Magistrate Ilda Boccassini vows to cut pre-trial hearings and have the Italian PM in court this summer in a prostitution case

For a man who likes to say he loves women, Silvio Berlusconi may make an exception for Ilda Boccassini, the crusading Milan magistrate who could yet convict him this year for sex offences.

Known as Ilda La Rossa (Ilda the Red), thanks to her flame-coloured hair and progressive sympathies, the Neapolitan-born veteran of mafia cases is one of a trio of Milan magistrates now investigating the Italian prime minister on suspicion that he paid to have sex with an underage prostitute. Berlusconi is also accused of abusing his position to pressure police.

La Rossa's determination to pursue the case has led her to request that, if the case comes to court, pre-trial hearings which slow Italian prosecutions to a crawl will be skipped, meaning that Berlusconi may find himself in the dock as early as this summer.

The development is a serious blow to Berlusconi, who had appeared to emerge relatively unscathed after allegations in 2009 of sleeping with another prostitute, Patrizia D'Addario. Although he was subsequently abandoned by his wife and caught up in other scandals involving young women, a no-confidence vote in the Italian parliament was defeated at the end of last year. But his government hangs by a thread and can ill afford another sex drama.

The investigation will examine allegations that Berlusconi paid to sleep with a nightclub dancer, Karima El Mahroug, known as Ruby the Heartstealer, when she was 17, and subsequently had her freed from a Milan police station – where she was being held on suspicion of theft – by fooling officers into thinking she was the granddaughter of the Egyptian president, Hosni Mubarak. If found guilty, the 74-year-old prime minister faces up to 15 years in jail.

Last week an Italian court ruling partly overturned a law shielding the prime minister from any trials he may face while in office.

Berlusconi claimed on Friday that Boccassini and her colleagues were "subverting the fundamental rules of democracy" and joked that they were just "jealous" not to have been invited to the parties at his mansion outside Milan where he entertained Mahroug and scores of other young women.

For Boccassini, who is demanding Berlusconi submit to interrogation this month, the inquiry marks her latest probe into the private life and business dealings of the media mogul since the 1990s. She once said that tackling Berlusconi was tougher than taking on the mafia, against which she has racked up numerous successes.

Described by wiretapped mafiosi as a "tiger" who will stop at nothing, this year, she crippled operations in northern Italy run by the Calabrian Ndrangheta mafia by mounting raids which netted 300 suspects.

The 61-year-old is the daughter of a magistrate and a mother of two who fiercely defends her private life. Boccassini's refusal to gossip with the press about investigations may also explain how the latest Berlusconi probe has been under wraps since its launch in December.

Details now released show investigators believe Berlusconi's "Bunga Bunga" party guest list extended beyond Mahroug to a regular cast of beautiful women he put up in apartments in Milan. Police raided the apartments last week seeking evidence of cash payments to the women to back up suspicions they were paid to have sex with Berlusconi. Mahroug admits to receiving €7,000 from Berlusconi, although she denies having sex with him.

Tracing her movements through mobile phone records, investigators believe she attended six parties and was at Berlusconi's villa last April during a visit by Vladimir Putin.

Corriere della Sera reported that residents included Iris Berardi, a former Miss Italy contestant, the twins Eleonora and Imma De Vivo, who have appeared in an Italian reality TV show, and Ioana Visan, an escort previously recruited to attend Berlusconi's Rome parties by Giampaolo Tarantini, the businessman who hired Patrizia D'Addario.

Investigators believe that the stable of women was run by Nicole Minetti, a half-British dental hygienist and TV showgirl who rose to become a politician in Milan after working on Berlusconi's teeth.

Friends of Minetti, one of whom attended a party thrown by Berlusconi last September, confirmed to investigators the existence of a "Bunga Bunga" room at his mansion, with poles set up for pole dancing. Topless women in nurse and police costumes performed stripteases for Berlusconi, aiming to outperform fellow guests and be asked to stay behind for the night in return for payments of up to €10,000, it was reported in La Repubblica.