The former Taoiseach, Mr John Bruton, has accused the Government of endangering Ireland's national interest by undermining the Convention on the Future of Europe.
He revealed the Government has not once asked him to raise any issue in his role as a member of the Convention's powerful Praesidium and has never asked for a briefing about its activities.
"The Irish Government is taking an absolutely passive approach to the Convention. It is a recipe for ensuring that Ireland is completely isolated in Europe," he said.
Speaking in Brussels this week, the Minister for Foreign Affairs, Mr Cowen, played down the importance of the Convention, which will draft a constitutional treaty for the EU.
He stressed that, regardless of the Convention's outcome, heads of government will have the final say in an Inter-Governmental Conference (IGC).
"I wouldn't be a bit surprised at what comes out of the Convention. The political decisions will be made in the IGC process," he said.
Describing the Minister's remarks as "simply wrong", Mr Bruton accused Mr Cowen of undermining the Convention and the work of the Irish representatives there.
"We are politicians, representing in my case the Dáil, in Dick Roche's case, the Government. The Convention is seen by all the other governments as a body where political decisions will be made. If Mr Cowen is right and they are wrong, I must ask myself if I am wasting my time," Mr Bruton said.
Mr Bruton praised the work of the Department of Foreign Affairs and the contributions of Mr Roche and the other Irish representatives at the Convention. But he said it had been clear for some time that the Government was not taking the process seriously enough.
Mr Bruton will raise his concerns about the Government's attitude at a meeting with the Taoiseach next week. He is meeting the Convention's president, Mr Valery Giscard d'Estaing, today to discuss recent remarks by Mr Giscard suggesting that member-states might have to leave the EU if they decline to sign up to the new treaty.
Mr Bruton's remarks came after it emerged that Ireland has been excluded from an initiative to promote the interests of smaller EU member-states at the Convention on the Future of Europe. The Republic was one of only three small member-states not to be invited to a dinner to discuss the initiative that was hosted in Brussels last Monday by the Dutch European Affairs Minister, Mr Atzo Nikolai.