Sixty-five years after the fall of Mussolini, the fascists are back at the gates of Rome. Leading the charge is Gianni Alemanno, a firebrand leader of Italy's neo-fascists, whose promise to get tough with illegal immigrants is threatening to knock the left out of city hall when Rome votes in the second round of the mayoral election this weekend.

The fact there is even going to be a run-off vote is a major embarrassment to the left. Last time around, its candidate Walter Veltroni won outright, capturing nearly two-thirds of the votes. But this year, the centre-left candidate Francesco Rutelli, who ran Rome between 1993 and 2001, won just 46 per cent with Mr Alemanno on 40 per cent and forcing a second round.

Rome has been a citadel of the centre-left for the past 15 years and, under Mr Rutelli and Mr Veltroni, the city has prospered, seeing a 10 per cent rise in tourists per year, work on new subway lines, a film festival and an auditorium complex that sells more tickets than any other in the world. But while Rome's left-leaning chatteratti have few complaints, outside the city's gilded centre the problems have been piling up.

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Feeble policing and laissez-faire policies on the city's outskirts have resulted in urban degradation and the mushrooming of shanty towns of illegal immigrants. Crime levels remain low but the mugging murder of a housewife by a gypsy last year sparked a backlash against immigrants, particularly aimed at Romanians and gypsies.

As mayor at the time, Mr Veltroni tried to defuse the panic by demanding an emergency law to expel immigrants from within the EU without legal process. The law was passed by the national government, led by Romano Prodi but with so many caveats that it has not done the job intended.

Mr Alemanno has been riding a surge of support based on his promise to get tough with illegal immigrants – and in particular to expel 20,000 gypsies and other immigrants living in Rome who have broken the law. The widely reported rape last week of a student from Lesotho on the city's outskirts, for which a Romanian immigrant has been arrested, has only inflamed the campaigning.

Should Mr Alemanno win, it would be a tremendous feather in the cap of his ally, the newly elected Prime Minister Silvio Berlusconi. The billionaire businessman defeated Mr Veltroni in the general election earlier this month and seizing the Eternal City from the left would make that victory sweeter.

Yesterday, as Italy marked its day of liberation from fascism and Nazism, both Mr Alemanno and Mr Rutelli invoked the heroic struggle of the nation against the Nazi enemy.

Yet Mr Alemanno has received support in his campaign from Francesco Storace, a former neo-fascist colleague who has remained true to his hardline roots. Last week Riccardo Pacifici, the newly elected president of Rome's Jewish community, publicly appealed to Mr Alemanno not to align himself with Mr Storace's party, La Destra (The Right), "which has listed fascism among its values".

Mr Storace responded belligerently to the Jewish leader's charges. "The Jewish community must ask our pardon for the shameful campaign they have conducted against us," he retorted. "I am not anti-Semitic and this is an offence which can only be washed away by an apology."

Yesterday, Rome's Jews were taking it in their stride. "Rutelli's a thief and Alemanno's a cuckold," said one resident. "They're both as bad as each other."

Who is Gianni Alemanno?

It is the CV of a classic extremist: joined a neo-Fascist party as a youth; arrested for beating up a young leftist; arrested again for throwing a Molotov cocktail; eight months in jail on remand; acquitted on both charges; arrested for attacking police during a visit by President Bush Snr. Then abruptly in 1994 Gianni Alemanno and the rest of his party went straight, abjuring Mussolini, renouncing Fascism, and trying to rebrand the National Alliance as an ordinary European conservative party. Now Mr Alemanno is walking a tightrope: trying to persuade middle-of-the-road Romans he means no harm, while baring his xenophobic teeth to the neo-Fascist faithful. Complicating the picture is the fact he has been a practising Zen Buddhist for 15 years – and his meditation teacher is a card-carrying Communist. Which is why his calls for "inter-religious dialogue" may not be as empty as they sound.