The Cavalier is back on his horse. After days of confusion and self-contradiction, on Friday Silvio Berlusconi was his rambunctious old self again, confirming that he will indeed fight Italy's coming general election. He claimed – on the basis of privately commissioned opinion polls with which he is said to be updated daily – that his stunning decision one week ago to lead his party, the People of Liberty (PdL), into the next elections has already boosted its chances.

"My return has already produced a positive effect," he told one of his own TV channels. He called it "the B effect". "If I were to lead the party," he bragged, "we could recover all the votes we obtained in 2008, the votes of all the disillusioned voters who are still out there and who have not gone over to any other party. We will appeal to them, and we are convinced they will never allow the left to win."

With a new wench on his arm – 27-year-old Francesca Pascale, a former shop assistant from Naples who gained his attention after launching a "Silvio, we miss you!" fan club – the media mogul was doing his best to convince himself and the millions who have repeatedly voted him into office that nothing had changed since the days of his glory.

But it's not only the much repaired and heavily pancaked face that has aged cruelly since he was forced to resign 18 months short of his full term. With a corruption scandal forcing the resignation of his truculent old comrade Umberto Bossi, the founder and leader of the separatist Northern League, and with the PdL riven by corruption allegations and dissent, today Mr Berlusconi can command less than 20 per cent of the Italian electorate, compared with the 30 per cent loyal to the coalition of the centre-left Democratic Party and the post-communist Left, Ecology, Liberty (SEL) party.

The somersaults Mr Berlusconi has performed in the past week give away how weak he has become. He has sniped at Mario Monti, the economist technocrat who took over as prime minister 13 months ago, ever since the latter came to power, and it was his party's decision last week to withdraw parliamentary support that prompted Mr Monti to announce his resignation. But this week, in one of the bizarre U-turns for which he is famous, Mr Berlusconi offered to support Mr Monti if he accepted the leadership of the centre-right. If he turned him down, then he, Mr Berlusconi, would be the party's candidate. Mr Monti responded with commendable restraint: "First they take away their support, then they propose me as their candidate. Thanks, but let's have a little coherence."

While few in Italy outside the circle of Berlusconi loyalists see the former PM as having a prayer of getting back into power, his re-emergence – "the Return of the Mummy" was how the French daily Libération styled last week's coup de théâtre – has undoubtedly rendered election predictions even more hazardous than usual. "These are the most unpredictable elections in years," said John Foot, professor of Italian history at University College London. "It's not worth trying to predict anything. You will just be proved wrong straight away."

Another new factor is bedevilling efforts to read the Italian runes: an acerbic, grey-bearded comedian called Beppe Grillo. An accountant by training, Mr Grillo, 64, became a comedian by accident and was one of the most bankable stand-ups on Italian television in the 1980s. But his political intelligence and knowledge of the world of money frequently erupted through the gags, and in a country where satire is a risky vocation he found himself banned from the airwaves after teasing the Socialist Party under its then leader Bettino Craxi about corruption.

Turning his back on TV, he built a huge new audience through live shows in which anti-establishment political content steadily elbowed aside the comedy. His obsessions were legion: polluting rubbish incinerators, freedom of speech, non-renewable terms for MPs, expansion of public transport and green areas of cities. He gained a huge following after publishing the names of all MPs convicted of corruption in full-page adverts in the national press, and demanding that they be barred from parliament.

Gradually be became a political figure in his own right, lecturing the European Parliament in 2007 on the problem of corruption in Italian politics. Finally, in 2009, his populist political bandwagon mutated into a party, called Movimento 5 Stelle (Five Star Movement), which to the astonishment of many is now the second most popular in the country, after the centre-left Democrats. In the two real tests it has faced since 2010 it has gained up to 20 per cent of the vote.

Mr Grillo's success is a measure of the volatility of Italian politics and of popular disillusionment with conventional politicians. Yet there is no shortage of commentators warning that he is a false prophet, representing exactly the sort of charismatic megalomania for which Italy seems to have an incurable weakness.

There is no love lost between Italy's two political comedians, Mr Grillo and Mr Berlusconi. One might think that the former's nickname for the former prime minister, lo psiconano, "the psychotic dwarf", would be enough in itself to prevent any kind of alliance between them.