All eyes on Ireland as voters determine future of EU treaty

As polling stations opened, all eyes were on turnout amid hopes among the No campaign that anything less than 40 per cent would kill off the Brussels blueprint.

The Irish Republic is the only nation out of the EU's 26 states to give the public a direct say on the treaty. All other countries have left the issue to their individual parliaments, but Ireland is legally obliged to hold a popular vote on any changes to its constitution.

Irish youngsters Kitty Bunnetta Ody and Robyn Neilan pose in front of a Fianna Fail Ad urging a Yes vote in the Lisbon Treaty Referendum

Europe has 300 million citizens but Ireland's three million voters, one per cent of the EU population, effectively have a veto on the plans.

Experts anticipate a turnout of no more than 50 per cent. With many voters undecided, opinion polls suggest the result will be close and the weather could prove crucial. Rain was forecast in many areas and a washout could depress turnout.

The treaty aims to streamline the union's voting system, create a new president and a foreign policy supremo.

A No vote would plunge the EU into crisis because the treaty cannot be implemented without approval from every member state.

Britain is set to approve the treaty in coming weeks as the House of Lords falls into line with the Commons' decision to back it.

Labour has been accused of betraying its 2005 manifesto pledge to hold a referendum but ministers claim that the Lisbon treaty is substantially different from the constitution.

All the main Irish political parties back the treaty but the No campaign has been putting up a strong challenge, backed by Eurosceptic business chiefs.

In 2001, Irish voters almost wrecked EU plans to expand eastwards when they rejected the Nice treaty. It was only passed in a much-criticised second vote.

Ireland's EU Minister, Dick Roche, predicted that the Yes campaign would win but the result would be "very, very close".

The No campaign is a broad coalition ranging from lobby group Libertas to Sinn Fein, the only party in parliament to oppose the treaty.

Sinn Fein leader Gerry Adams said a successful No vote would give Ireland's "government a strong mandate to negotiate a better deal for Ireland".

Ireland's Prime Minister Brian Cowen has accused opponents of the treaty of "sheer inaccuracy and absurdity" and said Ireland could not get a better deal than the one on offer.