Brussels  - Ireland cannot accept anything less than a full treaty to convince its people that the European Union's Lisbon Treaty will not change their neutrality and family laws, the country's prime minister wrote ahead of an EU summit on Thursday.

"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," Brian Cowen wrote to British Prime Minister Gordon Brown.

"This is necessary if I am to call, and win, a second referendum" on the Lisbon treaty, which Irish voters rejected at a referendum in June 2008, Cowen wrote.

The treaty is meant to make the EU more efficient, but it cannot come into force until every member state has ratified it.

Post-mortem analyses showed that Irish voters rejected the document out of fears that the treaty would end Ireland's neutrality and take away its control of tax law, family law and labour and social guarantees.

At a summit in December, EU leaders promised to give Ireland "legal guarantees" that the treaty would not affect those issues.

But controversy remains over the question of how the guarantees should be passed into law.

Ireland wants EU leaders to back the document as a legally-binding "decision of the EU", and then to ratify it as a protocol to the EU's founding treaties, giving it fundamental legal weight. Irish officials suggest that the ratification could be done in tandem with another EU treaty, such as a possible accession treaty for Croatia.

But other EU member states say that they do not want to have to ratify the document, since this could re-open debate on the deeply unpopular Lisbon treaty among their own citizens.

"It would be quite strange to vote on the ratification of Croatian accession, and then suddenly find out there are some kind of pages on the guarantees for Ireland," Lithuanian Prime Minister Andrius Kubilius said as he arrived in Brussels for the summit. (dpa)