Asked repeatedly by reporters whether the transfer of powers to Brussels contained in the deal would provoke a referendum in Ireland, the country's prime minister, Enda Kenny, refused to comment, saying only that the question first required a consultation with the attorney-general.

However, Irish Europe minister Lucinda Creighton this morning told Reuters that it was a toss-up whether a vote would be necessary.

"I would say it's 50-50 and we will be looking at the detail over the next couple of weeks," she said.

Elsewhere in the eurozone, Dutch Prime minister Mark Rutte insisted to reporters that a referendum in the Netherlands - where a referendum on the European Constitution in 2005 delivered a surprise No vote - would not be needed, as it concerns "no big new deals" but only "the cap-stone in the construction of the euro."

However, other parties in parliament upon which Rutte's liberals depend, have other ideas.

Rutte's minority government normally relies on the parliamentary support of the hard-right and eurosceptic Party for Freedom (PVV), with the exception of issues related to the EU. For EU-related legislation, the government requires the support of the opposition Labour Party.

Until now, the social democrats have agreed to back the government through the crisis, but have in recent days suggested that this tacit support could come to an end. 

Earlier this week, the Labour Party said that new elections were in order if any result of the EU summit amounted to a transfer of power to Brussels.

The PVV, the left-wing Socialist Party and the Greens have called for a referendum. If Labour decides that there has indeed been such a shift in powers and backs the call for a plebiscite, there would be a pro-referendum majority in the chamber.

Austrian officials have also indicated that the creation of a fiscal union would require a referendum.

Outside the eurozone, Romanian President Traian Basescu told reporters in Brussels that the treaty would need a supermajority in the parliament and approval in a popular plebiscite.

"I will meet with parliamentary groups next week and inform them about what lies ahead. In order to anchor the debt brake into our constitution, we need a two-thirds majority in the parliament and a referendum," he said.

However, the leader is committed to pushing through the deal domestically.

"For us it's politically important to join this treaty. There was already a club of 17 [eurozone member] forming and I came out against that a few times."

Meanwhile, Denmark’s new social democratic prime minister, Helle Thorning-Schmidt, did not want to speculate about Danish constitutional problems related to participation in the new treaty, but leaders of the other two parties in her governing coalition were quick to say that a referendum might be needed.

Crucially, the governing pro-EU Social Democrats depend on the support of the Red-Green Alliance, a left-wing party that saw the biggest increase in support of any party in the recent elections and a fervent critic of what it argues are the Union’s ‘neo-liberal policies’.

"In reality [the new treaty] will subsume Denmark's economic policy under decisions taken by the EU. It will be done completely on a par with what applies to the euro countries," according to Per Clausen, the parliamentary group leader.

"It must of course mean that the Danish government is preparing a referendum on the euro reservation," he said.

The Latvian government for its part has signed up to the treaty deal, but it only takes 50 members of the 100-seat parliament to demand a referendum on any major alteration of treaties.

The Baltic nation, which has introduced strict austerity measures demanded by the bloc, has seen a loss of 10 percent of its population as emigrants flee the troubled economy. Politicians, which are currently lobbying the EU institutions over the loss of European structural funds, say they feel a sense of betrayal by Europe and may threaten such a plebiscite in a gambit to win back EU aid resources.

Elsewhere, the Czech Republic does not need a referendum for the changes, but the state is home to the bloc's most eurosceptic president, Vaclav Klaus.

He does not have the power to strike down legislation endorsed by parliament, but there is no firm schedule for his signature and he has the power to drag out the procedure considerably longer than markets may be comfortable with. In 2009, the leader refused to sign the Lisbon Treaty for months.

Meanwhile, although Finnish Prime Minister Jyrki Katainen said that a treaty change is "not a problem for Finland," the constitutional committee of the parliament has found that a replacement of unanimity by majority voting in the governance of the EU's bail-out funds could result in Helsinki being forced to pay out significant sums without the chamber having any say.

As a result, the committee ruled that such a shift would be unconstitutional. A Finnish official told EUobserver that it would be "impossible" for the government to negotiate this problem away.

Correction: This article was corrected on 11 December to say that Traian Basescu is the President of Romania, not its Prime Minister.