Any attempt by the EU Commission to move forward with the Nice Treaty without formal Irish ratification would be illegal and subject to challenge in the European or Irish courts.

"Like it or lump it", the EU Commission has no option but to accept that the Irish had spoken on the Nice Treaty, according to Government backbencher Mr Dick Roche (FF, Wicklow). If the Commission ignored the vote, "they will do so at their peril".

During a debate on the Nice Treaty, Mr Roche was sharply critical of the EU Commission and its President, Mr Romano Prodi. He said they should accept the Irish vote "with more good grace than they have shown in the recent past".

It was "extraordinary" to hear Mr Prodi, who is visiting Ireland, refer to taxation issues. "High-tax, high-spend policies may well be suitable for certain member-states," Mr Roche said. "The only body constitutionally charged with raising taxes in this country is Dail Eireann."

The Nice Treaty, no matter what its good intentions, "is a document that has been democratically tested in only one member-state, and that is Ireland".

Mr Michael D. Higgins (Lab, Galway West) said it would be wrong to present the Nice result "as a problem that the Irish people represent. It is as if the Taoiseach goes to Gothenburg and other cities dragging after him the problematic Irish people."

He said people without a mandate were speaking about the future.

"Those with the mandate are not participating in the same debate. Thus the European Parliament tediously and slowly arrives at a particular opinion on the future of Europe, yet off-the-cuff remarks are made by those who are the appointed members of the Commission."

Mr Sean Haughey (FF, Dublin North Central) said he was sceptical of the Forum on Europe when he heard the Taoiseach say it would consist of the political parties and the social partners, because they recommended a Yes vote.

"We need to move beyond those groupings. We need to move beyond the cosy consensus and really engage with the people in an imaginative way with this forum.

"Unless we do that, the forum will be just another talking shop that will produce a report that probably nobody will read anyway."

He also said there should be no attempt to change the McKenna judgment and the Referendum Commission rules in advance of any new referendum. It "will be seen as us trying to change the rules in order to change the result".