Silvio Berlusconi faced new sex allegations today as he braced himself for a crucial test of his government in parliament.

A woman who worked as a prostitute told prosecutors in a corruption inquiry that the prime minister gave her presents on a night when she and two other women shared his bed, according to a report in the Italian daily La Repubblica.

"I, the two girls from Rome and Berlusconi were in the bed," Maria Teresa de Nicolò was quoted as saying, without identifying the two others.

De Nicolò, 38, was one of numerous women to have said they were paid by a businessman from Bari to attend dinners at Berlusconi's private residence in Rome in 2008-9. She is the second who said she spent the night there, reports claimed.

The businessman, Gianpaolo Tarantini, is one of several suspects in an investigation into alleged corruption in the health service in the south-eastern region of Puglia. Tarantini, who denies wrongdoing, has not been indicted. According to earlier leaks, Tarantini told prosecutors he was trying to ingratiate himself with Berlusconi to enhance his business prospects. The prime minister gave him an introduction to a junior minister with a large budget at his disposal, but Tarantini did not receive any government contracts as a result.

The publication of De Nicolò's statement will come as an embarrassment to Berlusconi, who is due to meet David Cameron in Rome tomorrow. Two hours before that, Berlusconi will face a key vote in the chamber of deputies, where he lost his majority last week after a revolt led by his longstanding ally Gianfranco Fini.

However, Berlusconi's chances of avoiding a humiliating defeat rose today when it was announced that Fini's supporters had agreed with three other parties to abstain from the ballot. The vote is on an opposition demand for a junior justice minister, under investigation in a criminal conspiracy inquiry, to be sacked.

The deal represented a U-turn by Fini, who had earlier said members of the government who became suspects should resign. It appeared to presage the emergence of a new alliance in the centre of Italian politics made up of Fini's rebels, Christian Democrats and Sicilian regionalists.

Questions have been raised about the prime minister's conduct at a time when his government was preparing legislation to penalise streetwalkers and their clients, although not agency sex workers. Berlusconi has said he was unaware the women were paid.

De Nicolò told her interrogators about "the hours I slept alone and the hours when, instead, some hours, I was with these girls, these two from Rome, and Berlusconi."

She said there were "perhaps 15" women at the dinner. The following morning she received €1,000 [£800] from Tarantini.

She claimed the prime minister gave her jewellery, but also said that all the invited women received such gifts.