Juppé fails to end UMP leadership dispute France's centre-right opposition was thrown into renewed deadlock on Sunday night when Alain Juppé, the former prime minister, said his efforts to negotiate a solution to the party's furious leadership dispute had failed. After a meeting lasting less than an hour with François Fillon, former premier, and Jean-François Copé, former budget minister, Mr Juppé said conditions for his mediation between the two feuding candidates to head the UMP party had not been met. "My mission is over,"" he said. The collapse of the talks left the UMP locked in an impasse over who will succeed former president Nicolas Sarkozy as the party's leader against François Hollande, the socialist leader who defeated Mr Sarkozy in May's presidential election. Mr Juppé, a co-founder of the party, has warned that the UMP is in danger of splitting over the bitter battle for the presidency of the movement. Mr Fillon said he would now take legal action, which Mr Juppé has described as a "nuclear weapon." The dispute is the most serious crisis to have hit the UMP since it was founded a decade ago to unite the disparate factions - from Guallists through liberals to the hard right - that make up France's mainstream right. Party supporters fear the Fillon-Copé battle will play straight into the hands of the far-right National Front of Marine Le Pen. Mr Juppé"s intervention failed despite a clear message from Mr Sarkozy made public via the French news agency AFP on Sunday that the former president was backing his effort to bring the two warring candidates together. The party has been locked in a vicious impasse since last Sunday when Mr Copé and Mr Fillon both claimed victory in a leadership election that ended in a virtual tie. Mr Copé was officially declared the winner by 98 votes by the party's electoral commission on Monday, but Mr Fillon refused to accept the outcome when it emerged that some votes from France's overseas territories had not been counted. The commission admitted as much and said the missed votes would have given Mr Fillon victory by 26 votes. Both sides have exchanged angry accusations of vote rigging, with Mr Fillon accusing the party under Mr Copé"s administration - the latter has been the UMP's senior administrator for the past two years - of becoming a "mafia." Mr Copé"s team has said Mr Fillon's supporters were guilty of "massive ballot box stuffing." Mr Fillon said late last week he was no longer claiming victory and said he would comply with whatever Mr Juppé recommended as a way out of the crisis. Many neutral figures in the UMP wanted Mr Juppé to assume temporary control of the party and prepare for new elections next year. But Mr Copé, suspecting Mr Juppé of siding with Mr Fillon, has refused to yield, putting his faith instead in the party's electoral review process, which is under way. But Mr Fillon's camp has said it is run by a pro-Copé clique and has refused to co-operate with the review panel.