Ireland's prime minister warned today that this week's plebiscite on the European Union's reform treaty, the second in as many years, would be final and European integration would be at risk if they rejected it again.

Brian Cowen needs to get the Irish electorate to pass the Lisbon Treaty to avert a crisis in the 27-member bloc, as well as boosting his efforts to pull the former "Celtic Tiger" economy out of one of the Western world's worst recessions.

A No vote could spell the end of his premiership and jeopardise his centre-left coalition ahead of a vote on a "bad bank" plan to resuscitate the financial system.

"Well there won't be a Lisbon 3 that's for sure," Cowen said at a final campaign news conference ahead of 24-hour broadcast ban, beginning on Thursday, on coverage of Friday's referendum.

"What is clear is that we would face into a period of extraordinary uncertainty and we could well see the development of a two-speed Europe."

Some No campaigners have argued that Ireland would be able to wring more concessions out of Brussels if they reject the treaty, intended to speed-up decision-making in the bloc, for a second time.

Cowen has already won guarantees that Ireland will be able to keep a commissioner, as well as pledges that the treaty does not affect the country's neutrality, taxation policy and strict abortion laws, to make it more palatable to voters.

Brussels needs Ireland to ratify the treaty to help pave the way for its introduction across the bloc and give it a more influential voice on the world stage.

Opinion polls suggest Ireland, with a population of less than 1 percent of the bloc's half a billion people, will ratify the treaty but there are fears anti-government sentiment could make the result tight.

A second rejection could delay European integration, weaken the euro currency and reduce the bloc's global clout. It would send Ireland's debt yields soaring and hammer its international reputation.

Diplomats have said some EU countries could try to push ahead with closer integration without other member states and form a "core" Europe.

Irish voters will go to the polls on Friday but manual counting of the ballot papers will not commence until Saturday morning and there should be early indications of the result a few hours later.