Berlusconi's party accused of buying out opponents

Mr Berlusconi, 74, needs his People of Freedom party to win or he faces going to the polls before a scheduled 2013 general election, and the result is said to be balanced on a knife edge.

The inquiry was opened after former magistrate Antonio Di Pietro, who is now head of the anti-corruption party Italy of Values, lodged an official complaint with prosecutors after the allegations appeared in the Italian media.

Some polls have given Berlusconi's party a narrow lead - which follows accusations that at least three opposition MPs, including two from Italy of Values, have been "bought".

It has been reported in Italian media that MPs have been offered help with paying "their mortgages, as well as government positions" in order to secure the vital victory for billionaire Mr Berlusconi.

Last night, Mr Di Pietro said: "I want prosecutors to investigate this buying and selling of votes. Not only is it like a cattle market, it is humiliating.

"The judiciary should establish whether in a normal country it is possible for people elected for one party to be persuaded to vote for another and on what basis they have changed their mind."

Mr Di Pietro was speaking after it emerged that two MPs from his party - Antonio Razzi and Domenico Scilipoti - were backing Mr Berlusconi in Tuesday's confidence vote.

He immediately reported his concerns to Rome prosecutors Alberto Caperna and Giovanni Ferrara, with sources at their office saying an "allegation of corruption by persons unknown" was being investigated and that "evidence was being sought".

Pier Luigi Bersani, leader of the opposition Democratic Left said: "A crime is being committed in parliament. There is a scandal and we should be embarrassed in front of all the other democracies in the world."

James Walston, a lecturer in Italian politics at the American University of Rome, said: "This buying-up of votes is openly taking place and it is quite sleazy but that is nothing new in Italian politics.

"These MPs are on the shopping list of the People of Freedom and have been offered money, positions, consultancies, and as a result it's very possible that Berlusconi may just clinch a win.

"Mr Di Pietro is incorruptible but a lot of his people although talking the talk, do not walk the walk and they simply do not follow him - that's why even if Berlusconi wins I'm sure we will be back in a similar situation next month."

A series of scandals involving a teenage dancer attending a party he hosted and an escort paid to have sex with him have pushed Mr Berlusconi towards the confidence vote.

He has also lost his ally of 14 years Gianfranco Fini, who fell out with him over an immunity law which would see senior political figures exempt from being prosecuted while in office.

However, Mr Berlusconi is confident of victory and said: "We will obtain the majority and we will continue to govern. We have not bought anyone's vote, these are ridiculous accusations."