MAJOR differences between Taoiseach Brian Cowen and British Prime Minister Gordon Brown were last night threatening to derail EU talks aimed at giving Ireland the strongest possible guarantees on the Lisbon Treaty.

Mr Cowen wrote to Mr Brown pleading with him not to block Ireland's request for such guarantees.

However, the EU leaders' debate on the issue was dramatically postponed last night, indicating a serious impasse has now developed between the two leaders.

Details of the standoff emerged as Mr Cowen warned EU leaders he could lose a second referendum on the treaty, unless promised legal guarantees on taxation, abortion laws and military neutrality were cast iron.

In his letter, Mr Cowen demanded that the guarantees he needed to win the referendum must be in the form of a legal protocol attached to a future EU treaty.

The letter was sent to all 26 other EU leaders, but it was clearly aimed at Mr Brown, who is reluctant to give the commitment because he could be forced to bring the treaty back to the House of Commons for ratification -- leaving himself open to attack by the Conservatives.

In his letter the Taoiseach wrote: "The sole purpose of this protocol will be to give treaty force to the clarifications contained in the decision, which are entirely in conformity with the treaties. I want to emphasise, sincerely, that this is necessary if I am to call, and win, a second referendum."

Mr Cowen's secret letter was sent "in strictest confidence" on the eve of the summit, but was leaked by the British yesterday.

The letter shows clearly Mr Cowen is nervous that Mr Brown's objections to the guarantees will derail the process.

"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 contained in the decision will, in time, acquire full treaty status by way of a protocol," he wrote.

Protocol

After repeatedly declining to say he was actually seeking the legal guarantees in the form of a protocol, Mr Cowen uses the word no fewer than seven times in the letter.

Foreign Affairs Minister Micheal Martin said Mr Cowen's letter "speaks for itself" in terms of setting out Ireland's position.

He stressed the Government would get the guarantees, regardless of their format.

"We will come out of this summit with legally binding guarantees," he said. "But, in addition to that, we are seeking to have them incorporated into the treaties which are being created."

He admitted the protocol status, attaching the guarantees to a treaty, would give them "full legal force".

"The purpose of the letter was to give absolute clarity. The Taoiseach was anxious there would be no ambiguity in relation to the Irish position," he said.

Mr Cowen held a one-to-one meeting with Mr Brown and contacts were ongoing last night.

Officials were worried the British objection to new EU financial regulations was the real cause of the impasse on the guarantees.

"Our concern is we are a little bit of a pawn. At the very minimum, we have the guarantees and probably will have the protocol later. But if that's all you've got, there is a flank exposed to the 'No' side," a source said.

Mr Brown said the impact of the treaty on Britain must not be affected "in any way" by the demands for the guarantees.

Britain wanted to "do the right thing by Ireland and by Europe", Mr Brown said.

"I want to ensure that the Lisbon Treaty as it affected Britain will not be changed in any way," he said.

Last night, Mr Cowen said he was "working constructively on the issues with colleagues and further discussions on the issues are continuing later".

In his letter, Mr Cowen said he recognised it would not be possible to adopt this protocol before the treaty entered into force, as many Member States have made clear that they don't want to reopen the treaty ratification process.

"However, what I do require is 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."

- Fionnan Sheahan Political Editor in Brussels