Prodi, a 68-year-old academic known in Italy as the "professor", decided to go ahead with the vote, rejecting the advice of Giorgio Napolitano, Italy's president, to step down.

In a statement, Prodi said: "I have told the president I will go to the senate."

Roberto Calderoli, a senator from the far-right Northern League and one of Prodi's most acerbic critics, said he admired Prodi's courage.

Berlusconi's centre-right opposition, which was beaten by Prodi in the 2006 elections, hopes Napolitano will then call early elections which it is confident of winning.

However, there is a groundswell of pressure in Italy for much needed reforms to current election rules.

The system was tampered with by Berlusconi before the last elections and is widely blamed for the unstable system of fragmented coaltions whose bickering have dogged Prodi's tenure.

Commentators and analysts warn that holding early elections without changing the messy voting rules would merely prolong the instability which has affected Italy's economy.

Technical government

To win, Prodi needs the support of a handful of unelected life senators who have rescued him in previous votes and some elected senators would have to throw him a lifeline by not showing up for the vote, lowering the quorum.

If he loses, Napolitano could ask Prodi or another senior politician or technocrat to form an interim government with a mandate for electoral reform before new elections are called.

Italy has turned to technical governments before in times of crisis and some economists see it as a positive option.