The EU Commissioner for Enlargement has said that if the Irish electorate rejects the Nice Treaty, the State will have to interpret whether the result means Irish voters are against enlargement or just against other aspects of the treaty.
Mr Günther Verheugen, in an interview with the BBC World Service broadcast at the weekend, said if there was a No vote, a "green light" would be needed from Ireland for enlargement to proceed.
He said, however, that a No result would be "a very very serious obstacle" to enlargement.
"The problem is nobody can clearly forecast whether an Irish No means that the Irish electorate rejects enlargement or whether the Irish electorate rejects only some provisions of the Treaty of Nice which have nothing to do with enlargement, and I do not believe that the member-states or European institutions can make such assessments.
"My view is that in the case of a second No we would need a clear green light coming from Ireland that we can continue with enlargement," he said.
If Ireland voted No, enlargement would be off "for the moment" and "the Irish must then tell us whether we can continue with enlargement or not", he added.
He went on, however, to say that a No vote would end the Nice Treaty. In that event he said: "Nice has failed. We do not have the Treaty of Nice".
Last week the Tánaiste, Ms Harney, said the Nice Treaty was the only agreed basis on which enlargement could proceed and if rejected there was no Plan B. "It is the Irish people who have sovereign authority on this issue and it is not for the Dáil to reinterpret in any way why the people voted in any given referendum."
Asked at the weekend about reports that EU officials could try to come up with some legal formula to stop Ireland blocking the whole Treaty, Mr Verheugen said he had no idea what these provision could be.
"For the time being I can only tell you that I have not the slightest idea whether they exist," he said.
"A political precondition even for considering another solution is actually a signal from Ireland that it can go ahead with enlargement. If Ireland tells us the referendum means that the Irish electorate does not want enlargement, then it's over, finished," he added.