Supporters of Segolene Royal accused opponents within France's Socialist party of fixing a bitterly contested leadership vote and demanded a re-run, plunging the leftist opposition into crisis yesterday.
Socialist officials said Martine Aubry, architect of the controversial 35-hour work week, defeated her arch rival Royal by just 0.04 percentage points, or 42 votes, in Friday's ballot of the party's 233,000 members.
The result was a gift for French President Nicolas Sarkozy, who defeated Royal in last year's presidential election and has taken advantage of the enfeebled opposition to speed ahead with his domestic reform programme.
Royal's camp refused to accept the leadership result and urged Socialist members to rise up against the party hierarchy, which had openly backed Aubry's candidacy.
"There was fraud, there was cheating, there is deep doubt about last night's result," parliamentarian Manuel Valls said.
"I call for the membership to rebel ...our supporters cannot put up with this any more. The only way out of it is to hold a second vote," he told TF1 television.
Senior leftist figures urged restraint, fearing the ballot could tear apart the Socialist party, which was refounded by former President François Mitterrand in 1971 but has been riven by deep divisions for years.
Aubry, the daughter of former European Commission President Jacques Delors, made no immediate comment on the accusations and left it to her inner circle to defend the result.
"No one can deny the situation is complicated, but no one can deny that Martine Aubry is the new first secretary of the Socialist party," said her close adviser, François Lamy.
Royal's supporters pointed the finger to results from two Socialist chapters which they said were suspicious - one of which is controlled by Aubry herself and the other by her close supporter, former prime minister Laurent Fabius.
Socialist officials said Royal's side had signed off on the results from both locations overnight but outgoing party leader, François Hollande, promised to review any complaints.
"It is my job to ask both candidates to show sang-froid," said Hollande, who is Royal's estranged partner.
Political commentators said the party might not survive the growing crisis.
"This is a disaster for the Socialist party, for democracy, for the image of politics and for the two candidates," said veteran analyst Alain Duhamel. "This is an unsustainable situation for the Socialist party," he told RTL radio.
Royal had presented herself as a force for change and promised to inject fresh blood into the party, but her critics accused her of being inconsistent and said she would drive the Socialists to the centre of the political spectrum.
Aubry had promised to anchor the party firmly to the left and drew together a disparate alliance of Socialist veterans to try to derail Royal, who has solid grassroots support.
Mayor of the northern city of Lille, Aubry is best known for penning a 2000 law which cut the work week to 35 hours from 39.