Freed of the burdens of state - or impelled by a desperate desire to get back into the headlines - the former Italian prime minister Silvio Berlusconi is enjoying a summer of grand and improbable spectacles.

To celebrate Italy's big summer bank holiday on 15 August (the feast of the Assumption of the Virgin Mary), he organised the secret building of an artificial volcano in the sprawling though congested grounds of his Sardinian holiday home, Villa Certosa.

There on this lonely, splendid stretch of the Costa Smeralda, already adorned with his Greek-style amphitheatre, a garden with 1,000 cacti and at least five swimming pools, the media tycoon ordered the fashioning of this fake volcanic cone on the top of a new artificial hill which has already excited the disapproving attentions of the local planning authorities.

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Mr Berlusconi is still the leader of Italy's opposition despite rumbles of rebellion from his allies and, as such, has been in regular touch with Prime Minister Romano Prodi in recent days over Italy's plans to send up to 3,000 soldiers to Lebanon with the UN force. But in between, he was putting the finishing touches to the most preposterous coup de théâtre of his extraordinary career.

"Around midnight on Ferragosto [the 15 August holiday]," reported Corriere della Sera, "the Cavalier laid on 'a crazy idea' for his 30 carefully selected guests."

On the artificial hill, an anonymous witness said, he had set up "a confection of lights, optical fibre and smoke that really made an impression, a fantastic idea, to see it at night it really seemed the cone was erupting and lava was pouring down it." The volcano effect was compounded by artificial earth tremors.

Neighbours of Berlusconi were so alarmed by the belching flames that they called the fire brigade. At the villa's front gate the firefighters were apologetically sent on their way.

If this was Mr Berlusconi's way of telling the world that he is still a force of nature, the surprise party he laid on last month for the 50th birthday of his wife, Veronica Lario, reminded Italy that he is more like an old-style Arabian sheikh than any other democratic leader one can think of.

He insisted on Ms Lario taking a mystery trip on one of his private planes without him; it landed in Marrakesh, where she was escorted to a restaurant.

During the meal she was entertained by a troupe of gnawa dancers, one of whom turned out to be her husband in disguise. He whipped off his veil, took a diamond necklace out of his pocket and let rip with "Happy birthday to you".

Staged by any other politician, two such stunts in a row would be taken for sure signs of mental instability. But Italian commentators view them as Mr Berlusconi's way of warning aspirant rivals that he is in no mood to shuffle off the stage quietly.

"He has a great desire to get stuck in again," says Corriere della Sera. "A volcano, an earthquake... Silvio Berlusconi assures his people that he is over post-election depression. 'I'm the leader of the opposition', he is saying, 'and if Prodi wants to deal with anybody he'll have to deal with me'."

n Internet experts have warned that a fake BBC "news item" claiming that Mr Berlusconi had been murdered by an Israeli soldier contains a worm that will damage computers.