An Italian comedienne who said that Pope Benedict XVI would go to Hell and be tormented by homosexual demons is facing a prison term of up to five years.

Addressing a Rome rally in July, Sabrina Guzzanti warmed up with a few gags about Silvio Berlusconi — her favourite target for her biting impressions — before moving on to some unrepeatable jokes about Mara Carfagna, the Equal Opportunities Minister and one-time topless model.

But then she got religion, and after warning everyone that within 20 years Italian teachers would be vetted and chosen by the Vatican, she got to the punchline: "But then, within 20 years the Pope will be where he ought to be — in Hell, tormented by great big poofter devils, and very active ones, not passive ones."

The joke may have gone done well with her crowd on the Piazza Navona in Rome, but not with Italian prosecutors. She is facing prosecution for "offending the honour of the sacred and inviolable person" of Benedict XVI.

The Christian world may have been dismayed, even outraged, at the Muslim reaction in 2005 to Danish cartoons satirising the Prophet Muhammed, but Italian law enforcement appears to have had its own sense of humour failure. Giovanni Ferrara, the Rome prosecutor, is invoking the 1929 Lateran Treaty between Italy and the Vatican, which stipulates that an insult to the Pope carries the same penalty as an insult to the Italian President. Prosecution requires authorisation from the Ministry of Justice, for which Mr Ferrara has applied.

The incident has strong political overtones as Mr Berlusconi has been at pains to court the Vatican — and the Catholic vote — since returning to power for the third time in May. Last weekend he accompanied Benedict to Cagliari in Sardinia and attended mass there.

The July rally was called to protest against alleged interference by the Vatican and the Catholic Church in Italian affairs, from abortion to gay rights, but also to attack the Prime Minister for passing "ad personam" laws to protect his own interests and avoid prosecution on corruption allegations.

Mr Berlusconi, who owns Italy's three main commercial television channels and as Prime Minister also wields influence over RAI, the state broadcaster, has been accused by the Left of using his media power to muzzle critics and satirists.

Three years ago Ms Guzzanti released a widely praised film, Viva Zapatero!, about the suppression in 2003 of her late night show RAIot in which she had satirised the Italian Prime Minister. At the 2005 Venice International Film Festival Viva Zapatero! was given an ovation.

The move to prosecute her over her anti-papal remarks was praised by some on the centre Right, including Luca Volonte, a Christian Democrat, who said that "gratuitous insults must be punished".

However, many people were strongly critical. Paolo Guzzanti, Ms Guzzanti's father and a centre Right MP, said the move was "a return to the Middle Ages”.

"Perhaps my daughter should be submitted to the judgement of God by being made to walk on hot coals," he added.

Antonio Di Pietro, a senator and former anti-corruption magistrate, who organised the rally, said that Ms Guzzanti had only "exercised her constitutional right to freedom of thought.

"You can agree or not agree with what she said — and personally I didn't — but to put people in prison for what they think is reminiscent of a time when those who thought differently had castor oil poured down their throats" — a reference to the Fascist era, when the Laterna Treaty was enacted.

Dario Fo, the Nobel prize-winning playwright, said that applying the treaty more widely would even have led to the prosecution of Dante, since "he put a Pope in the Inferno as well, namely Boniface VIII". Marco Travaglio, a left-wing writer who also addressed the July rally, said: "At this rate Aristophanes and Rabelais would have ended up in prison for being satirists."

Even certain sections of the Church are unimpressed. Father Bartolomeo Sorge, a Jesuit scholar, told La Repubblica the move to prosecute Ms Guzzanzi was incomprehensible. "We Christians put up with many insults, it is part of being a Christian, as is forgiveness. I feel sure the Pope has already forgiven those who insulted him on Piazza Navona."

Condemned to Hell by Dante

Dante’s Inferno condemned Boniface VIII to Hell even before his death. As Dante approaches the circle of those sinners who have committed simony – the buying and selling of church offices – the soul of Pope Nicholas III mistakes Dante for Boniface:

“Shame of the Papal Chair! and art thou come,
Hollow and dismal from the fiery tomb,”
He cried – “a later doom the Prophet told –
But come, Seducer of the Spouse of God,
Who rul’d the christian world with iron rod,
Come! thine eternal revenues behold!”

Translation: Henry Boyd