Italy's anti-politician on the verge of election sensation

The nightmare prospect that Silvio Berlusconi might return to power yet again has receded in recent weeks. He is still hugely popular, and his Freedom People party was in second place when the last opinion polls were published before the ban on polling came into effect a fortnight ago.

But his comeback has been put in the shade by the mercurial ascent of an equally magnetic and controversial figure: Beppe Grillo, a charismatic 64-year-old comedian from Genoa whose anti-political non-party, the Five-Star Movement, has come roaring from behind in recent weeks and may have taken over the number two slot, with one in five Italians said to be planning to vote for his mostly young, untried and unknown candidates. The likely presence in the next parliament of 100 or more "Grillini" puts a large question mark over the stability of any possible alliance.

With Pope Benedict XVI about to retire, President Giorgio Napolitano weeks away from the end of his seven-year term and the Prime Minister, Mario Monti, a lame-duck caretaker, Italy is entering a phase of dramatic uncertainty.

Into that vacuum has rushed the ranting, foul-mouthed, tousle-haired figure of Mr Grillo, an accountant before he became a cult comedian, whose final rally of his so-called "Tsunami Tour" of the country on Friday filled Rome's Piazza San Giovanni is said to have attracted 800,000 supporters.

Mr Grillo's simple and hugely popular argument is that Italian politics of both left and right is rotten to the core and the nation's only hope is to sack all professional politicians – "tutti a casa!" roared the Rome crowd, "send them all home!" – and replace them with honest, well-intentioned Italians who will resist the temptations of power and set their country on the road back to sanity.

"From every point of view, political, economic, social, the [politicians] are failures," he roared to the crowd in Rome. "And now something starts. We will no longer have to see ordinary people suffering and those on TV with their dickhead faces. They must all go home!"

But behind the simple rhetoric lies a sophisticated campaign in which Mr Grillo turned his back on all conventional media, refusing to be interviewed on TV or in newspapers, building a huge support base on the net with his popular blog. Masterminded by the movement's co-founder, Gianroberto Casaleggio, the approach is as original as Mr Berlusconi's was 20 years ago.

"It is extraordinary the sort of unlikely people who say they will vote for Grillo," commented James Walston, of the American University of Rome. "The majority are younger disillusioned left-wing voters but there are a good number of older ex-Berlusconi people. Once again Italy has invented a new form of politics."

Until Mr Grillo burst upon the scene, the post-election scenario that many outside Italy were praying for was that Pier Luigi Bersani's centre-left coalition would win a majority in the lower house, while the centrists clustered around Mr Monti might take the upper, which is decided region by region. Talk of a coalition has been discouraged during the campaign, but it was believed they could forge an alliance strong enough to weather the immediate economic storms facing the country.

Mr Bersani, a former Communist, is the latest lacklustre figure trying to wave the left's old banner without frightening the horses. But Mr Monti, whose translation from grim-faced technocrat to beaming candidate has lost him fans – many say he is now "just another politician" – is said to have been losing support drastically, so that all the plotting may turn out to have been in vain.

It is the essence of Mr Grillo's appeal that he refuses to discuss cutting deals with anybody: for his supporters, that's the bad old days. Instead he scatters ripe insults over rival leaders like confetti: Mr Berlusconi is the "psycho dwarf", Nichi Vendola, leader of Left, Liberty and Ecology, is "a hole without a doughnut", Mr Monti is "Rigor Montis".

It's knockabout stuff that has delighted crowds the length of the country. How it will translate into the gritty work of governance is anybody's guess.