French politics will stray into uncharted territory this weekend when left-wing voters will be invited to take part in the country's first "open" presidential, primary election.
If pollsters are correct, little doubt remains about the identity of the centre-left challenger to President Nicolas Sarkozy next year. This week, the former Socialist party leader, Francois Hollande, 57, extended his lead in the opinion polls.
Tomorrow's vote will be the first time that any French political party has opened its choice of presidential candidate to all comers. Anyone who has a national voting card can cast a ballot, so long as they pay a minimum of €1 ($1.70) to the Parti Socialiste and declare themselves to share the "values of the left".
Socialist party officials hope that as many as 2 million people will take part. Since the breadth and political chemistry of the electorate is uncertain, opinion polling is more hazardous than usual. The five candidates who are trailing behind Hollande, especially the party leader, Martine Aubry, predict that the pollsters will be badly embarrassed this weekend. Some of Hollande's supporters say that he might reach 50 per cent, enough to be elected outright and pre-empt the two-candidate second round a week later.
One poll this week showed Hollande with more than 50 per cent support among Socialist party members and 46 per cent support among those left-wing sympathisers who say that they are certain to vote.
Despite the American origins of the primary idea, this will be a very French election. There has been little controversy and a series of worthy but dull television debates. The intention is to create nationwide, rather than partisan, momentum behind a centre-left challenger long before the presidential election next April and May. Since both Hollande and Aubry are predicted to defeat Sarkozy easily, the experiment can be said, so far, to have been a success.
Hollande has been the great beneficiary of the aborted ambition of the former Socialist Finance Minister, Dominique Strauss-Kahn. DSK was the overwhelming favourite to win the Socialist primary when he was arrested in New York in May on attempted rape charges, which have since been dropped.
Hollande, humorous, likeable, sharp-minded but unexciting, has also benefited from the debt crisis, the unpopularity of Sarkozy and the corruption investigations which have swirled around the President's friends. He promises to be a "normal, honest and moral" President.