Prosecutors sum up, saying there was 'no doubt' that then PM paid for sex with underage prostitute and abused his office to cover it up

Prosecutors are demanding that Silvio Berlusconi, Italy's former Italian prime minister and key backer of the fragile new government, serve six years in prison and be banned from public office for life for allegedly paying for sex with an underage prostitute and abusing his office to cover it up.

Presenting her long-awaited closing arguments in the so-called Rubygate trial, Ilda Boccassini, the prosecutor who has led the case against Berlusconi, said the centre-right billionaire should be convicted on both charges involving Karima el-Mahroug, a former nightclub dancer from Morocco whose stage name was Ruby Heartstealer.

A verdict is expected in the coming months. If he is found guilty, Berlusconi will be able to launch two appeals, a process that would take years to complete.

Boccassini argued that there was "no doubt" that the then prime minister had paid for sex with Mahroug when she was 17 – under the legal age for prostitution in Italy. She also argued that when, in May 2010, the teenager was arrested on suspicion of theft, Berlusconi had put pressure on the police to release her, claiming she was a relative of the now-deposed Egyptian president Hosni Mubarak.

Berlusconi, a three-time premier whose Freedom People (PdL) party shares power in Enrico Letta's grand coalition government and is leading once again in the polls, strongly denies both charges, claiming the trial is just another episode in his "persecution" by Italy's magistrates.

On Saturday, he turned a political rally in the northern city of Brescia into a protest against the Italian judiciary, which was attended by Angelino Alfano, the new interior minister – much to Letta's irritation.

And, in a bizarre intervention on the eve of the summing-up, Berlusconi appeared on one of his own television channels on Sunday to insist that he had never been anything but a benevolent friend to Mahroug and had given her some money purely out of a desire to help her build a life for herself.

The young woman also appeared on the show, which gave viewers a glimpse inside the Arcore villa near Milan where so-called "bunga bunga" soirees took place, including a dimly lit basement area and dining room with crimson tablecloth and candelabra.

Mahroug, now 21, denies sleeping with the media tycoon and says she lied to him about her age and about her "fantasy" connection to Mubarak. She insisted on Canale 5 on Sunday night that, though it might have been the easy optionfor her, prostitution was "against [her] principles".

Boccassini, however, painted a very different picture of Mahroug, arguing in court that she had bought into a negative "Italian dream" of getting into show business to make money. Raising eyebrows, the prosecutor referred to Mahroug as "an intelligent person … with that oriental cunning of her origins".

She added: "Let there be no doubt that Karima Mahroug had sex with Berlusconi and received benefits for it." It had been proved beyond reasonable doubt, she argued, that the "girls invited [to Arcore] were part of a prostitution system organised to satisfy the sexual pleasure of Silvio Berlusconi".

Boccassini requested a prison term of five years for the abuse of office charge and one year for the underage prostitution charge.

Monday's summing up had been delayed for weeks – first because of an eye condition suffered by Berlusconi and then over a request by his lawyers, which was rejected, to have the trial moved from Milan to nearby Brescia.

In the meantime, the former prime minister's conviction for tax fraud – which carries a four-year jail sentence and a five-year ban from public office – was upheld. He denies the charges. The penalties will not come into effect unless the verdict is made definitive after a second appeal, by which time the statue of limitations may well have expired. In a comment on the prosecutor's request Berlusconi said on Monday night: "Theories, innuendo, twisting, falsehoods inspired by prejudice and hate, all against the evidence, beyond the imaginable and the ridiculous. But everything is allowed beneath the shield of [judicial] robes. Poor Italy!".