France’s Socialist party has scored its first victory of the 2012 presidential election campaign. In a country where abstention has been on the rise, it is no small achievement to have convinced 2.5m people to come out on Sunday to cast a ballot in the first round of the party’s presidential primary.

The unexpectedly high turnout points to a popular groundswell in favour of a credible alternative to the centre-right President Nicolas Sarkozy. But by failing to choose decisively between the two leading moderate candidates, and allocating the role of kingmaker to a third on the anti-globalisation left, the poll has also revealed a crisis of identity that weakens the party’s chances in next year’s presidential election.

The stunning 17 per cent result from Arnaud Montebourg, the outsider who wants banks under government instruction, shows the still powerful hold over the French left of inward-looking, protectionist ideas. Resolving these tensions while keeping the party unified will be the main challenge for next Sunday’s final-round winner.