By Andrew Callus
PARIS (Reuters) - France's presidential election campaign, until now apparently sleepwalking towards victory for ex-Prime Minister Alain Juppe, jolts into life on Wednesday as a far younger man launches his bid for the job and polls show the 71-year-old losing his lead.
Juppe has fought his campaign so far on a centrist platform to the left of his main rival for the centre-right ticket, Nicolas Sarkozy.
Polls until this week showed Juppe winning the primaries of the Les Republicains party and its centre-right allies which begin on Sunday.
He would then be propelled in the election itself by voters of the mainstream right, centre and left, all determined to keep the popular far-right National Front party leader Marine Le Pen from power, they showed.
But two things have happened in recent days to change all that.
Since the weekend, opinion polls have been showing Francois Fillon, the prime minister under Sarkozy's first presidency between 2007 and 2012, gaining ground fast as the "third man" in the Les Republicains ticket contest.
On Tuesday night, an Opinionway poll for Atlantico showed Fillon neck-and-neck with Sarkozy in second place for the first round of the primaries behind Juppe.
As in the presidential election itself, only two candidates go through to a run-off second round, and Opinionway shows Fillon beating Juppe by 54 percent to 46 should he progress at Sarkozy's expense.
Fillon once espoused Thatcherite free market policies in determinedly dirigiste France, but broadly speaking, he sits somewhere in the policy stakes between Juppe and Sarkozy.
Other polls have also shown Fillon gaining votes as Juppe loses them. Much of Juppe's support is seen as an ephemeral 'least-worst' choice, while the abrasive Sarkozy's backers are more hard-core in his favour.
The other fly in Juppe's ointment is Emmanuel Macron, a pro-business reformist economy minister in President Francois Hollande's current Socialist government before he quit this year to set up his own political movement.
Macron's actions have suggested for months he will be a candidate. He is due to make his official announcement on Wednesday, just days ahead of Juppe's big test, according to a source close to the 38 year-old investment banker.
Although among France's most popular politicians, Macron is not an elected politician and has no party apparatus behind him, so he may struggle to turn his own campaign into a winning one.
However, he is widely seen as likely to take centrist votes from Juppe, one of whose supporters on Tuesday roundly condemned the timing of his move.
"He said, broadly - 'I am going to do politics differently, outside of political clans and parties'," said member of parliament Benoist Apparu on BFM TV.
"And then the first thing he does is a purely political, calculated, electoral move, telling himself, 'I will try and falsify ... the result of the centre-right primary'".
Macron is also likely to further fragment the already divided left-wing vote as speculation has increased this week that prime minister Manuel Valls will stand instead of - or as well as - the deeply unpopular Hollande.
An October poll published by Odoxa put Macron at the top of a list of potential presidents from the left, with 49 percent considering him a good head of state. Valls came second at 42 percent.
Adding to the uncertainty is concern in the wake of Britons' vote to quit the European Union and Republican Donald Trump's victory in U.S. presidential elections that opinion polls are failing to capture the scale of the populist vote being courted by Sarkozy and Le Pen.
(Corrects paragraph nine to read Sarkozy, not Macron.)
(Reporting by Andrew Callus; Editing by James Dalgleish)