Italy's former PM and self-styled 'most persecuted man' is accused of paying for sex with then 17-year-old exotic dancer

He is no stranger to the courtroom, having spent the past 20 years in a series of battles he says have made him "the most persecuted man by the judiciary in all the history of the entire world".

But the judgment that awaits Silvio Berlusconi – former Italian prime minister, billionaire media tycoon and bunga bunga host – in Milan on Monday is, even by his standards, of some importance.

Two and a half years after he was placed under investigation on suspicion of paying for sex with a 17-year-old girl and then accused of abusing his office to cover it up, the 76-year-old will hear the judges' verdict on a case that raised eyebrows throughout the world and contributed to Berlusconi's scandal-ridden twilight in power.

Prosecutors have called for him to serve six years in jail and be given a lifetime ban on holding public office. But even if he is found guilty, any sentence will be put on hold pending appeal. It could be several years more before a definitive verdict is issued.

Berlusconi is Italy's longest-serving postwar prime minister, and the leader of a centre-right party in the current uneasy coalition government. He denies the charges, saying, with his usual bravado, that he is once again the victim of leftwing magistrates out to get him. While the effects on him may not be felt for a while, there is speculation that a guilty verdict, on top of Berlusconi's other legal woes, could exacerbate tensions in the fractious ruling alliance.

The case in question dates back to Valentine's Day in 2010, when the then prime minister first met Karima el-Mahroug, a 17-year-old nightclub dancer, at his neoclassical villa in Arcore, near Milan.

Nightclub dancer Karima el-Mahroug cries as she appears as a guest on the Italian television show Kalispera. Photograph: Alessandro Garofalo/Reuters

Prosecutors claim Mahroug, widely known by her stage name, Ruby Rubacuori (Heartstealer), visited Berlusconi on a number of occasions between February and May that year, and had sex with him for money.

In Italy, although prostitution is legal, sex workers must be aged 18 or over. Berlusconi denies having "intimate relations" with the then 17-year-old Mahroug, and says he thought that she was in her early 20s. She has said she lied about her age, and denies ever having had sex with him.

Mahroug's testimony – while supporting the former prime minister's claims – has not always made pleasant hearing for Berlusconi. Recently questioned by prosecutors in another, related trial, she said she had lied about many things previously, including having exchanged phone numbers with the football star Cristiano Ronaldo. "If I didn't prostitute myself with someone so handsome, then it is impossible to think I would have done it with Silvio Berlusconi and others," she said.

In sworn testimony at the other trial – in which three of Berlusconi's former associates are accused of procuring prostitutes for him, charges which they deny – Mahroug, now 20, offered lurid details about the soirees which he described as "elegant dinners" with tasteful burlesque entertainment.

Dancers performed striptease acts as nuns, she said, and one even dressed alternately as Barack Obama and Ilda Boccassini, the prosecutor leading the case against Berlusconi. Mahroug said she never saw "contact" between the women and their host.

Villa San Martino in Arcore where Silvio Berlusconi held soirees he described as 'elegant dinners' with tasteful burlesque entertainment. Photograph: Riccardo Schito/Rex Features

In legal terms, the underage prostitution charge is less serious than allegations that Berlusconi abused his office on 27 May 2010 by exerting pressure on Milan police to release her from custody.

The teenager had been arrested that day on suspicion of theft, and within hours the station had received a telephone call from the prime minister, who was in Paris, saying he believed her to be a relative of the then Egyptian president, Hosni Mubarak.

In testimony to court, Berlusconi said he had feared a diplomatic incident, but denied pressurising the police to release her into the care of a hygienist-turned-local politician, Nicole Minetti.

Mahroug has claimed she told people that she was related to Egypt's ousted dictator because she wanted to impress them.

In Italy, defendants are able to appeal twice before a verdict is made definitive. James Walston, politics professor at the American University of Rome, said that a conviction in this case, if it came, would have "almost no effect on Berlusconi because he's prepared everyone so well".

There are concerns, however, that the real effect of a guilty verdict could be on the country's unstable political landscape and Enrico Letta's government, which almost every day sees fresh bickering between Berlusconi's People of Freedom party (PdL) and the centre-left Democratic party (PD).

For the moment, Berlusconi is insisting that he supports the government regardless of his legal problems. But there is anger among the ranks of the PdL, and some party figures would like to see their leader withdraw support from the coalition if his "persecution" by the courts continues – a move that would trigger fresh elections.

Walston said the risk of immediate political instability as a result of the Ruby trial was small. A far bigger concern for Berlusconi and his allies is a tax fraud case in which he has already exhausted one appeal and is approaching a definitive ruling by the court of cassation, Italy's supreme court.

If that conviction is upheld, a four-year jail sentence – and, crucially, a five-year ban on public office – would come into force.

"The point of all this huffing and puffing is to put pressure on the court of cassation [appellate court], to put pressure on the government, to put pressure on [President Giorgio] Napolitano, to do something before the court of cassation hands its verdict down, because that's the important one," said Walston.