Antonio di Pietro delivered the signatures himself

Antonio Di Pietro gathered the signatures in order to force a referendum on the immunity law - which was passed in June as a court tried Mr Berlusconi on charges of bribing judges.

If the court accepts that 500,000 of the signatures are valid, the referendum will go ahead.

We want to give back dignity to our country, which is laughed at, disdained, scorned, humiliated, offended worldwide Antonio Di Pietro

Mr Di Pietro made his name a decade ago as the public prosecutor who carried out a crusade against political corruption in Italy.

He caused a minor political revolution when the two political parties which had governed Italy almost uninterruptedly since the fall of fascism - the Christian Democrats and the Socialists - were forced to dissolve themselves.

Cardboard boxes

Mr Di Pietro delivered dozens of cardboard boxes crammed with signatures to the court, delivering the cargo himself.

WHERE THE CENTRE-LEFT STANDS For the referendum Greens Communists Italy of Values (Di Pietro's own party) Strong reservations Democrats of the left Social Democrats Daisy (centrist)

He told Italian radio: "We want to give back dignity to our country, which is laughed at, disdained, scorned, humiliated, offended worldwide, not because there was a prime minister on trial, but because there was and is a prime minister who has made a law for himself to avoid being on trial."

The former judge complained that because of Mr Berlusconi's near monopoly of the media in Italy only foreign news organisations had reported his campaign.

However, not all opposition parties are supporting Mr Di Pietro's initiative.

Some say that if the quorum of 50% of eligible voters is not reached, the referendum could actually boost the prime minister.

Over the summer Mr Di Pietro made a whistlestop tour of Italy armed only with a megaphone and some paper for collecting signatures.

He said he had around 5,000 supporters who gave up their holidays to work for his party.