Several million Italians were today voting to elect the man whose unenviable job will be to try to unseat Silvio Berlusconi.

True to its name, the Democratic party (PD), Italy's biggest opposition group, chooses its leader by popular ballot. Anyone of 16 or more who is legally resident in Italy can pay €2 to take part. The election was held against a background of scandal. Piero Marrazzo, the PD governor of Lazio, the region around Rome, resigned on yesterday after it emerged that Carabinieri officers had been planning to blackmail him with a video reportedly showing the married governor with a transsexual.

It was the latest blow to a party that lags Berlusconi's in the polls, despite a string of sex scandals involving the prime minister. In February, the PD's former secretary, Walter Veltroni, stepped down after a heavy defeat in a regional poll.

Dario Franceschini, a former Christian Democrat who was chosen as stopgap leader, is one of the two main contenders for the succession. But the favourite is Pierluigi Bersani, a tough ex-communist and former minister in the centre-left government which lost office last year.

Bersani emerged from a ballot of party members with more than half the vote. Franceschini was hoping that vigorous attacks on Berlusconi would enable him to outflank his rival in the popular vote.

Not for the first time, Italy's prime minister succeeded in wrapping himself in an air of mystery at the weekend. His return from a "private" visit to his friend, the Russian prime minister Vladimir Putin, was delayed until yesterday, officially because of a snow storm. However, weather conditions in St Petersburg were reported normal for the time of year.