The candidate countries see the current proposal on the phasing in of farm subsidies as miserly, while some EU member-states, led by Germany, believe it is too generous.
The collapse of the Dutch government last week has posed another problem. While the Dutch Prime Minister Mr Jan Peter Balkenende insists he has a mandate to negotiate at Brussels, the Dutch parliament recently passed a motion, with the support of all three outgoing government parties, stating that four of the candidate countries were not yet ready to join the EU.
The Danish Presidency believes that failure to agree a common position on financing enlargement will put almost unbearable pressure on December's summit in Copenhagen.
If a deal is reached and the accession treaties are approved, Poland, Hungary, the Czech Republic, Slovakia, Slovenia, Lithuania, Latvia, Estonia, Cyprus and Malta will join the EU in 2004, the year of Ireland's next EU Presidency.
The main Opposition parties declared last night that they would now resume full-blooded opposition to the Government. Fine Gael leader Mr Enda Kenny said his party would begin a campaign to "rout this treacherous Government". Labour Party leader Mr Ruairí Quinn said the Yes vote was not an endorsement of Government policies, and there was real anger at the deceitful election.