Ireland is ready to call a rerun of its referendum on the Lisbon treaty in the autumn if EU leaders meeting today agree to a series of guarantees stating that the controversial document will not change the country’s taxation, abortion laws or military neutrality.

The decision will come exactly a year after Irish voters stunned EU leaders by rejecting the redrawn EU constitution and follows polls suggesting that they are prepared to back the document, which creates the jobs of EU president and foreign minister.

Brian Cowen, the Taoiseach, astonished fellow leaders at their summit in Brussels last night by demanding that the guarantees he needs to win the referendum must be in the form of a legal protocol attached to a future EU treaty. The next one would probably be the accession treaty for Croatia, which hopes to join in 2011.

Britain was among several member states reluctant to give the commitment because all EU treaties have to be ratified through Parliament — giving the Conservatives an opportunity to reopen debate on the treaty itself or even to vote against the protocol.

One EU diplomat said: “It would give David Cameron a dilemma — does he support the enlargement of the EU, as he says he does, or does he block it to block the Irish protocol?”

British diplomats argued that Mr Cowen should be satisfied with having the guarantees for Ireland included in the conclusions of the leaders’ summit today, which would also give them legal force.

But Mr Cowen was still insisting that only a protocol added to a future treaty would satisfy sceptical Irish voters and help him to win the referendum.

In a private letter to Gordon Brown, seen by The Times, Mr Cowen wrote: “In order to provide the maximum possible legal reassurance to the Irish people, I need to be able to come out of our meeting and state, without fear of contradiction, that the legal guarantees . . . will in time acquire full treaty status by way of a protocol.

“I require a clear and unequivocal commitment that, at a future point after the Lisbon treaty enters into force, the legal guarantees contained in the decision will be attached to the EU treaties by way of a protocol.”

He referred to commitments made to him in December by Nicolas Sarkozy, the French President, who suggested that the Irish guarantees could be attached to the Croatian accession treaty.

Asked whether he could accept Mr Cowen’s demands, Mr Brown said that discussions were continuing. He added: “The important thing for everybody is that we want to make sure we do the right thing by Ireland and by Europe.”

Mr Cowen is expected to call the referendum for late September or early October.

• EU leaders gave their backing last night to José Manuel Barroso for a second five-year term as President of the European Commission. The former Portuguese Prime Minister was seen as the only viable candidate.

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