"The institutional fate of 500 million Europeans is in the hands of 3 or 4 million Irish. It's a very undecided country," he said.

"We are faced with a world that is soon going to have more than 9 billion people. There is enormous work to do in the fields of energy, immigration, industry and social affairs and we're not going to stop. So we will find a solution if ever we are faced with this type of situation," he added, but refused to say whether there is actually a Plan B in the event of a No vote.

The French comments are further indication of the impatience felt by larger member states that a referendum in one small member state could derail the Lisbon Treaty completely.

Earlier this month, Italian leader Silvio Berlusconi also advocated the creation of a core of EU states that would push ahead with integration.

"If the Lisbon Treaty on EU reform does not pass, we need to completely revisit the current functioning of Europe to create a core of states that operate beyond unanimity," he said.

Recent polls indicate that the result will be a Yes on 2 October. The Ireland of this year is profoundly changed in comparison to when the first vote took place 16 months ago. The financial crisis has plunged the country into double-figure unemployment and it is facing a predicted decline in GDP of 9.8 percent this year. Analysts suggest that fears about jobs and economic security are likely to play towards a Yes vote.

But Brussels remains nervous about the outcome, with the No side fighting a vocal campaign focusing on many of the same issues that were raised ahead of the first vote.

A rejection would stop the treaty coming into force across the 27-nation Union as it needs to be ratified by all member states, meaning the country has become the focus of anti-treaty campaigners from across Europe.