The latest poll in Ireland has revealed a shock swing to the "no" side ahead of next week's vote on the EU's Lisbon treaty.

Carried out for the Irish Times, the TNS/mrbi poll shows that those saying they intend to vote "no" has almost doubled to 35 percent (up 17 points) since their last survey three weeks ago.

The "yes" side has seen a drop of five points to 30 percent, while those undecided clock in at 28 percent (down 12 points) and seven percent do not intend to vote.

According to a detailed break down by the Irish Times of the 1,000-strong survey, the reason most often cited for voting "no" - 30 percent - is that voters say they do not know what is in the treaty or they do not understand the treaty. Only five percent cited domestic reasons for voting "no."

Those planning to vote "yes" said they would do so to keep Ireland closely involved in the EU. "Yes" supporters also said they wanted to enable the bloc to work more effectively.

The poll revealed a clear socio-economic divide, with a majority of better-off voters intending to vote "yes," and a majority among the working class planning a "no" vote. Meanwhile, older voters tended to be more positive towards the treaty, but there was only a majority of "yes" supporters among the over-50s.

The survey's result comes despite the fact that Ireland's main political parties all support the treaty, and shows there will have to be a large swing before the 12 June vote if it is to result in a "yes."

Ireland is the only one of the 27 member states to hold a referendum on the EU treaty and is facing enormous pressure to secure a "yes" vote, with a rejection likely to scupper the ratification process in the rest of the bloc.

But Dublin has had a hard time trying to sell the treaty, as it has struggled to find a headline reason for voting for the charter that the ordinary voter perceives as directly affecting them.

Reading the treaty

In addition, senior politicians, including prime minister Brian Cowen, have admitted to not reading the entire document, while deputy prime minister Mary Coughlan when questioned gave an inaccurate answer on the future number of EU commissioners foreseen under the treaty.

On top of this, a government book explaining the treaty differs in important ways to a summary of the pact produced by the referendum commission, an independent body that manages referendums in Ireland.

Instead of focussing on the detail, the government has relied on appealing to Irish citizens' generally pro-European stance, with warnings about "disasters" if the country votes "no."

The "no" side has concentrated on single issues, saying the treaty will mean Ireland loses it powers over taxes and abortion while its traditional neutrality will be undermined – all of which the government has categorically denied.

Most of Europe will be focussed on Ireland when voters go to the polls next Thursday. Some, however, are already planning for a possible "no" vote.

According to reports, the Czech Republic, which takes over the EU presidency on 1 January as the EU treaty is supposed to come into force, has prepared two papers how the EU should work in the first half of 2009 - one with the EU treaty in place and one without.