A parliamentary committee dominated by Silvio Berlusconi's followers yesterday took the first step towards blocking an investigation by prosecutors in which he is formally suspected of paying an underage prostitute and abusing his official position.

The committee, which deals with issues of parliamentary privilege, voted by 11 to eight to recommend that the investigation be declared null and void. Parliament must now vote whether to accept its advice.

The committee had been asked to decide whether the prosecutors could search premises claimed to form part of Berlusconi's political secretariat. But the committee voted on the wider issue of whether the prosecutors should have launched their investigation at all without referring to a special court for offences allegedly committed by ministers in the performance of their duties.

At the centre of the affair is a young Moroccan, Karima el-Mahroug, who is claimed to have visited Berlusconi's villa near Milan while still under the age of 18. The prime minister has acknowledged that, after she was detained on suspicion of theft last May, he telephoned police to say she was the granddaughter of the Egyptian president, Hosni Mubarak.

Berlusconi's lawyers say he believed that she was. The committee endorsed the argument that he was thus acting in an official capacity when he placed the call.

There were further problems for Berlusconi when it was revealed in evidence to Italy's parliament that almost 3kg of cocaine was found last year in the cellar of a flat allegedly provided free to one of his guests at his villa outside Milan.

Marysthell García Polanco, from the Dominican Republic, is a model and former weather announcer known for a celebrated appearance in the "sexy car wash" segment of a popular reality show on one of Berlusconi's channels.

The drugs were part of a haul of more than 12kg allegedly belonging to García Polanco's boyfriend. He was arrested while driving a car belonging to Nicole Minetti, who, prosecutors claim, organised the supply of women for Berlusconi's parties. She and the prime minister have both denied any wrongdoing. Yesterday Berlusconi dismissed the new evidence as "just mud [thrown about] to bad mouth me".

Berlusconi is and then using his position to cover up doing sothe fact. The alleged '"madam'", Nicole Minetti, is caught up in the same investigation, suspected of aiding and abetting prostitution, both juvenile and otherwise.

Wiretap transcripts in the latest documents suggest the strain of the investigation is beginning to tell on Minetti. In one, she is quoted as saying of Berlusconi: "He's behaving like a shit, to save his flaccid arse."

The drugs bust took place before the scandal broke. Garcíía Polanco was not arrested, and there is no suggestion she was aware of the presence of the drugs.

Leaked extracts from the documents in the Italian press indicated that in December she used her friendship with the prime minister to gain access to the prefect of Milan in an apparently unsuccessful attempt to obtain an Italian passport.

According to La Repubblica, a caller, speaking from Berlusconi's private residence in Rome, told her: "We needed to tell you about that appointment with Prefect Lombardi." The caller went on to give the showgirl the number of the direct line to the official's office.

She then reportedly rang the number and told the prefect: "I am calling you in the name of the prime minister." The official, who is in overall charge of law and order in Milan and the surrounding province, fixed an appointment for her, adding that parking would be available for her car.

Corriere della Sera reported that it was the first of two meetings between García Polanco and the prefect and one of seven telephone calls between them. La Repubblica said one ended with the official saying: "Give my regards to the prime minister."