Britain's leader-in-waiting joins EU treaty talks

LONDON, June 19 (Reuters) Britain's next leader Gordon Brown joined outgoing premier Tony Blair for talks with French President Nicolas Sarkozy today in a sign of Brown's close involvement in negotiations on a new European Union treaty.

During a 30-minute telephone conference, the leaders on both sides set out issues that would be deal breakers for them in negotiations among EU leaders in Brussels on Thursday and Friday, according to British and French officials.

Blair and Brown, who will take over as prime minister when Blair steps down on June 27, made it clear Britain could accept no loss of control over key areas such as foreign policy, policing, taxation or social policy, a spokesman for Blair said.

Blair has said he wants an ''amending'' treaty, much less far-reaching than the proposed EU constitution rejected by French and Dutch voters in 2005.

The new French president has been pushing for a ''simplified treaty'', which countries could ratify without consulting voters, to streamline decision-making in the EU.

''The three (leaders) agreed that the UK and France should work closely together to help create an amending treaty and that a return to a constitutional treaty as rejected by France and Holland would not be possible,'' Blair's spokesman said.

French presidential spokesman David Martinon said the three leaders had reviewed their ''red lines''. ''They tried together to find points of convergence and exit points,'' he said.

Sarkozy told the British pair what the French demands were ''so that the treaty is not left with nothing in it'', he said.

Sarkozy said earlier this month he and Blair had agreed how to reform the EU's institutions, but Spain's Foreign Minister Miguel Angel Moratinos said this week Spain and France agreed on some issues that run counter to British demands.

The outcome of the summit is crucial to Brown, who -- although he is not expected to attend the summit -- would have to ''sell'' any deal to a sceptical press and public.

Poland has threatened to block progress on the treaty unless voting rules are changed. Britain has also taken a robust stance.

British Foreign Secretary Margaret Beckett today refused to rule out a British referendum on the treaty, saying the government would first have to see what was in it. But she also said that a treaty which would win British agreement was below the threshold that would trigger a vote.

REUTERS KN SBA BST0335