European Trade Commissioner Peter Mandelson has said "completely fallacious assertions", about abortion, conscription and neutrality were made ahead of last week's referendum on the Lisbon Treaty.
"All of those fears should have been addressed, all those misrepresentations should have been corrected. Frankly, the untruths that were put out by some of the propagandists should have been rebutted right at the beginning of this campaign", Mandelson said.
"If you don't defuse it and demolish it instantly, it gets its skates on and it's around the country and everyone is assuming it's right before the other side get up on their soapbox."
Mr Mandelson said he did not believe the Irish people were rejecting Europe and defended the treaty as "absolutely essential".
He said "I think we're too defensive in Europe, in the Commission, amongst the member states - we are a bit defeatist."
"We seem to think that, if people are asking questions about Europe, it's because they are hostile - it may be just because they're asking questions."
Mr Mandelson was speaking ahead of today's EU summit, which is expected to be dominated by fall-out from the Irish vote.
With all 27 EU members required to endorse the treaty before it can take effect, the Irish rejection has put its future in doubt.
Mr Mandelson pointed to his experience as a campaigner for Britain's former prime minister Tony Blair, saying that if opposition arguments were not confronted swiftly, as in the Irish campaign, the political battle was more difficult.
"We used to operate on the maxim that speed kills. If you do not quickly, speedily rebut things that are said about you that are untrue, then they are going to stick and cause you harm and feed the opposition," Mr Mandelson said in Moscow, before talks with Russian ministers.
The former British minister brushed off personal criticism directed against him by the Irish farm lobby because of his negotiating tactics at World Trade talks.