As the Italian prime minister's political allies start to edge away from him, revelations from another starlet have pitched him further into crisis

She is 23, beautiful and ambitious. And if her story turns out to be true, Barbara Montereale may yet prove to be the young starlet who brings about the downfall of the Italian prime minister, Silvio Berlusconi.

Montereale is the latest in a succession of young women who have come forward to testify to the private entertainments enjoyed by Berlusconi at his residence in Rome and his holiday villa in Sardinia.

For just over a month, ever since the prime minister's wife, Veronica Lario, publicly accused him of "frequenting minors", the Italian media have revelled in tales of squads of handpicked showgirls, models and actresses flown in for summer parties and risqué evenings at the Villa Grazioli in Rome.

The stories, complete with paparazzi photographs of topless women and a naked former Czech prime minister, have suggested a world whose inhabitants were living on the edge of moral propriety. But yesterday's interview with Montereale in La Repubblica, in the wake of his much-questioned friendship with an 18-year-old model, Noemi Letizia, may convince many ordinary Italians that a line has been crossed.

According to Montereale, last November she travelled with Patrizia D'Addario, a former model and escort, to a dinner in Rome hosted by Berlusconi, and then to Berlusconi's Sardinian retreat, Villa Certosa, in January. For making the Sardinia trip, she was paid €1,000 by hospital equipment vendor Giampaolo Tarantini, who is now under investigation by Bari investigators for abetting prostitution.

Montereale claims Berlusconi gave her "rings and necklaces that he said he designed" and a CD of Neapolitan love songs in Rome. After her stay in Sardinia, she left with a bag containing "a very generous sum of money". She denied having sex with Berlusconi, but was happy to give a graphic account of how the November night with D'Addario in Rome had unfolded.

"Everyone knew at the dinner she was an escort," Montereale told La Repubblica. At the end of the dinner, she said "the agreement was that Giampaolo [Tarantini] and I would leave Patrizia alone with the PM, and that's what we did." D'Addario, according to Montereale, returned to the hotel that had been booked for the women at 8am the next day.

"She told me she had had sexual relations with the prime minister," said Montereale. "She added that she had not been paid. She said she wasn't interested in money because she wanted him to help her in relation to a hotel she wanted to build." Again according to Montereale, that prime ministerial assistance never materialised, leading an embittered D'Addario to tell her story last week and reveal that she had handed audio and video tapes to the police.

Asked to comment on the story, a spokesman for Berlusconi, Marco Ventura, said yesterday: "We have no comment; we have nothing to say." But the aftershock of the visit by Montereale and D'Addario to the Villa Grazioli has contributed to the sense of crisis that is now in danger of overwhelming Berlusconi's premiership. In April, few would have imagined that the extraordinary attendance of Berlusconi at the 18th birthday party of Letizia would have led to such a devastating series of revelations.

Last week even the Roman Catholic Church, for which Berlusconi has been a useful ally, felt the need to distance itself from the prime minister. Avvenire, the official newspaper of the Italian conference of bishops, said his own supporters now wanted him to come clean on his escapades.

"This is becoming more and more damaging, particularly since the Church has now waded in," said James Walston, professor of international relations at the American University in Rome. "It is not necessarily the scandal itself, which most people do not care about, but the fact it seems he is no longer in control. The government will not, however, collapse in the near future, but he is certainly weaker."

By last Thursday, Berlusconi felt compelled to rebuff rumours that a transition government, run by the governor of the Bank of Italy, could be set up if he resigned.

The next night, when he was booed and heckled at a political rally in Milan, the enraged prime minister berated his critics, shouting: "You disgust and repel me. But you communists without dignity will never bring me down."

Meanwhile Antonio Di Pietro, the former magistrate who has become a respected opposition politician, has compared Berlusconi with the Roman emperor Nero. Even on the right, among Berlusconi's political allies, there is growing concern and the beginnings of a revolt. Gianfranco Fini, the speaker of the lower house of parliament and a key Berlusconi ally, has publicly warned that the number of starlets with stories to tell is threatening to turn voters away from politics. The influential journalist and loyal supporter Giuliano Ferrara said that the prime minister "needs to choose his friends better".

Some of the arguments used in Berlusconi's defence border on the surreal. Vittorio Feltri, the editor of the right-wing newspaper Libero, claimed that, ever since Berlusconi's operation for prostate cancer in 1996, he could no longer have sex. "To say he is a sex maniac is simply ridiculous," he wrote.

Nicolò Ghedini, Berlusconi's chief legal adviser, defended his client over the D'Addario affair by describing his client as a mere "end user" of the women, who was not therefore at risk in the Bari investigation. For good measure, he added that "Berlusconi could have them [women] in large numbers for free".

The prime minister himself, although clearly rattled, is still trying to banter his way though the storm, using the brazen style that has gone down well in the past with many voters. On Friday, he spotted a female journalist whose sweater had slipped slightly off one shoulder. "Are you trying to get invited to one of my dinners?" he asked. "I used to do one a month, now I need to organise three or four a week."

But after the latest starlet breaks cover, how many Italian are still laughing?

Berlusconi's women

Veronica Lario

Soon to be ex-wife of Silvio. Has spoken little since accusing him of "frequenting minors", but may cause trouble if divorce deal is not to her liking.

Noemi Letizia

Aspiring model whose 18th birthday party Berlusconi attended. Damage limited after the Letizias said he was an old family friend.

Patrizia D'Addario

Model, singer and alleged escort girl who told of evenings in Rome with Berlusconi. Reportedly taped visits on film.

Sabina Began

Actor known as the "queen bee" for organising parties for Berlusconi. A devotee of the PM, has now gone to ground.

Barbara Montereale

Friend of D'Addario who has just revealed that bags of money were handed out to girls at Villa Certosa.