His words come despite a statement by the French prime minister Jean-Pierre Raffarin on Tuesday (24 May) saying that another referendum is "not a perspective that France could accept".

The Luxembourg leader went on to say: "And if, even after the European Council deals with the problem, we do not manage to find the right answer, the treaty will not come into force".

Mr Juncker stressed that a French No would be a "disaster" and excluded the possibility of imminent re-negotiations.

"The idea circulating in France that there could be an immediate re-negotiation (of the treaty) is absolutely unimaginable", he said.

According to Jean-Claude Juncker, it would take "10 to 15 years" for another treaty to be established.

And a rejection of the Constitution would also lead to "external observers" not knowing what direction Europe wants to take anymore, which means that the "economy will not get better with a No", Mr Juncker pointed out.

This is why the ratification process should go on in other countries, even if France says No, the current EU president stressed.

"I would find it extraordinary to say to the other nations that they can stay home, as France has decided for everybody else", Mr Juncker said.

But according to The Times, ministers in the British government do not find it likely that the ratification would go on if both the French and the Dutch say no.

Instead, they believe President Jacques Chirac will have to either promise renegotiation or declare the constitution dead.

And although renegotiation looks doubtful, it is possible that the incoming British presidency might be able to bring into force parts of the constitution that can be enforced without a treaty, such as mechanical changes, like scrapping the six-month rotating presidency of the EU.