After a six-week surge by Mr Bayrou, 55, a farmer and former Education Minister, the CSA polling firm yesterday gave him 24 per cent of first-round voting intentions.

Ms Royal was at 25 per cent and Mr Sarkozy at 26. The BVA firm put them at 21, 24 and 28 per cent respectively.

“Anything can happen. It’s totally open this time,” said Jean-Daniel Lévy, of CSA. “It is quite clear that, since this morning, all the [campaign] meters have been reset at zero.” The sense of uncertainty is reflected by polls showing that more than 40 per cent of voters have not made up their minds.

One uncertainty was removed yesterday when President Chirac signalled that on Sunday he will announce his retirement from politics after 40 years. No one imagined that he would seek a third term, but he has unsettled Mr Sarkozy, 52, the heir to his party, by keeping open the option. Mr Chirac, 74, is not expected to endorse Mr Sarkozy, with whom he has been in dispute for a decade.

With his anti-establishment rhetoric and amiable demean-our, Mr Bayrou is winning conservative converts who are reluctant to vote for the tough-talking Mr Sarkozy. But the immediate threat is to Ms Royal, 53. The Socialists’ chief polling expert has said that “there is now a real statistical risk for Ségolène in the first round,” le Monde reported. Mr Sarkozy would face a grave threat if Mr Bayrou eliminated Ms Royal and reached the second round on May 6 with the Left and Centre lining up behind him.

The BVA agency found that at present Mr Bayrou would defeat Mr Sarkozy by 55 to 45 per cent. But Mr Sarkozy would win by 53 per cent to 47 if his opponent were Ms Royal. Taking account of this, Mr Sarkozy’s team is pulling its punches from Ms Royal, hoping that she will survive into the second round. He is trying to woo the Centre while maintaining his appeal to hard-Right voters tempted by Jean-Marie Le Pen, the leader of the National Front.

In a move to counter Mr Bayrou, Mr Sarkozy has recruited as his campaign president Simone Veil, 79, a former centrist Cabinet minister who enjoys almost saint-like status as a pioneering woman politician. A survivor of Auschwitz, Ms Veil legalised abortion in 1975 as Health Minister under President Valéry Giscard d’Estaing, the founder of Mr Bayrou’s UDF.

Sego and Sarko have united to attack the interloper in their duel. Mr Sarkozy’s spokes-woman dimissed Mr Bayrou as “a bearer of right-wing values, but with much less ambition, unclear and less courageous” than Mr Sarkozy. The Socialists are begging supporters not to desert Ms Royal in favour of the new darling of the opinion polls. Mr Bayrou is a conservative posing as neutral, they say.

“We are saying to our electors that they must not misplace their votes,” Jack Lang, Ms Royal’s spokesman, said. “They must rally around the only candidate of change, Ségolãne Royal.” In Lyons, Ms Royal noted that at least a third of voters had not made up their minds. “I am certain that I will prove in the end that I am the candidate who will bring about change,” she said.

Mr Bayrou predicted that he would become the target of Left and Right. “They have alternated power between them for 25 years so they are going to defend their monopoly tooth and nail,” he said. “What they underestimate is that the French have decided to change.”

Mr Bayrou, who was visiting Brussels to promote his pro-European creed, said that, as “someone who has his feet on the earth”, he was not surprised by his rise. Such allusions are part of his image as a no-non-sense horse-breeder from the Pyrenees who began as a provincial teacher. To mark the contrast with the Parisian backgrounds of Mr Sarkozy and Ms Royal, Mr Bayrou has adopted as his symbol a tractor.

His project for mild reform and governing with a coalition of like-minded politicians has charmed voters weary of the war between Left and Right. Both big camps dismiss his ideas as vague, disingenuous and unworkable.

His presidential victory would raise the prospect of paralysis after parliamentary elections scheduled for June, they say. Since he leads a tiny party, Mr Bayrou would probably have to govern in alliance with either the Socialists or the UMP.

Life will now become much harder for Mr Bayrou as he loses his outsider’s aura and comes under serious scrutiny as a candidate. Le Monde and Liberation both accused him this week of dishonesty in casting himself as open to the Left because he had served only in centre-right governments.

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