Police say they have uncovered a plot by the Camorra, the Naples Mafia, to murder Roberto Saviano, the author behind the hit film Gomorra, by blowing up his car "before Christmas".

Mr Saviano, 29, has been under 24 hour police protection because of death threats since his exposé of the Camorra was published two years ago. Today it emerged that gangsters had vowed to kill him because the book and the film are giving worldwide audiences a devastating insight into the Camorra's brutal grip on daily life, from bars, shops and the fashion business to waste disposal.

Anti-Mafia police in Naples have opened an investigation into the plot, in which Mr Saviano and his plain clothes guards — who have become his friends and address him admiringly as "The Captain" — were to be blown up while travelling by car on the Naples-Rome motorway.

Police said that they had been tipped off about the conspiracy by a Camorra pentito, or informer, from the violent and ruthless Casalesi clan of the Camorra, which features prominently in Gomorra. The clan has been the target of a police crackdown over the past few weeks after the deaths in August of six African immigrants at the seaside town of Castel Volturno near Naples in a drugs-related turf war.

The pentito told police that Camorra bosses had said Gomorra was "creating too much noise, it has become a phenomenon''. Mr Saviano commented: "All I can do is carry on as before: resist, resist, resist."

Giuseppe Setola, the head of the Casalesi gang suspected of the Catel Volturno murders, has so far avoided arrest. He is reported to have ordered the detonator for a bomb from underworld arms dealers.

Mr Saviano was last seen in public a year ago at an anti-Camorra rally in Casal di Principe, the Naples suburb where the Casalesi clan has its stronghold. Walter Veltroni, leader of the centre-left Opposition, said it would hold a rally at Casal di Principe next month.

Mr Saviano told La Repubblica this week that: ''Life under siege has changed me for the worse, turning me into a suspicious and taciturn recluse." He added that living in hiding had ruined ''an important relationship", and said that if he could turn the clock back he was not sure he would write the book again "knowing what I know now''. He revealed that he let off steam by boxing with his guards.

The centre-right Government of Silvio Berlusconi has deployed troops as well as police to the Naples area to take on the mob in what Roberto Maroni, the Interior Minister, has called "a civil war". The film version of Gomorra, directed by Matteo Garrone, won second prize at this year's Cannes Film Festival and is Italy's contender for Best Foreign Film Oscar. The book has sold 1.2 million copies in Italy and been translated into 42 languages.

Mr Saviano said that the Camorra was alarmed because "millions of people" had not only read his book but also seen the film, which uses local people as well as actors. In an ironic twist Bernardino Terracciano, 53, a Naples man who plays himself in the film, was arrested last weekend on suspicion of extorting protection money.

Biovanni Venosa, a local man who also plays a Camorra boss in the film, was detained in July, and a third man, who plays a hitman, is under investigation for drug dealing.

Rosaria Capacchione, 43, a second anti-Mafia journalist in Naples, was also given 24-hour protection this week after thieves broke into her home and stole a plaque awarded to honour her investigative journalism. Nothing of value was taken, and the break in was interpreted as a Camorra warning.

Last week Stanislao Cantelli, the uncle of two Camorra pentiti whose evidence has led to mass arrests, was shot dead in a revenge killing near Naples while playing cards at a working men's club only yards from an army checkpoint. The killers escaped on a motorbike, sending an apparent signal to the authorities that the Camorra acts with impunity on its own territory whatever measures are taken to suppress it. Mr Maroni remarked: "I never thought a few hours would be sufficient to win a war."

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