From friends to enemies, to wary allies: now France's new alliance targets middle-of-the-road

In Texas, it is said, there is nothing in the middle of the road except yellow lines and dead armadillos. In France, the political middle ground is more like a giant amoeba: constantly splitting and re-forming and splitting once again.

The two most powerful centrist barons in France are announcing the creation of an alliance to fight the municipal and European elections next year and, implicitly, the presidential election in 2017.

François Bayrou and Jean-Louis Borloo - once friends, later enemies, now wary allies - will call their movement "L'Alternative". They plan to fill the vacuum between Francois Hollande's unpopular, governing Left and a main centre-right opposition party, the UMP, increasingly drawn towards the populist rhetoric of the far right.

If they succeed, the main beneficiary could, paradoxically, be Marine Le Pen's face-lifted National Front. A powerful centrist presidential challenger in 2017 could take enough votes away from the main centre-right candidate, or from President Hollande, to allow Ms Le Pen to reach the two-candidate second round.

Friends of former President Sarkozy, who has undeclared ambitions to run in 2017, have been begging Mr Borloo to abandon his negotiations on a new centrist alliance. He gave his response on Sunday evening when he sent a double tweet with Mr Bayrou to announce an inaugural press conference today.

The "Alternative" will be pro-market economically, liberal on social issues, cautiously green and enthusiastically pro-European. Its creation marks - for the time being at any rate - the death of Jacques Chirac and Nicolas Sarkozy's efforts to create a single mass party of the right and centre.

That party, the Union pour un Mouvement Populaire (UMP), was founded in 2002 from two allied but quarrelsome formations of the centre-right, the Chiraquian neo-Gaullists and a centrist federation, the UDF, created by former President Valéry Giscard d'Estaing in the early 1970s. Mr Bayrou, 62, a former education minister from the French Basque country, refused to join Mr Chirac's new movement. He ran for president in 2007 and 2012 as the leader of his own centrist party, the Mouvement Democrate (MoDem).

Mr Borloo, also 62, is a highly successful lawyer turned politician whose fiefdom is at the other extremity of France, at Valenciennes on the Belgian border. He originally joined Mr Baryou in 2002 and split with him in 2007 to join President Sarkozy's government as finance minister and then environment minister.

He toyed with the idea of a presidential run in 2012 and created his own movement after Mr Sarkozy's defeat, the Union des démocrates et Indépendants which has seven separate member parties.

Mr Borloo is said to have been distressed by the hard-right tone of Mr Sarkozy's 2012 campaign and the rightward drift of the UMP in opposition under pressure from a buoyant National Front. He and Mr Bayrou believe that an historic opportunity now exists to rebuild the French centre.

They will doubtless be reminded by the press today of some of the unpleasant remarks they have made about one another in the last six years. Mr Bayrou is said to have dismissed Mr Borloo as an "inconsistent coward. Mr Borloo accused Mr Bayroo of "killing the centre". "He doesn't work," he said. "He just has his own Cannes film festival at every presidential campaign".

A primary campaign is likely to decide which of the two will carry the centrist banner in 2017.