Mr Pahor was in Italy for a working visit to discuss greater economic co-operation between Rome and Ljubljana, talks on companies from the neighbouring entering foreign markets jointly, and the drafting of budgets in the current economic crisis.

"Europe cannot truly take decisions because decisions must be taken unanimously and that cannot continue," said Mr Berlusconi.

The concept of a ‘core Europe' moving ahead toward further integration rears its head regularly when movement forward on a particular policy is blocked by a minority of member states.

Various politicians and academics have advocated the idea that an inner core of EU member states drive forward with deeper integration via the development of a new organisation, often described as a European Federation, alongside the existing European Union.

Some experts believe that even if the Irish approve the treaty, such a move remains inevitable as the union expands beyond 27 member states.

When the shoe was on the other foot however, and Italy appeared to be left outside a core of EU countries, Rome argued strongly against the idea.

In January 2004, when the leaders of France, Germany and the UK met in Berlin to adopt a common approach ahead of a spring EU summit and patch up differences that had emerged over the Iraq war, Italy, then the fourth largest economy in the Union, was left out.

Franco Frattini, the country's foreign minister at the time, later an EU commissioner and now Italy's foreign policy chief once again, said he was opposed to a core group of countries making decisions without respect to the wishes of other states.

"There cannot be a ‘directoire', there cannot be a divisive nucleus which would run the risk of posing a threat to European integration," he said.

The comment was made also in reaction to affirmation of French support for a "pioneer group" of states made by then-president Jacques Chirac after the previous summit.

"It would be a motor which would set an example," he said. "It will allow Europe to go faster, better."

His German counterpart, Gerhard Shroeder, warned against failure to ratify the European Constitutional Treaty, the document which later was re-edited to become the Lisbon Treaty in the wake of its rejection by French and Dutch voters in 2005.

Defeat for the constitution would produce a "two-speed Europe," he said.

The UK's foreign secretary in this period, Jack Straw, backed the idea that the UK should be part of this core: "It would be logical to couple Britain with the Franco-German engine, since Europe is going to expand from 15 to 25 member states."

McCreevy, Barroso warn against No vote

Separately this weekend, Irish EU commissioner Charlie McCreevy warned that if Ireland rejected the Lisbon Treaty again, the country's economy would be hit by international markets.

"[A No vote would turn] a very very serious economic problem for Dublin into a full blown economic crisis," he said during a business lunch in Dublin, the Financial Times reports.

"International investors would take fright" he added, "at a time when our government, our banks, and our businesses need to raise more international capital than ever."

Such a vote would give a "negative signal to international money and bond markets, making it harder and dearer for the government to raise capital, to fund our exchequer deficit and for our banks to fund credit for businesses that create jobs and growth".

Also on the weekend, European Commission President Jose Manuel Barroso was in Ireland campaigning for the treaty where he warned that the No side was lying about what is contained in the treaty.

"I have seen some pamphlets that are completely dishonest intellectually and politically. They are saying sometimes lies – pure lies. They are trying to play with fear. I don't like fear, I like facts," he said, according to the Irish Times.

"It's legitimate to have different opinions – no one is forced to have the same opinion – but please, don't distort the facts. Saying, for instance, that there is a kind of minimum wage in Europe is completely false, absolutely false. It's in no treaty, no regulation. It is completely false."

Support for the Yes side is currently at 53 percent of voters, according to a poll by Millward Brown Lansdowne. The same survey put the No side on 26 percent and the undecided at 21.

The last poll published, by the Sunday Business Post on 13 September, put the Yes side on 63 percent.